Expert overviews covering the
science and technology of rubber
Volume 16, Number 12, 2005
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33, No.6, 21st March 2000, p.2171-83
EFFECT OF THERMAL HISTORY ON THE RHEOLOGICAL BEHAVIOR OF THERMOPLASTIC POLYURETHANES Pil Joong Yoon; Chang Dae Han
The effect of thermal history on the rheological behaviour of ester- and ether-based commercial thermoplastic PUs (Estane 5701, 5707 and 5714 from B.F.Goodrich) was investigated. It was found that the injection moulding temp. used for specimen preparation had a marked effect on the variations of dynamic storage and loss moduli of specimens with time observed during isothermal annealing. Analysis of FTIR spectra indicated that variations in hydrogen bonding with time during isothermal annealing very much resembled variations of dynamic storage modulus with time during isothermal annealing. Isochronal dynamic temp. sweep experiments indicated that the thermoplastic PUs exhibited a hysteresis effect in the heating and cooling processes. It was concluded that the microphase separation transition or order-disorder transition in thermoplastic PUs could not be determined from the isochronal dynamic temp. sweep experiment. The plots of log dynamic storage modulus versus log loss modulus varied with temp. over the entire range of temps. (110-190C) investigated. 57 refs.
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Location Companies or organisations mentioned Abstract Authors and afﬁliation Source of original article Title
Report 1 Conductive Polymers, W.J. Feast
Report 2 Medical, Surgical and Pharmaceutical Applications of Polymers, D.F. Williams
Report 3 Advanced Composites, D.K. Thomas, RAE, Farnborough.
Report 4 Liquid Crystal Polymers, M.K. Cox, ICI, Wilton. Report 5 CAD/CAM in the Polymer Industry, N.W. Sandland
and M.J. Sebborn, Cambridge Applied Technology. Report 8 Engineering Thermoplastics, I.T. Barrie, Consultant. Report 10 Reinforced Reaction Injection Moulding,
P.D. Armitage, P.D. Coates and A.F. Johnson Report 11 Communications Applications of Polymers,
R. Spratling, British Telecom.
Report 12 Process Control in the Plastics Industry, R.F. Evans, Engelmann & Buckham Ancillaries.
Report 13 Injection Moulding of Engineering Thermoplastics, A.F. Whelan, London School of Polymer Technology. Report 14 Polymers and Their Uses in the Sports and Leisure
Industries, A.L. Cox and R.P. Brown, Rapra Technology Ltd.
Report 15 Polyurethane, Materials, Processing and Applications, G. Woods, Consultant.
Report 16 Polyetheretherketone, D.J. Kemmish, ICI, Wilton. Report 17 Extrusion, G.M. Gale, Rapra Technology Ltd. Report 18 Agricultural and Horticultural Applications of
Polymers, J.C. Garnaud, International Committee for Plastics in Agriculture.
Report 19 Recycling and Disposal of Plastics Packaging, R.C. Fox, Plas/Tech Ltd.
Report 20 Pultrusion, L. Hollaway, University of Surrey. Report 21 Materials Handling in the Polymer Industry,
H. Hardy, Chronos Richardson Ltd.
Report 22 Electronics Applications of Polymers, M.T.Goosey, Plessey Research (Caswell) Ltd.
Report 23 Offshore Applications of Polymers, J.W.Brockbank, Avon Industrial Polymers Ltd.
Report 24 Recent Developments in Materials for Food Packaging, R.A. Roberts, Pira Packaging Division.
Report 25 Foams and Blowing Agents, J.M. Methven, Cellcom Technology Associates.
Report 26 Polymers and Structural Composites in Civil Engineering, L. Hollaway, University of Surrey. Report 27 Injection Moulding of Rubber, M.A. Wheelans,
Report 28 Adhesives for Structural and Engineering Applications, C. O’Reilly, Loctite (Ireland) Ltd. Report 29 Polymers in Marine Applications, C.F.Britton,
Corrosion Monitoring Consultancy.
Report 30 Non-destructive Testing of Polymers, W.N. Reynolds, National NDT Centre, Harwell.
Report 31 Silicone Rubbers, B.R. Trego and H.W.Winnan, Dow Corning Ltd.
