Food Packaging
Principles and Practice
Gordon L. Robertson
0
CRC
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xxiii
Preface to the Third Edition
Although it is only seven years since the second edition was completed, there have been significant developments in food packaging that warrant a third edition. This edition has been substantially rewritten, updated and extended to include the many developments in food packaging that have taken place since the second edition was published.
Having used the second edition as the course notes for workshops attended by nearly 600 people around the world, I have gained a good appreciation of which areas work well and which are in need of greater clarification and/or amplification. All the worked examples have been changed and new examples added where appropriate. As well, all the references have been updated and now number more than 1000, of which almost two-thirds have been published since 2005. There is also a 64% increase in the number of figures.
Biobased packaging has moved to center stage since the second edition was written. Therefore, Chapter 3 has been expanded to reflect this, becoming the longest chapter in the book; it includes a new section on bionanocomposites. The chapters on optical and mechanical properties of plastics, which appeared in the first edition, have, by popular request, been combined with permeability properties to form a new Chapter 4. In Chapter 5, the section on metallization has been expanded to include details of new coating methods to improve the barrier properties of plastic and paper packaging, including atomic layer deposition, which has recently been commercialized. As well, a major new section on the application of nanoclays to improve the barrier properties of plastic packaging has been added. The section in Chapter 5 on heat sealing, together with the section on closures for glass from Chapter 8, has been moved to a new Chapter 10 which also includes fresh sections on closures for plastic and com-posite containers in addition to recent research on openability and consumer strength and dexterity.
Other changes include a new section on the packaging of vegetable oils (in particular olive oil) and an update on legislative and safety aspects of food packaging in an attempt to do justice to the increasing regulatory and public interest in food contact materials such as BPA and phthalates and the associated issues of estrogenicity and risk assessment. The section on migration from the first edition has been added in abbreviated form to this chapter. The final chapter has been expanded in two key areas to reflect the huge increase in interest and published research in this area since the second edition was written: life cycle assessment (including carbon footprinting) and sustainability.
It would not have been possible to complete this book without assistance, encouragement and helpful advice from a number of people. I would especially like to thank the following: David Clark, Ian Darby, Bruce Gunn, Gary Hodgson, Dr. Robert V. Holland, Professor John M. Krochta, Professor Dong Sun Lee, Dr. Roger D. MacBean, Dr. Pornchai Rachtanapun, Per O. Risman, Elina Rusko, Dr. Kevin C. Spencer, Professor Tetsuya Suzuki, Dr. Noemi Zaritzky and Dr. David A. Zumbrunnen.
Once again, it is a real pleasure to acknowledge the tremendous assistance of my wife, Soozie, who has improved the look of the book by preparing all the artwork and assisting in numerous other ways: thank you so much.
In the expectation that this edition will be as popular as its predecessors, the possibility of a fourth edition is very real. Therefore, expressions of interest are invited from suitably qualified individuals who would like to be considered as coauthors for a fourth edition.
Finally, I would like to thank all those who provided feedback, constructive comments and suggestions for improvements on the second edition. I welcome further comments on this edition (including any errors which may have crept in), which I will be happy to consider in a fourth edition.
Gordon L. Robertson
[email protected] www.gordonlrobertson.com
v
Contents
Preface to the Third Edition ... xxiii
Preface to the Second Edition ...xxv
Preface to the First Edition ...xxvii
Author ...xxix
Chapter 1 Introduction to Food Packaging ...1
1.1 Introduction ... 1 1.2 Definitions ... 1 1.3 Functions of Packaging ... 2 1.3.1 Containment ... 2 1.3.2 Protection ... 3 1.3.3 Convenience ... 3 1.3.4 Communication ... 4 1.4 Package Environments ... 4 1.4.1 Physical Environment ... 4 1.4.2 Ambient Environment ... 5 1.4.3 Human Environment ... 5 1.5 Functions/Environment Grid ... 5 1.6 Packaging Innovation ... 6 1.7 Finding Information ... 8 References ... 8
Chapter 2 Structure and Related Properties of Plastic Polymers ... 11
2.1 Introduction ... 11
2.2 History ... 11
2.3 Factors Influencing Polymer Structures and Related Properties ... 12
2.3.1 Molecular Structure... 13 2.3.1.1 Classification of Polymers ... 13 2.3.1.2 Polymerization Processes ... 14 2.3.2 Molecular Weight ... 15 2.3.3 Density... 16 2.3.4 Crystallinity... 16
2.3.5 Physical Transitions in Polymers ... 17
2.3.6 Chemical Structure ...20 2.3.6.1 Polyolefins ...20 2.3.6.2 Copolymers of Ethylene ... 28 2.3.6.3 Substituted Olefins ... 31 2.3.6.4 Polyesters ... 35 2.3.6.5 Polycarbonates ... 39 2.3.6.6 Polyamides ... 39 2.3.6.7 Acrylonitriles ... 43
2.3.7 Additives in Plastics ...44
2.3.7.1 Processing Additives...44
2.3.7.2 Plasticizers ...44
2.3.7.3 Antiaging Additives ...44
2.3.7.4 Surface Property Modifiers ... 45
2.3.7.5 Optical Property Modifiers ... 45
2.3.7.6 Foaming Agents ... 45
References ...46
Chapter 3 Edible, Biobased and Biodegradable Food Packaging Materials ... 49
3.1 Introduction ... 49
3.2 Edible Packaging Materials ... 50
3.2.1 Polysaccharides ... 51 3.2.1.1 Starch ... 51 3.2.1.2 Cellulose ... 52 3.2.1.3 Hemicellulose ... 52 3.2.1.4 Chitosan ... 52 3.2.1.5 Gums ... 53 3.2.2 Lipids ... 53 3.2.3 Proteins ... 54 3.2.4 Composite Materials ... 55 3.2.5 Film Additives ... 55 3.2.5.1 Plasticizers ... 55 3.2.5.2 Emulsifiers ... 55 3.2.5.3 Antimicrobials ... 56 3.2.5.4 Antioxidants ... 57 3.2.6 Bionanocomposites ... 57 3.2.7 Commercialization ... 57
3.3 Biobased and Biodegradable Packaging Materials ... 58
3.3.1 Classification ... 58
3.3.2 Degradability Definitions ... 59
3.3.3 Assessing Biodegradability of Biobased Polymers ... 61
3.3.4 Oxo-Biodegradable (OBD) Polymers ... 63
3.3.5 Category 1 ...64 3.3.5.1 Starch ...64 3.3.5.2 Cellulose ... 65 3.3.5.3 Hemicellulose ... 67 3.3.5.4 Chitosan ... 67 3.3.5.5 Others... 67 3.3.6 Category 2 ... 68 3.3.6.1 Poly(lactic acid) ... 68 3.3.6.2 Biopolyethylene ... 69 3.3.6.3 Biopoly(ethylene terephthalate) ... 69 3.3.7 Category 3 ... 70 3.3.7.1 Poly(hydroxyalkanoates) ... 70 3.3.7.2 Bacterial Cellulose ... 71 3.3.8 Category 4 ... 72 3.3.8.1 Poly(caprolactone) ... 72 3.3.8.2 Poly(glycolic acid) ... 73