Report 32 Fluoroelastomers - Properties and Applications, D. Cook and M. Lynn, 3M United Kingdom Plc and 3M Belgium SA.
Report 33 Polyamides, R.S. Williams and T. Daniels,
Report 34 Extrusion of Rubber, J.G.A. Lovegrove, Nova Petrochemicals Inc.
Report 35 Polymers in Household Electrical Goods, D.Alvey, Hotpoint Ltd.
Report 36 Developments in Additives to Meet Health and Environmental Concerns, M.J. Forrest, Rapra Technology Ltd.
Report 37 Polymers in Aerospace Applications, W.W. Wright, University of Surrey.
Report 38 Epoxy Resins, K.A. Hodd
Report 39 Polymers in Chemically Resistant Applications, D. Cattell, Cattell Consultancy Services.
Report 40 Internal Mixing of Rubber, J.C. Lupton Report 41 Failure of Plastics, S. Turner, Queen Mary College. Report 42 Polycarbonates, R. Pakull, U. Grigo, D. Freitag, Bayer AG. Report 43 Polymeric Materials from Renewable Resources,
J.M. Methven, UMIST.
Report 44 Flammability and Flame Retardants in Plastics, J. Green, FMC Corp.
Report 45 Composites - Tooling and Component Processing, N.G. Brain, Tooltex.
Report 46 Quality Today in Polymer Processing, S.H. Coulson, J.A. Cousans, Exxon Chemical International Marketing. Report 47 Chemical Analysis of Polymers, G. Lawson, Leicester
Report 48 Plastics in Building, C.M.A. Johansson
Report 49 Blends and Alloys of Engineering Thermoplastics, H.T. van de Grampel, General Electric Plastics BV.
Report 50 Automotive Applications of Polymers II, A.N.A. Elliott, Consultant.
Report 51 Biomedical Applications of Polymers, C.G. Gebelein, Youngstown State University / Florida Atlantic University.
Report 52 Polymer Supported Chemical Reactions, P. Hodge, University of Manchester.
Report 53 Weathering of Polymers, S.M. Halliwell, Building Research Establishment.
Report 54 Health and Safety in the Rubber Industry, A.R. Nutt, Arnold Nutt & Co. and J. Wade.
Report 55 Computer Modelling of Polymer Processing, E. Andreassen, Å. Larsen and E.L. Hinrichsen, Senter for Industriforskning, Norway.
Report 56 Plastics in High Temperature Applications, J. Maxwell, Consultant.
Report 57 Joining of Plastics, K.W. Allen, City University. Report 58 Physical Testing of Rubber, R.P. Brown, Rapra
Report 59 Polyimides - Materials, Processing and Applications, A.J. Kirby, Du Pont (U.K.) Ltd.
Report 60 Physical Testing of Thermoplastics, S.W. Hawley, Rapra Technology Ltd.
Report 61 Food Contact Polymeric Materials, J.A. Sidwell, Rapra Technology Ltd.
Report 62 Coextrusion, D. Djordjevic, Klöckner ER-WE-PA GmbH. Report 63 Conductive Polymers II, R.H. Friend, University of
Report 66 Reinforced Thermoplastics - Composition, Processing and Applications, P.G. Kelleher, New Jersey Polymer Extension Center at Stevens Institute of Technology. Report 67 Plastics in Thermal and Acoustic Building Insulation,
V.L. Kefford, MRM Engineering Consultancy. Report 68 Cure Assessment by Physical and Chemical
Techniques, B.G. Willoughby, Rapra Technology Ltd. Report 69 Toxicity of Plastics and Rubber in Fire, P.J. Fardell, Building Research Establishment, Fire Research Station. Report 70 Acrylonitrile-Butadiene-Styrene Polymers,
M.E. Adams, D.J. Buckley, R.E. Colborn, W.P. England and D.N. Schissel, General Electric Corporate Research and Development Center.
Report 71 Rotational Moulding, R.J. Crawford, The Queen’s University of Belfast.
Report 72 Advances in Injection Moulding, C.A. Maier, Econology Ltd.
Report 73 Reactive Processing of Polymers, M.W.R. Brown, P.D. Coates and A.F. Johnson, IRC in Polymer Science and Technology, University of Bradford.
Report 74 Speciality Rubbers, J.A. Brydson.
Report 75 Plastics and the Environment, I. Boustead, Boustead Consulting Ltd.
Report 76 Polymeric Precursors for Ceramic Materials, R.C.P. Cubbon.
Report 77 Advances in Tyre Mechanics, R.A. Ridha, M. Theves, Goodyear Technical Center.
Report 78 PVC - Compounds, Processing and Applications, J.Leadbitter, J.A. Day, J.L. Ryan, Hydro Polymers Ltd. Report 79 Rubber Compounding Ingredients - Need, Theory
and Innovation, Part I: Vulcanising Systems, Antidegradants and Particulate Fillers for General Purpose Rubbers, C. Hepburn, University of Ulster. Report 80 Anti-Corrosion Polymers: PEEK, PEKK and Other
Polyaryls, G. Pritchard, Kingston University. Report 81 Thermoplastic Elastomers - Properties and
Applications, J.A. Brydson.
Report 82 Advances in Blow Moulding Process Optimization, Andres Garcia-Rejon,Industrial Materials Institute, National Research Council Canada.
Report 83 Molecular Weight Characterisation of Synthetic Polymers, S.R. Holding and E. Meehan, Rapra Technology Ltd. and Polymer Laboratories Ltd. Report 84 Rheology and its Role in Plastics Processing,
P. Prentice, The Nottingham Trent University.
Report 85 Ring Opening Polymerisation, N. Spassky, Université Pierre et Marie Curie.
Report 86 High Performance Engineering Plastics, D.J. Kemmish, Victrex Ltd.
Report 87 Rubber to Metal Bonding, B.G. Crowther, Rapra Technology Ltd.
Report 88 Plasticisers - Selection, Applications and Implications, A.S. Wilson.
Report 89 Polymer Membranes - Materials, Structures and
Report 92 Continuous Vulcanisation of Elastomer Proﬁles, A. Hill, Meteor Gummiwerke.
Report 93 Advances in Thermoforming, J.L. Throne, Sherwood Technologies Inc.
Report 94 Compressive Behaviour of Composites, C. Soutis, Imperial College of Science, Technology and Medicine. Report 95 Thermal Analysis of Polymers, M. P. Sepe, Dickten &
Masch Manufacturing Co.
Report 96 Polymeric Seals and Sealing Technology, J.A. Hickman, St Clair (Polymers) Ltd.
Report 97 Rubber Compounding Ingredients - Need, Theory and Innovation, Part II: Processing, Bonding, Fire Retardants, C. Hepburn, University of Ulster. Report 98 Advances in Biodegradable Polymers, G.F. Moore &
S.M. Saunders, Rapra Technology Ltd.
Report 99 Recycling of Rubber, H.J. Manuel and W. Dierkes, Vredestein Rubber Recycling B.V.
Report 100 Photoinitiated Polymerisation - Theory and Applications, J.P. Fouassier, Ecole Nationale Supérieure de Chimie, Mulhouse.
Report 101 Solvent-Free Adhesives, T.E. Rolando, H.B. Fuller Company.
Report 102 Plastics in Pressure Pipes, T. Stafford, Rapra Technology Ltd.
Report 103 Gas Assisted Moulding, T.C. Pearson, Gas Injection Ltd. Report 104 Plastics Proﬁle Extrusion, R.J. Kent, Tangram
Report 105 Rubber Extrusion Theory and Development, B.G. Crowther.
Report 106 Properties and Applications of Elastomeric Polysulﬁdes, T.C.P. Lee, Oxford Brookes University. Report 107 High Performance Polymer Fibres, P.R. Lewis,
The Open University.
Report 108 Chemical Characterisation of Polyurethanes, M.J. Forrest, Rapra Technology Ltd.
Report 109 Rubber Injection Moulding - A Practical Guide, J.A. Lindsay.
Report 110 Long-Term and Accelerated Ageing Tests on Rubbers, R.P. Brown, M.J. Forrest and G. Soulagnet,
Rapra Technology Ltd.