3.3.8.3 Poly(butylene adipate-co-terephthalate) ... 73
3.3.8.4 Poly(butylene succinate) and Copolymers ... 73
3.3.8.5 Poly(propylene carbonate) ... 74
3.3.9 Properties of Biobased Packaging Materials ... 74
3.3.9.1 Barrier Properties ... 74
3.3.9.2 Mechanical Properties ... 76
3.3.10 Current Limitations ... 79
3.3.11 Methods to Improve Functionality ... 79
3.3.12 Bionanocomposites ... 79
3.3.13 Food Packaging Applications ... 81
3.4 Environmental Aspects ... 82
3.5 Future Trends ... 85
References ... 86
Chapter 4 Optical, Mechanical and Barrier Properties of Thermoplastic Polymers ... 91
4.1 Introduction ... 91 4.2 Optical Properties ... 91 4.3 Tensile Properties ... 92 4.4 Bursting Strength ... 94 4.5 Impact Strength ... 94 4.6 Tear Strength ... 95 4.7 Stiffness ... 96
4.8 Crease or Flex Resistance ... 96
4.9 Coefficients of Friction ... 97
4.10 Blocking... 97
4.11 Orientation and Shrinkage ... 97
4.12 Barrier Properties ... 98
4.12.1 Introduction ... 98
4.12.2 Theory ... 98
4.12.3 Steady-State Diffusion ... 101
4.12.4 Unsteady-State Permeation ... 102
4.12.5 Permeation through Pores ... 103
4.12.6 Permeability Coefficient Units ... 104
4.12.7 Polymer/Permeant Relationships ... 109
4.12.8 Variables of the Polymer ... 111
4.12.9 Factors Affecting the Diffusion and Solubility Coefficients ... 113
4.12.9.1 Pressure ... 113
4.12.9.2 Sorption... 114
4.12.9.3 Temperature ... 115
4.12.10 Transmission Rate ... 117
4.12.11 Migration ... 122
4.12.12 Permeability of Multilayer Materials ... 122
4.12.13 Measurement of Permeability ... 125
4.12.13.1 Gas Permeability ... 125
4.12.13.2 Water Vapor Permeability ... 127
4.12.13.3 Permeability of Organic Compounds ... 128
Chapter 5 Processing and Converting of Thermoplastic Polymers ... 131
5.1 Extrusion ... 131
5.1.1 Monolayer Extrusion ... 131
5.1.2 Coextrusion ... 133
5.2 Calendering ... 134
5.3 Coating and Laminating ... 134
5.3.1 Surface Treatment ... 135 5.3.1.1 Surface Energy ... 135 5.3.1.2 Corona Treatment ... 135 5.3.1.3 Flame Treatment ... 136 5.3.1.4 Priming ... 136 5.3.1.5 Chemical Treatment... 136 5.3.2 Coating Processes... 136 5.3.3 Laminating Processes ... 137 5.4 Blending ... 138 5.5 Vapor Deposition ... 139
5.5.1 Physical Vapor Deposition ... 140
5.5.2 Chemical Vapor Deposition ... 142
5.5.2.1 Plasma-Enhanced Chemical Vapor Deposition ... 142
5.5.2.2 Combustion Chemical Vapor Deposition ... 146
5.5.3 Atomic Layer Chemical Vapor Deposition ... 146
5.6 Nanocomposites... 147
5.6.1 Nanoclays ... 147
5.6.2 Intercalation and Exfoliation ... 148
5.6.3 Synthesis of PCNs ... 149 5.6.4 Barrier Properties ... 150 5.6.5 Applications ... 150 5.6.6 Bionanocomposites ... 151 5.6.7 Future Developments ... 151 5.7 Orientation ... 152 5.7.1 Orientation Processes ... 153 5.7.2 Shrink Films ... 155 5.7.3 Stretch Films ... 155 5.8 Cross-Linking ... 156 5.9 Microperforation ... 157 5.10 Injection Molding ... 158 5.11 Blow Molding ... 159
5.11.1 Extrusion Blow Molding ... 159
5.11.2 Injection Blow Molding ... 160
5.11.3 Stretch Blow Molding ... 161
5.12 Thermoforming ... 163
5.13 Foamed (Cellular) Plastics ... 163
References ... 164
Chapter 6 Paper and Paper-Based Packaging Materials ... 167
6.1 Pulp ... 167
6.1.1 Introduction to Pulping ... 168
6.1.2 Mechanical Pulps ... 169
6.1.3.1 Alkaline Processes ... 170 6.1.3.2 Sulfite Processes ... 170 6.1.4 Semichemical Pulps ... 171 6.1.5 Digestion... 171 6.1.6 Bleaching ... 172 6.1.6.1 Mechanical Pulps ... 172 6.1.6.2 Chemical Pulps ... 172 6.1.6.3 Recycled Pulps ... 173 6.2 Paper ... 173
6.2.1 Beating and Refining ... 174
6.2.2 Papermaking ... 175
6.2.2.1 Fourdrinier Machine ... 175
6.2.2.2 Cylinder Machine ... 176
6.2.2.3 Twin-Wire Formers ... 176
6.2.2.4 Presses and Dryers ... 177
6.2.3 Converting ... 177 6.2.3.1 Calendering ... 177 6.2.3.2 Sizing ... 178 6.2.3.3 Barrier Coatings... 178 6.2.3.4 Pigments ... 180 6.2.4 Physical Properties ... 180 6.2.5 Types of Paper ... 181 6.2.5.1 Kraft Paper ... 181 6.2.5.2 Bleached Paper ... 181 6.2.5.3 Greaseproof Paper ... 181 6.2.5.4 Glassine Paper ... 181 6.2.5.5 Vegetable Parchment ... 182 6.2.5.6 Waxed Paper ... 182 6.3 Paperboard Products ... 182 6.3.1 Folding Cartons ... 183 6.3.2 Beverage Cartons ... 184
6.3.3 Molded Pulp Containers ... 185
References ... 186
Chapter 7 Metal Packaging Materials... 189
7.1 Introduction ... 189
7.2 Manufacture of Tinplate ... 190
7.2.1 Manufacture of Pig Iron ... 190
7.2.2 Steelmaking ... 191 7.2.3 Tinplating ... 193 7.3 Manufacture of ECCS ... 195 7.4 Manufacture of Aluminum ... 195 7.5 Container-Making Processes ... 197 7.5.1 End Manufacture ... 197
7.5.2 Three-Piece Can Manufacture ... 198
7.5.2.1 Welded Side Seams ... 198
7.5.2.2 Soldered Side Seams ... 199
7.5.3 Two-Piece Can Manufacture ...200
7.5.3.1 Drawn and Ironed ... 201
7.5.3.2 Drawn and Redrawn ...202
7.5.4 Protective and Decorative Coatings ... 203
7.5.4.1 Protective Coatings ... 203
7.5.4.2 Decorative Coatings ...209
7.6 Aluminum Foils and Containers ...209
7.6.1 Aluminum Foil ...209
7.6.2 Tube ... 210
7.6.3 Retort Pouch ... 210
7.6.4 Bottle ... 212
7.7 Corrosion of Metal Packaging Materials ... 212
7.7.1 Fundamental Concepts ... 212
7.7.1.1 Introduction ... 212
7.7.1.2 Electrochemical Corrosion ... 212
7.7.1.3 Electrochemical Series ... 213
7.7.1.4 Factors Affecting the Rate of Corrosion... 215
7.7.1.5 Passivity ... 215
7.7.1.6 Stress Corrosion Cracking ... 216
7.7.2 Corrosion of Tinplate ... 216
7.7.2.1 Corrosion of Plain Tinplate Cans ... 216
7.7.2.2 Corrosion of Enameled Cans ... 218
7.7.2.3 Corrosiveness of Foods ... 220
7.7.2.4 Effects of Processing and Storage ... 223
7.7.2.5 External Corrosion of Cans ...224
7.7.3 Corrosion of ECCS ... 226
7.7.4 Corrosion of Aluminum ... 226
References ... 227
Chapter 8 Glass Packaging Materials ... 229
8.1 Introduction ... 229
8.2 Composition and Structure ... 229
8.3 Physical Properties ... 231
8.3.1 Mechanical Properties ... 231
8.3.2 Thermal Properties ... 232
8.3.3 Optical Properties... 233
8.4 Manufacture... 234
8.4.1 Mixing and Melting... 234
8.4.2 Forming Processes ... 235
8.4.2.1 Blow and Blow ... 235
8.4.2.2 Wide Mouth Press and Blow ... 236
8.4.2.3 Narrow Neck Press and Blow ... 237
8.4.3 Annealing ... 237
8.4.4 Surface Treatments ... 237
8.4.4.1 Hot-End Treatment ... 237
8.4.4.2 Cold-End Treatment ... 238
8.4.4.3 Shrink Sleeves ... 238
8.5 Glass Container Design ... 238
8.5.1 Glass Container Nomenclature... 239
8.5.2 Glass Container Strength Factors ...240
8.6 Closures for Glass Containers ... 241
References ... 241
Chapter 9 Printing Processes, Inks, Adhesives and Labeling of Packaging Materials ... 243