Report 111 Polymer Product Failure, P.R. Lewis, The Open University.
Report 112 Polystyrene - Synthesis, Production and Applications, J.R. Wünsch, BASF AG.
Report 113 Rubber-Modiﬁed Thermoplastics, H. Keskkula, University of Texas at Austin.
Report 114 Developments in Polyacetylene - Nanopolyacetylene, V.M. Kobryanskii, Russian Academy of Sciences. Report 115 Metallocene-Catalysed Polymerisation, W. Kaminsky,
University of Hamburg.
Report 116 Compounding in Co-rotating Twin-Screw Extruders, Y. Wang, Tunghai University.
J.A. Sidwell, Rapra Technology Ltd.
Report 120 Electronics Applications of Polymers II, M.T. Goosey, Shipley Ronal.
Report 121 Polyamides as Engineering Thermoplastic Materials, I.B. Page, BIP Ltd.
Report 122 Flexible Packaging - Adhesives, Coatings and Processes, T.E. Rolando, H.B. Fuller Company. Report 123 Polymer Blends, L.A. Utracki, National Research
Report 124 Sorting of Waste Plastics for Recycling, R.D. Pascoe, University of Exeter.
Report 125 Structural Studies of Polymers by Solution NMR, H.N. Cheng, Hercules Incorporated.
Report 126 Composites for Automotive Applications, C.D. Rudd, University of Nottingham.
Report 127 Polymers in Medical Applications, B.J. Lambert and F.-W. Tang, Guidant Corp., and W.J. Rogers, Consultant. Report 128 Solid State NMR of Polymers, P.A. Mirau,
Report 129 Failure of Polymer Products Due to Photo-oxidation, D.C. Wright.
Report 130 Failure of Polymer Products Due to Chemical Attack, D.C. Wright.
Report 131 Failure of Polymer Products Due to Thermo-oxidation, D.C. Wright.
Report 132 Stabilisers for Polyoleﬁns, C. Kröhnke and F. Werner, Clariant Huningue SA.
Report 133 Advances in Automation for Plastics Injection Moulding, J. Mallon, Yushin Inc.
Report 134 Infrared and Raman Spectroscopy of Polymers, J.L. Koenig, Case Western Reserve University. Report 135 Polymers in Sport and Leisure, R.P. Brown. Report 136 Radiation Curing, R.S. Davidson, DavRad Services. Report 137 Silicone Elastomers, P. Jerschow, Wacker-Chemie GmbH. Report 138 Health and Safety in the Rubber Industry, N. Chaiear,
Khon Kaen University.
Report 139 Rubber Analysis - Polymers, Compounds and Products, M.J. Forrest, Rapra Technology Ltd. Report 140 Tyre Compounding for Improved Performance,
M.S. Evans, Kumho European Technical Centre. Report 141 Particulate Fillers for Polymers, Professor R.N. Rothon,
Rothon Consultants and Manchester Metropolitan University.
Report 142 Blowing Agents for Polyurethane Foams, S.N. Singh, Huntsman Polyurethanes.
Report 143 Adhesion and Bonding to Polyoleﬁns, D.M. Brewis and I. Mathieson, Institute of Surface Science & Technology, Loughborough University.
Report 146 In-Mould Decoration of Plastics, J.C. Love and V. Goodship, The University of Warwick. Report 147 Rubber Product Failure, Roger P. Brown. Report 148 Plastics Waste – Feedstock Recycling, Chemical
Recycling and Incineration, A. Tukker, TNO.
Report 149 Analysis of Plastics, Martin J. Forrest, Rapra Technology Ltd.
Report 150 Mould Sticking, Fouling and Cleaning, D.E. Packham, Materials Research Centre, University of Bath. Report 151 Rigid Plastics Packaging - Materials, Processes and
Applications, F. Hannay, Nampak Group Research & Development.
Report 152 Natural and Wood Fibre Reinforcement in Polymers, A.K. Bledzki, V.E. Sperber and O. Faruk, University of Kassel.
Report 153 Polymers in Telecommunication Devices, G.H. Cross, University of Durham.
Report 154 Polymers in Building and Construction, S.M. Halliwell, BRE.