9.1 Introduction ... 243 9.2 Printing Processes ...244 9.2.1 Relief ...244 9.2.1.1 Letterpress ...244 9.2.1.2 Flexography ...244 9.2.1.3 Flexo Process ... 245 9.2.2 Gravure ...246 9.2.3 Lithography ... 247 9.2.4 Screen ...248 9.2.5 Digital ...248 9.2.5.1 Ink-Jet ... 249 9.2.5.2 Electrophotography ... 249 9.3 Inks ... 250 9.3.1 Introduction ... 250
9.3.1.1 Below the Surface ... 251
9.3.1.2 On the Surface ... 251
9.3.1.3 Above the Surface ... 251
9.3.1.4 Through the Surface ... 251
9.3.1.5 No Surface ... 251 9.3.2 Ink Components ... 251 9.3.3 Liquid Inks ... 253 9.3.3.1 Flexographic Ink ... 253 9.3.3.2 Gravure Ink ... 253 9.3.3.3 Screen Ink ... 254 9.3.3.4 Digital Ink ... 254 9.3.4 Paste Inks ... 255
9.3.4.1 Offset Lithographic Inks ... 255
9.3.4.2 Letterset Inks ... 255 9.3.4.3 Letterpress Inks ... 255 9.3.5 Thermochromic Inks ... 255 9.4 Adhesives ... 256 9.4.1 Natural Materials ... 257 9.4.1.1 Starch ... 258 9.4.1.2 Protein ... 258
9.4.1.3 Natural Rubber Latex ... 258
9.4.2 Synthetic Materials... 259 9.4.2.1 Water-Borne Adhesives ... 259 9.4.2.2 Hot-Melt Adhesives ... 259 9.4.2.3 Solvent-Based Adhesives ... 259 9.4.2.4 Pressure-Sensitive Adhesives ... 259 9.5 Labeling ...260 9.5.1 Glued-On Labels ...260
9.5.3 In-Mold Labels ...260 9.5.4 Sleeve Labels ... 261 9.5.5 Holographic Labels ... 261 9.6 Coding ... 262 9.6.1 Bar Codes ... 263 9.6.2 RFID... 265 References ... 268
Chapter 10 Food Packaging Closures and Sealing Systems ... 271
10.1 Closures for Glass and Plastic Containers ... 271
10.1.1 Closure Functions ... 271
10.1.2 Closure Construction ... 272
10.1.3 Food Container Closures ... 272
10.1.3.1 Closures to Retain Internal Pressure ... 273
10.1.3.2 Closures to Contain and Protect Contents ... 274
10.1.3.3 Closures to Maintain Vacuum inside Container ... 277
10.1.3.4 Closures to Secure Contents inside Container ... 277
10.2 Heat Sealing ... 278 10.2.1 Conductance Sealing ... 279 10.2.2 Impulse Sealing ...280 10.2.3 Dielectric Sealing ... 281 10.2.4 Induction Sealing ... 282 10.2.5 Ultrasonic Sealing ... 283
10.2.6 Hot-Wire and Hot-Knife Sealing ...284
10.2.7 Testing of Heat Seals ...284
10.3 Peelable Seals ... 286
10.3.1 Adhesive Peel ... 286
10.3.2 Cohesive Peel ... 286
10.3.3 Delamination Peel ... 288
10.3.4 Heat Seal Coatings ... 288
10.3.5 Seal Interface Temperature ... 289
10.3.6 Nanocomposite Heat Sealants ... 289
10.4 Cold Seals ... 290
References ... 290
Chapter 11 Deteriorative Reactions in Foods ... 293
11.1 Introduction ... 293
11.2 Deteriorative Reactions in Foods ... 294
11.2.1 Enzymic Reactions ... 294 11.2.2 Chemical Reactions ... 295 11.2.2.1 Sensory Quality ... 295 11.2.2.2 Nutritional Quality... 298 11.2.3 Physical Changes ... 299 11.2.4 Biological Changes ...300 11.2.4.1 Microbiological ...300 11.2.4.2 Macrobiological ...304
11.3 Rates of Deteriorative Reactions ...307
11.3.1 Zero-Order Reactions ... 308
11.3.3 Microbial Growth and Destruction ... 312
11.3.3.1 Microbial Growth ... 312
11.3.3.2 Microbial Destruction ... 313
11.4 Intrinsic Factors Controlling the Rates of Deteriorative Reactions ... 314
11.4.1 Water Activity ... 314
11.4.1.1 Definitions... 314
11.4.1.2 Isotherms ... 314
11.4.1.3 Water Activity and Food Stability ... 317
11.4.2 Oxidation-Reduction Potential ... 320
11.5 Extrinsic Factors Controlling the Rates of Deteriorative Reactions ... 320
11.5.1 Temperature ... 320 11.5.1.1 Linear Model ... 321 11.5.1.2 Arrhenius Relationship ... 321 11.5.1.3 Temperature Quotient ... 322 11.5.1.4 Bělerádek Function ...324 11.5.2 Gas Atmosphere ... 324 11.5.3 Light ... 325 References ... 326
Chapter 12 Shelf Life of Foods ... 329
12.1 Definitions ... 329
12.2 Shelf Life Determination ... 331
12.2.1 Introduction ... 331
12.2.2 Critical Descriptors and Indices of Failure ... 332
12.2.3 Cutoff Point ... 333
12.2.4 Influence of Packaging Material ... 334
12.3 Determining Shelf Life from the Product Side ... 334
12.3.1 Product Characteristics ... 334
12.3.1.1 Perishability ... 334
12.3.1.2 Bulk Density ... 335
12.3.1.3 Concentration Effects ... 335
12.3.2 Package Properties ... 336
12.3.2.1 Water Vapor Transfer ... 336
12.3.2.2 Gas and Odor Transfer ... 341
12.3.2.3 Light Transmission ... 343 12.3.2.4 Package Dimensions ...344 12.3.2.5 Package/Product Interactions ...344 12.3.3 Distribution Environment ... 345 12.3.3.1 Climatic ... 345 12.3.3.2 Physical ... 351
12.4 Predicting Microbial Shelf Life ... 351
12.5 Accelerated Shelf Life Testing ... 354
12.5.1 Basic Principles ... 354
12.5.2 ASLT Procedures ... 356
12.5.3 Examples of ASLT Procedures ... 357
12.5.3.1 Dehydrated Products... 357
12.5.3.2 Frozen Foods ... 357
12.5.3.3 Canned Foods ... 358
12.5.3.5 Oxygen-Absorbing Package ... 358
12.5.3.6 Long-Duration Spaceflight ... 359
12.5.4 Problems in the Use of ASLT Conditions ... 359
12.6 Determining Shelf Life from the Consumer Side ... 360
12.7 Shelf Life Devices ... 362
12.8 Some Cautionary Advice ... 363
References ... 363
Chapter 13 Aseptic Packaging of Foods ... 367
13.1 Introduction ... 367
13.1.1 Historical Development ... 367
13.1.2 Principles of Sterilization ... 368
13.2 Sterilization of Packaging Material Food Contact Surfaces ... 370
13.2.1 Required Count Reduction ... 370
13.2.2 Irradiation ... 371 13.2.2.1 Ionizing Radiation ... 371 13.2.2.2 Pulsed Light ... 371 13.2.2.3 UV-C Radiation ... 371 13.2.2.4 Plasma ... 371 13.2.3 Heat ... 372 13.2.3.1 Saturated Steam ... 372 13.2.3.2 Superheated Steam ... 372 13.2.3.3 Hot Air ... 372
13.2.3.4 Hot Air and Steam ... 372
13.2.3.5 Extrusion ... 372
13.2.4 Chemical Treatments... 373
13.2.4.1 Hydrogen Peroxide ... 373
13.2.4.2 Peracetic Acid ... 374
13.2.5 Verification of Sterilization Processes ... 374
13.3 Aseptic Packaging Systems ... 374
13.3.1 Carton Systems ... 374 13.3.1.1 Form-Fill-Seal Cartons ... 375 13.3.1.2 Prefabricated Cartons ... 376 13.3.2 Can Systems ... 377 13.3.3 Bottle Systems ... 378 13.3.3.1 Glass ... 378 13.3.3.2 Plastics ... 378
13.3.4 Sachet and Pouch Systems ... 379
13.3.4.1 Form-Fill-Seal Systems ... 379
13.3.4.2 Bag-in-Box System ... 380
13.3.4.3 Lay-Flat Tubing ... 380
13.3.5 Cup Systems ... 380
13.3.5.1 Preformed Plastic Cups ... 380
13.3.5.2 Form-Fill-Seal Cups ... 381
13.4 Integrity Testing of Aseptic Packages ... 381
Chapter 14 Packaging of Microwavable Foods ... 383
14.1 Introduction ... 383
14.2 Basic Principles ... 383
14.2.1 Microwave Oven Operation ... 383
14.2.2 Microwave Heating Mechanisms ... 385
14.2.2.1 Dipole Polarization ... 386 14.2.2.2 Ionic Conductivity ... 386 14.2.3 Dielectric Properties ... 387 14.2.4 Energy Conversion ... 387 14.2.5 Penetration of Microwaves ... 390 14.2.6 Nonuniform Heating ... 391
14.3 Effect of Food Product ... 392
14.4 Packaging ... 392
14.4.1 Transparent Materials... 392
14.4.2 Absorbent Materials ... 393
14.4.3 Shielding and Field Modification ... 395
14.4.4 Doneness Indicators ... 396
14.4.5 Testing Methods and Safety ... 396
14.5 Conclusion ... 397
References ... 397
Chapter 15 Active and Intelligent Packaging... 399
15.1 Historical Development ... 399
15.2 Definitions ...400
15.2.1 Active Packaging ...400
15.2.2 Intelligent Packaging ...402
15.3 Active Packaging Systems ...403
15.3.1 Sachets and Pads ...403
15.3.1.1 O2 Absorbers ...403
15.3.1.2 CO2 Absorbers/Emitters ...405
15.3.1.3 Ethylene Absorbers ...405
15.3.1.4 Ethanol Emitters ...406
15.3.1.5 Moisture Absorbers ...406
15.3.2 Active Packaging Materials ...406
15.3.2.1 O2-Absorbing Materials ...406
15.3.2.2 Ethylene Adsorbers ...408
15.3.2.3 Antioxidant Packaging ...408
15.3.2.4 Antimicrobial Packaging ...408
15.3.2.5 Flavor/Odor Absorbers and Releasers ... 411
15.3.2.6 Microwave Susceptors ... 411
15.3.3 Self-Heating and Self-Cooling Packages ... 412
15.3.4 Changing Gas Permeability ... 412
15.3.5 Widgets ... 413
15.4 Intelligent Packaging ... 414
15.4.1 Indicating Product Quality ... 414
15.4.1.1 Quality or Freshness Indicators ... 414
15.4.1.3 Gas Concentration Indicators ... 418
15.4.1.4 Radio Frequency Identification ... 420
15.4.1.5 Biosensors ... 421
15.4.2 Providing More Convenience ... 422
15.4.2.1 Thermochromic Inks ... 422
15.4.2.2 Microwave Doneness Indicators ... 422
15.4.3 Providing Protection against Theft, Counterfeiting and Tampering ....423
15.5 Safety and Regulatory Issues ... 424
15.6 Conclusions ... 425
References ... 425
Chapter 16 Modified Atmosphere Packaging ... 429
16.1 Introduction ... 429
16.1.1 Definitions ... 429
16.1.2 History of MAP ... 430
16.2 Principles ... 431
16.3 Gases Used in MAP ... 433
16.3.1 Carbon Dioxide ... 433 16.3.2 Oxygen ... 434 16.3.3 Nitrogen ... 434 16.3.4 Carbon Monoxide ... 434 16.3.5 Noble Gases ... 435 16.3.6 Gas Mixtures ... 435
16.4 Methods of Creating MA Conditions ... 436
16.4.1 Passive MA ... 436
16.4.2 Active MA ... 436
16.5 Equipment for MAP ... 437
16.5.1 Form-Fill-Seal Machines ... 437
16.5.2 Chamber Machines ... 437
16.5.3 Snorkel Machines ... 437
16.6 Packaging for MAP Applications ... 437
16.7 Microbiology of MAP ... 438
16.8 Safety of MAP ...440
16.9 Refrigerated, Pasteurized Foods with Extended Durability and Sous Vide ... 441
16.10 Applications of MAP ... 442
References ... 443
Chapter 17 Packaging of Flesh Foods ...445
17.1 Introduction ... 445
17.2 Red Meat ... 445
17.2.1 Color of Red Meat ... 445
17.2.1.1 Introduction ... 445
17.2.1.2 Myoglobin Pigments ... 445
17.2.1.3 Role of Oxygen ...446
17.2.1.4 Color Intensity ... 449
17.2.1.5 Role of Carbon Dioxide and Carbon Monoxide ... 450
17.2.1.6 Lighting... 451
17.2.1.7 Effect of Temperature ... 451
17.2.2 Microbiology of Red Meat ... 451
17.2.2.1 Introduction ... 451
17.2.2.2 Effect of Temperature ... 452
17.2.2.3 Effect of Gaseous Atmosphere ... 452
17.2.3 Lipid Oxidation ... 454
17.2.4 Vacuum Packaging of Fresh Meat ... 454
17.2.4.1 Vacuum Packaging Systems ... 455
17.2.4.2 Shelf Life of Vacuum Packaged Red Meats ... 458
17.2.5 Modified Atmosphere Packaging of Fresh Meat ... 459
17.2.5.1 High Oxygen MAP ...460
17.2.5.2 Low Oxygen MAP ... 461
17.2.5.3 Ultra Low Oxygen MAP ... 461
17.2.6 Packaging of Frozen and Restructured Meats ... 462
17.3 Cured and Cooked Meats ... 463
17.4 Poultry ... 465
17.5 Seafood ... 467
17.5.1 Types of Spoilage ... 467
17.5.2 Vacuum and Modified Atmosphere Packaging ... 469
17.5.3 Safety Aspects of Packaged Seafood ... 471
References ... 473
Chapter 18 Packaging of Horticultural Products ... 477
18.1 Introduction ... 477
18.2 Postharvest Physiology ... 477
18.2.1 Respiration ... 477
18.2.1.1 Internal Factors Affecting Respiration ... 479
18.2.1.2 External Factors Affecting Respiration ... 479
18.2.2 Transpiration ... 482
18.2.2.1 Introduction ... 482
18.2.2.2 Factors Influencing Transpiration ... 482
18.2.3 Postharvest Decay ... 483
18.3 Modified Atmosphere Packaging of Fresh Horticultural Produce ... 483
18.3.1 Introduction ... 483
18.3.2 Factors Affecting MAP ...484
18.3.2.1 Resistance to Diffusion ... 485
18.3.2.2 Respiration ... 486
18.3.2.3 Temperature ... 486
18.3.3 Methods of Creating MA Conditions ... 487
18.3.4 Design of MAPs ... 487
18.3.4.1 General Concepts ... 487
18.3.4.2 Developing a Predictive Model ... 489
18.4 Packaging of Horticultural Products ... 494
18.4.1 Fresh and Minimally Processed Horticultural Produce ... 494
18.4.1.1 Introduction ... 494
18.4.1.2 Packaging Materials ... 495
18.4.1.3 Safety of MAP Produce ... 498
18.4.2 Frozen ... 501
18.4.3 Canned ... 502
18.4.4 Dehydrated ... 502
18.4.5 Vegetable Oils ... 503
Chapter 19 Packaging of Dairy Products ...509 19.1 Introduction ...509 19.2 Fluid Milk ...509 19.2.1 Pasteurized Milk ...509 19.2.1.1 Effect of Microorganisms ...509 19.2.1.2 Effect of Temperature ... 510 19.2.1.3 Effect of Light ... 511 19.2.1.4 Effect of Gases ... 513 19.2.1.5 Packaging Materials ... 514 19.2.2 UHT Milk ... 516 19.2.2.1 Process Description ... 516 19.2.2.2 Microbiology... 516 19.2.2.3 Nutrition ... 517
19.2.2.4 Biochemical and Physical Aspects ... 518
19.2.2.5 Flavor ... 518
19.2.2.6 Packaging Materials ... 519
19.3 Fermented Products ... 519
19.4 Butter and Spreads ... 521
19.4.1 Composition ... 521
19.4.2 Packaging Requirements ... 522
19.4.2.1 Oxidation ... 522
19.4.2.2 Water Vapor Permeability ... 524
19.4.2.3 Odor Permeability ... 524
19.4.2.4 Packaging in Current Use ... 524
19.5 Cheese ... 524
19.5.1 Classification ... 524
19.5.2 Microbiology ... 525
19.5.3 Packaging Requirements ... 525
19.5.3.1 Very Hard and Hard ... 526
19.5.3.2 Semisoft and Soft ... 530
19.5.3.3 Fresh ... 532
19.5.3.4 Processed Cheese and Analogues ... 534
19.6 Milk Powders ... 535
19.6.1 Manufacture and Properties ... 535
19.6.2 Deteriorative Reactions ... 536 19.6.2.1 Oxidation ... 536 19.6.2.2 Browning ... 537 19.6.2.3 Caking... 537 19.6.3 Packaging Requirements ... 537 19.6.3.1 O2 Permeability ... 537
19.6.3.2 Water Vapor Permeability ... 537
19.6.3.3 Light ... 538 19.6.4 Packaging Materials ... 538 19.6.4.1 Metal Cans ... 538 19.6.4.2 Laminates ... 539 19.6.4.3 Fiber Cans ... 539 19.6.5 Packaging Techniques ... 539 19.6.5.1 Gas Packing ... 539 19.6.5.2 Vacuum Packaging ...540 References ...540
Chapter 20 Packaging of Cereals, Snack Foods and Confectionery... 545 20.1 Introduction ... 545 20.2 Grains ... 545 20.2.1 Wheat ... 545 20.2.2 Flour ...546 20.2.3 Rice... 547 20.3 Breakfast Cereals... 547 20.3.1 Manufacture ... 547 20.3.2 Indices of Failure ... 548 20.3.3 Packaging ... 548 20.3.3.1 Loss of Crispness ... 548 20.3.3.2 Lipid Oxidation ... 549 20.3.3.3 Loss of Vitamins ... 550 20.3.3.4 Mechanical Damage ... 550 20.3.3.5 Loss of Flavor ... 550 20.4 Pastas ... 550 20.4.1 Dried Pasta ... 551 20.4.2 Fresh Pasta ... 551 20.4.3 Noodles ... 552 20.5 Bakery Products ... 554 20.5.1 Bread ... 554 20.5.1.1 Manufacture ... 554 20.5.1.2 Indices of Failure ... 555 20.5.1.3 Packaging ... 557
20.5.2 Biscuits, Cookies and Crackers ... 560
20.5.2.1 Manufacture ... 560
20.5.2.2 Indices of Failure ... 560
20.5.2.3 Packaging ... 563
20.6 Snack Foods ...564
20.6.1 Fried Snack Foods ...564
20.6.1.1 Manufacture ...564
20.6.1.2 Indices of Failure ...564
20.6.1.3 Packaging ... 565
20.6.2 Extruded and Puffed Snacks ... 567
20.6.2.1 Manufacture ... 567
20.6.2.2 Indices of Failure ... 568
20.6.2.3 Packaging ... 568
20.6.3 Fruit-Based Snacks ... 569
20.7 Confectionery ... 569
20.7.1 Sugar Confectionery (Candy) ... 569
20.7.1.1 Manufacture ... 569 20.7.1.2 Indices of Failure ... 570 20.7.1.3 Packaging ... 571 20.7.2 Chocolate ... 572 20.7.2.1 Manufacture ... 572 20.7.2.2 Indices of Failure ... 572 20.7.2.3 Packaging ... 572 References ... 573
Chapter 21 Packaging of Beverages... 577 21.1 Introduction ... 577 21.2 Water ... 577 21.2.1 Introduction ... 577 21.2.2 Indices of Failure ... 578 21.2.3 Packaging ... 579
21.3 Carbonated Soft Drinks ... 580
21.3.1 Manufacture ... 580 21.3.2 Indices of Failure ... 581 21.3.3 Packaging ... 581 21.3.3.1 Glass ... 581 21.3.3.2 Metal ... 581 21.3.3.3 Plastics ... 582 21.4 Coffee ... 583 21.4.1 Manufacture ... 583 21.4.2 Indices of Failure ... 584 21.4.3 Packaging ... 585
21.4.3.1 Roasted Whole Beans ... 585
21.4.3.2 Roasted and Ground Coffee ... 586
21.4.3.3 Instant Coffee ... 588 21.5 Tea ... 589 21.5.1 Manufacture ... 589 21.5.1.1 Black Tea ... 589 21.5.1.2 Green Tea ... 589 21.5.2 Indices of Failure ... 589 21.5.2.1 Black Tea ... 589 21.5.2.2 Green Tea ... 589 21.5.3 Packaging ... 590 21.6 Juices ... 591 21.6.1 Manufacture ... 591 21.6.2 Indices of Failure ... 591 21.6.3 Packaging ... 592 21.7 Beer ... 594 21.7.1 Manufacture ... 594 21.7.2 Indices of Failure ... 594 21.7.3 Packaging ... 595 21.7.3.1 Glass ... 595 21.7.3.2 Metal ... 596 21.7.3.3 Plastics ... 597 21.8 Wine ... 598 21.8.1 Introduction ... 598 21.8.2 Classification ... 598 21.8.3 Winemaking ... 598 21.8.4 Indices of Failure ... 599 21.8.5 Packaging ... 599 21.8.5.1 Glass ... 599 21.8.5.2 Plastics ... 601 21.8.5.3 Metal ...602
21.8.5.4 Laminated Paperboard Cartons ...602
Chapter 22 Legislative and Safety Aspects of Food Packaging ...607
22.1 Introduction ...607
22.1.1 Package Selection Criteria...607
22.1.2 Migration ...607
22.2 Regulatory Considerations ...609
22.2.1 General Requirements ...609
22.2.2 United States of America ... 611
22.2.3 European Union ... 618
22.2.3.1 Background ... 618
22.2.3.2 Directives ... 618
22.3 Plastics Packaging ... 622
22.3.1 Vinyl Chloride Monomer ... 622
22.3.2 Styrene Monomer ... 623
22.3.3 Acrylonitrile Monomer ... 623
22.3.4 Plasticizers ... 624
22.3.4.1 Phthalate and Adipate Esters ... 624
22.3.4.2 Acetyltributyl Citrate ... 625
22.3.4.3 Epoxidized Soy Bean Oil ... 626
22.3.5 Antioxidants ... 626 22.4 Metal Packaging ... 627 22.4.1 Tin ... 627 22.4.2 Lead ... 628 22.4.3 Aluminum ... 628 22.4.4 Chromium ... 629 22.4.5 Silver ... 629
22.4.6 Epoxy Resin Coatings ... 630
22.5 Paper Packaging ... 631
22.5.1 Dioxins ... 631
22.5.2 Benzophenone ... 632
22.5.3 Isopropylthioxanthone ... 633
22.5.4 Mineral Oil Saturated Hydrocarbons ... 633
22.5.5 Miscellaneous ... 634
22.6 Glass Packaging ... 636
22.7 Taints and Off-Flavors ... 636
22.7.1 Solvents ... 636 22.7.2 Residual Monomers ... 637 22.7.3 Organohalogens ... 637 22.7.4 Miscellaneous ...640 22.8 Traceability ...640 References ...640
Chapter 23 Food Packaging and Sustainability ... 645
23.1 Introduction ... 645
23.1.1 What Is Waste? ...646
23.2 Waste Management Options ... 647
23.2.1 Hierarchy of Waste Management ... 647
23.2.2 Source Reduction ...648
23.2.3 Recycling ... 649
23.2.3.1 Closed-Loop Recycling ... 649
23.2.3.3 Materials Recovery Facility... 650 23.2.3.4 Benefits ... 650 23.2.3.5 Technologies ... 653 23.2.4 Composting ... 656 23.2.5 Thermal Treatment ... 657 23.2.6 Landfill ... 658
23.3 Life Cycle Assessment ...660
23.3.1 Goal Definition and Scoping ... 661
23.3.2 Life Cycle Inventory ... 661
23.3.3 Life Cycle Impact Assessment ... 662
23.3.4 Life Cycle Interpretation ... 662
23.3.5 Limitations of LCA ... 662
23.3.6 Uses of LCAs ... 663
23.3.7 Tools for LCA ...664
23.3.8 Carbon Footprinting ...664
23.4 Packaging and Environmental Policies ...666
23.4.1 United States ...666
23.4.1.1 Container Deposits ...666
23.4.1.2 Extended Product Responsibility ... 667
23.4.2 Europe ... 667
23.4.2.1 Producer Responsibility ... 667
23.4.2.2 German Packaging Ordinance... 668
23.4.2.3 Packaging and Packaging Waste Directive ... 668
23.5 Packaging and Sustainability ... 669
23.5.1 Sustainable Development ... 669
23.5.2 Sustainable Packaging ... 670
23.5.3 Sustainability Reporting ... 672
23.5.4 Supply Chain Management ... 672
References ... 673
1
1
Introduction to Food
Packaging
1.1 INTRODUCTION
In today’s society, packaging is pervasive and essential. It surrounds, enhances and protects the goods we buy, from processing and manufacturing, through handling and storage, to the final consumer. Without packaging, materials handling would be a messy, inefficient and costly exercise and modern consumer marketing would be virtually impossible. The packaging sector represents about 2% of the gross national product (GNP) in developed countries, and about half of all packaging is used to package food.
The historical development of packaging has been well documented elsewhere and will not be described in depth here. However, an appreciation of the origins of packaging materials and knowl-edge of the early efforts in package development can be both instructive and inspirational and for this reason they are discussed briefly in the appropriate chapters. Suffice it to say that the highly sophisticated packaging industries that characterize modern society today are far removed from the simple packaging activities of earlier times.
Very few books can lay claim to be the first to expound or develop a particular area, and the pres-ent work is no exception. An increasing number of books have appeared over the past few years with the words “food” and “packaging” in their titles, and several are listed at the end of this chapter. The whole field of food science and technology has undergone tremendous development over the last 30 years, and this has been reflected in a plethora of books, many of which address quite specific sub-ject areas (Robertson 2009a, b). In addition, there has also been a significant increase in the number of papers dealing with food and packaging published in the scientific literature, and many of them are referenced at the end of the appropriate chapters.
Food packaging lies at the very heart of the modern food industry, and successful food packaging technologists must bring to their professional duties a wide-ranging background drawn from a multi-tude of disciplines. The interdisciplinary nature of food packaging is evident from the chapter headings in this book. Sufficient material has been included in the text for it to stand alone as a textbook for undergraduate and graduate students who are taking a two-semester course in food packaging. The ear-lier editions of this book were also widely used in industry, often by those with no formal education in food science and technology. Therefore, brief descriptions of the basic composition and manufacturing processes used for a wide range of foods are included, with an emphasis on those aspects that influence package choice and performance. Key references are given at the end of each chapter so that those who wish to pursue particular aspects in more depth will have some guidance to start them on their way.
1.2 DEFINITIONS
Despite the important and key role that packaging plays, it is often regarded as a necessary evil or an unnecessary cost. Furthermore, in the view of many consumers, packaging is, at best, somewhat superfluous, and, at worst, a serious waste of resources and an environmental menace. Such views arise because the functions that packaging has to perform are either unknown or not considered in full. By the time most consumers come into contact with a package, its job, in many cases, is almost over, and it is perhaps understandable that the view that excessive packaging has been used has gained some credence.
Packaging has been defined as a socio-scientific discipline that operates in society to ensure the delivery of goods to the ultimate consumer of those goods in the best condition intended for their
use (Lockhart, 1997). The now-defunct Packaging Institute International (Glossary of Packaging Terms, 1988) defined packaging as the enclosure of products, items or packages in a wrapped pouch, bag, box, cup, tray, can, tube, bottle or other container form to perform one or more of the following functions: containment, protection, preservation, communication, utility and performance. If the device or container performed one or more of these functions, it was considered a package.
Other definitions of packaging include a coordinated system of preparing goods for transport, distribution, storage, retailing and end use, a means of ensuring safe delivery to the ultimate con-sumer in sound condition at optimum cost and a techno-commercial function aimed at optimizing the costs of delivery while maximizing sales (and, hence, profits) (Coles and Kirwan, 2011).
It is important to distinguish between the words “package,” “packaging” and “packing.” The package is the physical entity that contains the product. Packaging was defined in the previous para-graphs and, in addition, it is also a discipline as in “Packaging Technologist.” The verb “packing” can be defined as the enclosing of an individual item (or several items) in a package or container.
A distinction is usually made between the various “levels” of packaging. A primary package is one that is in direct contact with the contained product. It provides the initial, and usually the major, protective barrier. Examples of primary packages include metal cans, paperboard cartons, glass bottles and plastic pouches. It is frequently only the primary package that the consumer purchases at retail outlets. This book will confine itself to a consideration of the primary package.
A secondary package, for example, a corrugated case or box, contains a number of primary pack-ages. It is the physical distribution carrier and is increasingly designed so that it can be used in retail outlets for the display of primary packages, in which case it is referred to as shelf ready. A tertiary package is made up of a number of secondary packages, with the most common example being a stretch-wrapped pallet of corrugated cases. In interstate and international trade, a quaternary pack-age is frequently used to facilitate the handling of tertiary packpack-ages. This is generally a metal con-tainer up to 40 m in length that can hold many pallets and is intermodal in nature, that is, it can be transferred to or from ships, trains and flatbed trucks by giant cranes. Certain containers are also able to have their temperature, humidity and gas atmosphere controlled; this is necessary in particular situations such as the transportation of frozen foods, chilled meats and fresh fruits and vegetables.
Although the aforementioned definitions cover the basic role and form of packaging, it is neces-sary to discuss in more detail the functions of packaging and the environments where the package must perform those functions.
1.3 FUNCTIONS OF PACKAGING
Packaging performs a series of disparate tasks: it protects its contents from contamination and spoilage, makes it easier to transport and store goods and provides uniform measuring of contents (Hine, 1995). By allowing brands to be created and standardized, it makes advertising meaningful and large-scale distribution possible. Special kinds of packages with dispensing caps, sprays and other convenience features make products easier to use. Packages serve as symbols of their contents and a way of life and, just as they can very powerfully communicate the satisfaction a product offers, they are equally potent symbols of wastefulness once the product is gone.
Four primary functions of packaging have been identified: containment, protection, convenience and communication. These four functions are interconnected and all must be assessed and consid-ered simultaneously in the package development process.
1.3.1 CONTAINMENT
This function of packaging is so obvious as to be overlooked by many, but, with the exception of large, discrete products, all other products must be contained before they can be moved from one place to another. The “package,” whether it is a bottle of cola or a bulk cement rail wagon, must contain the product to function successfully. Without containment, product loss and pollution would be widespread.
The containment function of packaging makes a huge contribution to protecting the environment from the myriad of products that are moved from one place to another on numerous occasions each day in any modern society. Faulty packaging (or under-packaging) could result in major pollution of the environment. Even today, the containment function of packaging is not always addressed satis-factorily, as evidenced by the number of packaged foods that leak their contents, especially around the closures and seals.
1.3.2 PROTECTION
This is often regarded as the primary function of the package: to protect its contents from outside environmental influences such as water, water vapor, gases, odors, microorganisms, dust, shocks, vibrations and compressive forces.
For the majority of foods, the protection afforded by the package is an essential part of the pres-ervation process. For example, aseptically packaged milk and fruit juices in paperboard cartons only remain aseptic for as long as the package provides protection. Likewise, vacuum-packaged meat will not achieve its desired shelf life if the package permits O2 to enter. In general, once the integrity of the package is breached, the product is no longer preserved.
Packaging also protects or conserves much of the energy expended during the production and processing of the product. For example, to produce, transport, sell and store 1 kg of bread requires 15.8 MJ (megajoules) of energy. This energy is required in the form of transport fuel, heat, power and refrigeration in farming and milling the wheat, baking and retailing the bread, and in distribut-ing both the raw materials and the finished product. To manufacture the low density polyethylene (LDPE) bag to package a 1 kg loaf of bread requires 1.4 MJ of energy. This means that each unit of energy in the packaging protects 11 units of energy in the product. While eliminating the packaging might save 1.4 MJ of energy, it would also lead to spoilage of the bread and a consequent waste of 15.8 MJ of energy.
1.3.3 CONVENIENCE
Modern industrialized societies have brought about tremendous changes in lifestyles and the pack-aging industry has had to respond to those changes. Now an ever-increasing number of households are single person, many couples either delay having children or opt not to at all and a greater per-centage of women are in the workforce than ever before.
All these changes, as well as other factors such as the trend toward “grazing” (i.e., eating snack-type meals frequently and on the run rather than regular meals), the demand for a wide variety of food and drink at outdoor functions such as sports events, and increased leisure time, have created a demand for greater convenience in household products. Products designed to increase convenience include foods that are preprepared and can be cooked or reheated in a very short time, preferably without removing them from their primary package, and sauces, dressings and condiments that can be applied simply through aerosol or pump-action packages that minimize mess. Thus, packaging plays an important role in meeting the demands of consumers for convenience. Convenient packages promote sales.
Two other aspects of convenience are important in package design. One of these can best be described as the apportionment function of packaging. In this context, the package functions by reducing the output from industrial production to a manageable, desirable “consumer” size. Thus, a vat of wine is “apportioned” into 750 mL bottles; a churn of butter is “apportioned” by packing into 25 g minipats and a batch of ice cream is “apportioned” by filling into 2 L plastic tubs.
Put simply, the large-scale production of products that characterizes modern society could not succeed without the apportionment function of packaging. The relative cheapness of consumer products is largely because of their production on an enormous scale and the resultant savings. But, as the scale of production has increased, so too has the need for effective methods of apportioning the product into consumer-sized dimensions.
For a product that is not entirely consumed when the package is first opened, the package should be resealable and retain the quality of the product until completely used. Furthermore, the package should contain a portion size that is convenient for the intended consumers; a package that contains so much product that it would deteriorate before being completely consumed clearly contains too large a portion.
An associated aspect is the shape (relative proportions) of the primary package with regard to consumer convenience (e.g., easy to hold, open and pour as appropriate) and efficiency in building into secondary and tertiary packages. In the movement of packaged goods in interstate and inter-national trade, it is clearly inefficient to handle each primary package individually. Here, packaging plays another very important role in permitting primary packages to be unitized into secondary packages (e.g., placed inside a corrugated case) and secondary packages to be unitized into a tertiary package (e.g., a stretch-wrapped pallet). This unitizing activity can be carried a stage further to pro-duce a quaternary package (e.g., a container that is loaded with several pallets). If the dimensions of the primary and secondary packages are optimal, then the maximum space available on the pallet can be used. As a consequence of this unitizing function, materials handling is optimized since only a minimal number of discrete packages or loads need to be handled.
1.3.4 COMMUNICATION
There is an old saying that “a package must protect what it sells and sell what it protects.” It may be old, but it is still true; a package functions as a “silent salesman” (Judd et al., 1989). The modern methods of consumer marketing would fail were it not for the messages communicated by the package. The ability of consumers to instantly recognize products through distinctive shapes, branding and label-ing enables supermarkets to function on a self-service basis. Without this communication function (i.e., if there were only plain packs and standard package sizes), shopping in a supermarket would be a lengthy, frustrating nightmare as consumers attempted to make purchasing decisions without the numerous visual clues provided by the graphics and the distinctive shapes of the packaging.
Other communication functions of the package are equally important. Today, the widespread use of modern scanning equipment at retail checkouts relies on all packages displaying a universal product code (UPC) that can be read accurately and rapidly. Nutritional information on the outside of food packages has become mandatory in many countries. Smart labels that can be read by camera phones are also appearing on packages and these are discussed in Chapter 9.
But it is not only in the supermarket that the communication function of packaging is important. Warehouses and distribution centers would (and sometimes do) become chaotic if secondary and tertiary packages lack labels or carry incomplete details.
When international trade is involved and different languages are spoken, the use of unambiguous, readily understood symbols on the package is imperative. UPCs are also frequently used in warehouses where handheld barcode readers linked to a computer make stocktaking quick and efficient. Today, the use of RFID tags attached to secondary and tertiary packages is revolutionizing the supply chain.
1.4 PACKAGE ENVIRONMENTS
The packaging has to perform its functions in three different environments (Lockhart, 1997). Failure to consider all three environments during package development will result in poorly designed packages, increased costs, consumer complaints and even avoidance or rejection of the product by the customer.
1.4.1 PHYSICAL ENVIRONMENT
This is the environment in which physical damage can be caused to the product. It includes shocks from drops, falls and bumps, damage from vibrations arising from transportation modes including road, rail, sea and air and compression and crushing damage arising from stacking during transpor-tation or storage in warehouses, retail outlets and the home.
1.4.2 AMBIENT ENVIRONMENT
This is the environment that surrounds the package. Damage to the product can be caused as a result of gases (particularly O2), water and water vapor, light (particularly UV radiation) and temperature, as well as microorganisms (bacteria, fungi, molds, yeasts and viruses) and macro-organisms (rodents, insects, mites and birds) that are ubiquitous in many warehouses and retail outlets. Contaminants in the ambient environment such as exhaust fumes from auto-mobiles and dust and dirt can also find their way into the product unless the package acts as an effective barrier.
1.4.3 HUMAN ENVIRONMENT
This is the environment in which the package interacts with people, and designing packages for this environment requires knowledge of the variability of consumers’ capabilities including vision, strength, weakness, dexterity, memory and cognitive behavior. It includes knowledge of the results of human activity such as liability, litigation, legislation and regulation. Because one of the func-tions of the package is to communicate, it is important that the messages are clearly received by consumers. In addition, the package must contain information required by law such as nutritional content and net weight.
1.5 FUNCTIONS/ENVIRONMENT GRID
The functions of packaging and the environments where the package has to perform can be laid out in a two-way matrix or grid as shown in Figure 1.1 (Lockhart, 1997). Anything that is done in packaging can be classified and located in one or more of the 12 function/environment cells. The grid provides a methodical yet simple way of evaluating the suitability of a particular package design before it is actually adopted and put into use. As well, the grid serves as a useful aid when evaluating existing packaging.
Separate grids can be laid out for distribution packaging analysis, corrugated packaging analysis, legal/regulatory impact or for any mix of package-related concepts that are of interest. In a further refinement of the grid, a third dimension has been suggested to represent the intensity of the interac-tions in each cell.
Protection F unction s Containment Convenience Communication Environments
Physical Ambient Human
FIGURE 1.1 Functions/environments grid for evaluating package performance. (From Lockhart, H.E.,
Missing from the grid is an opportunity to evaluate the environmental impacts of the package. This aspect has now become such an important element in package design that it should be con-sidered fully in its own right and in addition to the evaluation carried out using the grid shown in Figure 1.1; it is the subject of the last chapter in this book as part of the broader topic of sustainability.
Knowledge of the functions of packaging and the environments where it has to perform will lead to the optimization of package design and the development of real, cost-effective packaging. Despite the several functions that a package must perform, this book focuses almost exclusively on the pro-tective and containment functions of the primary package and possible food and package interactions in relation to the ambient environment. Package performance in the physical environment is usually considered under the heading of packaging engineering (Hanlon et al., 1998). The communication function of package performance in the human environment is properly the major concern of those with a primary interest in marketing and advertising. For those focusing on the convenience-in-use aspects of packaging, books in the area of consumer ergonomics are the best source of information.
The standard ISO 11156 provides a framework for design and evaluation of packages so that more people, including persons from different cultural and linguistic backgrounds, older persons and persons whose sensory, physical and cognitive functions have been weakened or have allergies, can appropriately identify, handle and use the contents. It considers varying aspects of the packaged product life cycle from identification of the product, through purchase and use of the product to the separation and disposal of the package. However, ISO 11156 does not apply to dimensions, materi-als, manufacturing methods or evaluation methods of individual packages.
In recent years, greater attention has been given to the difficulties faced by an ageing population in accessing packaging. The openability of packaging is of increasing concern, with a survey of consum-ers aged over 60 finding that more than 50% of respondents had problems very often or frequently in opening peelable induction seals, lug closures and continuous thread closures (Duizer et al., 2009). If products and their packaging are designed with the weakest target consumer in mind, then the entire target population will be able to physically access the package and product. Yoxall et al. (2010) showed that larger-diameter jars (85 mm) required much higher opening forces than smaller ones (75 mm and below). Smaller jars required lower opening torques, although the force required to open many jars was still higher than many elderly people are able to generate. The authors noted that fur-ther work is required to more accurately determine the strength of consumers and the forces required to open common items of food packaging. This topic is discussed further in Chapter 10.
The term “biomechanical data” is used to describe quantities relating to motion, position and force, that is, the movements of a person when interacting with a product and the forces acting on the product during such an interaction. A survey of packaging design professionals revealed that biomechanical data were rarely used and inclusive (or universal) design principles were not routinely incorporated into company procedures (Carse et al., 2010). Although there are some stan-dards and methods provided as a guideline for universal design (UD), it does not reflect packaging requirements for consumers. Yiangkamolsing et al. (2010) identified the five principles relevant to UD as (1) convenient, intuitive, simple and safe use; (2) perceptible information; (3) structure and graphic design; (4) easy opening; and (5) equitable use. For each group of UD performance mea-sures, a minimal but relevant set of consumer requirements were identified for flexible packaging that ensures that the flexible packaging designer conforms to UD principles.
1.6 PACKAGING INNOVATION
Innovation has been defined as invention plus exploitation (Roberts, 2007). The invention process covers all efforts aimed at creating new ideas, concepts, devices or processes and getting them to work. The exploitation process includes all stages of commercial development, application and transfer, including the focusing of ideas or inventions toward specific objectives, evaluating those objectives, downstream transfer of research and/or development results and the eventual broad-based utilization, dissemination and diffusion of the technology-based outcomes. Whereas invention is
marked by discovery or a state of new existence (usually in the laboratory or at the bench), innova-tion is marked by first use in manufacturing or in a market.
The patent literature is full of packaging inventions but fewer than 10% will ever be exploited and, thus, qualify as innovations. The process of technological innovation can take as long as 20–30 years according to some studies, but for most industrial product innovations, the duration from initial idea to market is more likely to be 3–8 years (Roberts, 2007). Awareness of customer needs plays a power-ful role in invention and innovation, leading to what is known as “market pull” in contrast to “techno-logical push,” which is less likely to be successful. Mostly, innovation is all about small changes that build on inherent flexibility in existing products or systems. Occasionally, something big happens, and a completely new idea is born that can best be described as a mutation rather than an adaptation.
There are several drivers for packaging innovations. One is the fast-changing social trends and the increasing consumer demand for convenience and safety. Another is growing environmental awareness, while profitability and differentiation are also important for food companies seeking to attract consumer attention. Sustainability will receive increasing attention and a plethora of labels such as carbon footprint and paper from sustainably managed forests will indicate how companies are performing in this area. Because consumers want innovation and value novelty, the packaging industry must continue to innovate or risk stagnation.
An interesting way to view innovations is provided by the Gartner hype cycle (Morris, 2011), introduced in 1995 by technology consulting firm Gartner Research. It characterizes the typi-cal progression of an innovation from overenthusiasm through a period of disillusionment to an eventual understanding of the technology’s relevance and role in a market (see Figure 1.2). The first part of the hype curve begins with an innovation trigger from a potential technology breakthrough or invention. Early proof-of-concept stories and media interest trigger signifi-cant publicity, although often no usable products exist and commercial viability is unproven. This positive hype (mainly by the media and especially the trade press in the case of packag-ing innovations) speculates on the technology’s prospects and is followed by negative hype when the innovation fails to immediately deliver as promised. The message to companies at this stage is not to invest in or adopt a technology just because it is being hyped, nor ignore a technology just because it is not living up to early overexpectations. After a period of disil-lusionment, an eventual understanding of the technology’s relevance and role in a market or domain emerges, driven primarily by performance gains and adoption growth and the release of second- and third-generation products (Fenn and Raskino, 2008). By understanding the hype cycle, it can be ridden more skillfully and investment decisions timed so that the innova-tions adopted stand the best chance of succeeding in the long term.
However, there have been numerous criticisms of the hype cycle, prominent among which are that it is not a cycle, that the outcome does not depend on the nature of the technology itself, that it is not scientific in nature and that it does not reflect changes over time in the speed at which technology develops. Another is that the cycle has no real benefits to the development or marketing of new technologies and merely comments on preexisting trends. Despite these criticisms, it has remained a popular and useful way for companies to evaluate innovations.
In the area of food packaging, smart packaging is still subject to positive hype, together with biobased polymers such as bioPET and bioHDPE. Antimicrobial packaging is also at this early stage but is unlikely to ever reach the plateau of productivity. Biobased polymers such as PLA and PHA are now experiencing negative hype as more companies trial them. Time– temperature indicators, after more than 40 years, have moved up the slope of enlightenment but are unlikely to ever become more than a niche market. The retort pouch is approaching the plateau of pro-ductivity. It is important to remember that the big innovations in food packaging such as MAP and aseptic packaging took 20–30 years before they reached the plateau of productivity.
1.7 FINDING INFORMATION
It has never been simpler to keep up-to-date or find the latest information, provided one has an Internet connection. Although there are various approaches that one can adopt, Google Scholar (www.scholar.google.com) is free and provides a simple way to broadly search for scholarly litera-ture. From one place, you can search across many disciplines and sources: articles, books, theses and abstracts from academic publishers, professional societies, online repositories, universities and other websites. With Google Scholar, you can find relevant work across the world of scholarly research, including where it was published, who it was written by, as well as how often and how recently it has been cited in other scholarly literature.
For example, if you want to read the abstract for any paper listed in the references at the end of each chapter in this book, simply type the title of the paper into Google Scholar. As well as display-ing the abstract, you will also get details of all those who have cited the paper, plus related articles. In this way, it is easy to keep up-to-date with the latest research on a particular topic. The default setting also includes details of any patents that have cited the paper. If you want to find recent papers on a specific topic, select the date range from the dropdown menu under the search box. If you want to search the nonscientific literature such as trade magazines, simply do a general web search.
If you want to read something published in a book, try Google Books. If the book is out of copy-right, or the publisher has given permission, you will be able to see a preview of the book and, in some cases, the entire text online. If it is in the public domain, you are free to download a PDF copy.
REFERENCES
Carse B., Thomson A., Stansfield B. 2010. Use of biomechanical data in the inclusive design process: Packaging design and the older adult. Journal of Engineering Design 21: 289–303.
Coles R., Kirwan M. (Eds.). 2011. Food and Beverage Packaging Technology. Oxford, England: Wiley-Blackwell. Duizer L.M., Robertson T.R., Han J. 2009. Requirements for packaging from an ageing consumer’s
perspec-tive. Packaging Technology and Science 22: 187–197.
E x pecta tions Retort pouch Aseptic packaging Time Don’t join in just because it’s “In”
Antimicrobial packaging
BioPET
Positive hype
Don’t miss out just because it’s “Out” PLA PHA Negative hype Innovation trigger Peak of inflated expectations Trough of disillusionment Slope of enlightenment Plateau of productivity MAP Time-temperature indicators
FIGURE 1.2 Gartner hype cycle characterizing the typical progression of an innovation from overenthusiasm through a period of disillusionment to an eventual understanding of the technology’s relevance and role in a market or domain. (Adapted from Gartner Inc. Used with permission.)
Fenn J., Raskino M. 2008. Mastering the Hype Cycle: How to Choose the Right Innovation at the Right Time. Boston, MA: Harvard Business Press.
Glossary of Packaging Terms. Stamford, CT: The Packaging Institute International, 1988.
Hanlon J.F., Kelsey R.J., Forcinio H.E. 1998. Handbook of Package Engineering, 3rd edn. Boca Raton, FL: CRC Press.
Hine T. 1995. The Total Package: The Evolution and Secret Meanings of Boxes, Bottles, Cans and Tubes. New York: Little, Brown.
Judd D., Aalders B., Melis T. 1989. The Silent Salesman. Singapore: Octogram Design.
Lockhart H.E. 1997. A paradigm for packaging. Packaging Technology and Science 10: 237–252. Morris S.A. 2011. Food and Package Engineering. Chichester, England: Wiley-Blackwell.
Roberts E.B. 2007. Managing invention and innovation. Research Technology Management 50: 35–54. Robertson G.L. 1993. Food Packaging: Principles and Practice. New York: Marcel Dekker.
Robertson G.L. 2006. Food Packaging Principles and Practice, 2nd edn. Boca Raton, FL: CRC Press. Robertson G.L. 2009a. Food packaging. In: Textbook of Food Science and Technology, Campbell-Platt G. (Ed.).
Oxford, England: Blackwell Publishing, pp. 279–298.
Robertson G.L. 2009b. Packaging of food. In: The Wiley Encyclopedia of Packaging Technology, 3rd edn., Yam K.L. (Ed.). New York: John Wiley & Sons, pp. 891–898.
Robertson G.L. (Ed.). 2010. Food Packaging and Shelf Life: A Practical Guide. Boca Raton, FL: CRC Press. Yiangkamolsing C., Bohez E.L.J., Bueren I. 2010. Universal design (UD) principles for flexible packaging
and corresponding minimal customer requirement set. Packaging Technology and Science 23: 283–300. Yoxall A., Langley J., Janson R., Lewis R., Wearn J., Hayes S.A., Bix L. 2010. How wide do you want the jar?:
The effect on diameter for ease of opening for wide-mouth closures. Packaging Technology and Science 21: 61–72.
11
2
Structure and Related
Properties of Plastic Polymers
2.1 INTRODUCTIONThe adjective plastic is derived from the Greek plastikos, meaning easily shaped or deformed. It was first introduced into the English language in the nineteenth century to describe the behavior of the recently discovered cellulose nitrate that behaved like clay when mixed with solvents. The noun “plastics” is often defined in dictionaries as a group of synthetic resinous or other substances that can be molded into any form. From a technical viewpoint, plastics is a generic term for mac-romolecular organic compounds obtained from molecules with a lower molecular weight (MW) or by chemical alteration of natural macromolecular compounds. At some stage of their manufacture, they can be formed to shape by flow, aided in many cases by heat and pressure. The term plastics can be used as a noun, singular or plural, and as an adjective.
The standard terms used for plastics are defined in ASTM D833. Commonly, the word “ plastic” is used to describe the easily deformable state of the material, and the word “plastics” to describe the vast range of materials based on macromolecular organic compounds. This chapter will describe plastics relevant to food packaging, with particular emphasis on their structure and related properties.
The utility of flexible sheet materials depends on the properties of a special kind of molecular structure: long, flexible molecules interlocked into a strong and nonbrittle lattice. These structures are built up by the repeated joining of small basic building blocks called monomers, the result-ing compound beresult-ing called a polymer, derived from the Greek roots meros meanresult-ing parts, and poly meaning many. Differences in the chemical constitution of the monomers, in the structure of the polymer chains and in the interrelationship of the chains determine the different properties of the various polymeric materials.
2.2 HISTORY
Although the chemical nature of polymers (and the fact that they consist of enormous molecules) was not understood until well into the mid-twentieth century, the materials themselves, and the industry based on them, existed long before that (Andrady and Neal, 2009).
Since plastics include compounds obtained by chemical alteration of natural macromolecular compounds, then the earliest example of a plastics material would have to be hard rubber. In 1839 Charles Goodyear, an American inventor, found that rubber heated with sulfur retained its elasticity over a wider temperature range than the raw material and that it had greater resistance to solvents. The rubber–sulfur reaction was termed “vulcanization.” The significance of the discovery of hard rubber lies in the fact that it was the first thermosetting (defined in Section 2.3.1.1) plastics material to be prepared and also the first plastics material that involved a distinct chemical modification of a natural material.
It is generally considered that the development of the plastics industry began in the 1860s. At the International Exhibition of 1862 in London, Alexander Parkes, an English chemist and metallurgist, displayed a new material (which he later modestly called “Parkesine”) that he had made by treating cotton waste with a mixture of nitric and sulfuric acids. This was already a well-known process used for making the explosive called guncotton, but Parkes found that by altering the proportions