Report 155 Styrenic Copolymers, Andreas Chrisochoou and Daniel Dufour, Bayer AG.
Report 156 Life Cycle Assessment and Environmental Impact of Polymeric Products, T.J. O’Neill, Polymeron Consultancy Network.
Report 157 Developments in Colorants for Plastics, Ian N. Christensen.
Report 158 Geosynthetics, David I. Cook.
Report 159 Biopolymers, R.M. Johnson, L.Y. Mwaikambo and N. Tucker, Warwick Manufacturing Group.
Report 160 Emulsion Polymerisation and Applications of Latex, Christopher D. Anderson and Eric S. Daniels, Emulsion Polymers Institute.
Report 161 Emissions from Plastics, C. Henneuse-Boxus and T. Pacary, Certech.
Report 162 Analysis of Thermoset Materials, Precursors and Products, Martin J. Forrest, Rapra Technology Ltd. Report 163 Polymer/Layered Silicate Nanocomposites, Masami
Okamoto, Toyota Technological Institute.
Report 164 Cure Monitoring for Composites and Adhesives, David R. Mulligan, NPL.
Report 165 Polymer Enhancement of Technical Textiles, Roy W. Buckley.
Report 166 Developments in Thermoplastic Elastomers, K.E. Kear
Report 167 Polyoleﬁn Foams, N.J. Mills, Metallurgy and Materials, University of Birmingham.
Report 168 Plastic Flame Retardants: Technology and Current Developments, J. Innes and A. Innes, Flame Retardants Associates Inc.
Report 169 Engineering and Structural Adhesives, David J. Dunn, FLD Enterprises Inc.
Report 170 Polymers in Agriculture and Horticulture, Roger P. Brown.
Report 171 PVC Compounds and Processing, Stuart Patrick. Report 172 Troubleshooting Injection Moulding, Vanessa
Report 174 Pharmaceutical Applications of Polymers for Drug Delivery, David Jones, Queen's University, Belfast. Report 175 Tyre Recycling, Valerie L. Shulman, European Tyre
Recycling Association (ETRA).
Report 176 Polymer Processing with Supercritical Fluids, V. Goodship and E.O. Ogur.
Report 177 Bonding Elastomers: A Review of Adhesives & Processes, G. Polaski, J. Means, B. Stull, P. Warren, K. Allen, D. Mowrey and B. Carney.
Report 178 Mixing of Vulcanisable Rubbers and Thermoplastic Elastomers, P.R. Wood.
Report 179 Polymers in Asphalt, H.L. Robinson, Tarmac Ltd, UK. Report 180 Biocides in Plastics, D. Nichols, Thor Overseas Limited.
Report 181 New EU Regulation of Chemicals: REACH, D.J. Knight, SafePharm Laboratories Ltd.
Report 182 Food Contact Rubbers 2 - Products, Migration and Regulation, M.J. Forrest.
Report 183 Adhesion to Fluoropolymers, D.M. Brewis and R.H. Dahm, IPTME, Loughborough University.
Report 184 Fluoroplastics, J.G. Drobny.
Report 185 Epoxy Composites: Impact Resistance and Flame Retardancy, Debdatta Ratna.
Report 186 Coatings and Inks for Food Contact Materials, Martin Forrest, Smithers Rapra.
Report 187 Nucleating Agents, Stuart Fairgrieve, SPF Polymer Consultants.
Report 188 Silicone Products for Food Contact Applications, Martin Forrest, Smithers Rapra.
Report 189 Degradation and Stabilisation of Polymers, Stuart Fairgrieve, SPF Polymer Consultants Report 190 Electrospinning
Jon Stanger, New Zealand Institute for Plant and Food Research
Nick Tucker, New Zealand Institute for Plant and Food Research
Processing and Applications
Viscosity in Solution ...7
PVAL Film Properties ...9
6.1 Barrier Proporties ...9
6.2 Other Film Properties ...10
Oil and Solvent Resistance ...10
Water Sensitivity and Hygroscopy ...10
10. PVAL in Medicine: Hydrogels ...13
13. Blends of PVAL ...15
The views and opinions expressed by authors in Rapra Review Reports do not necessarily reﬂect those
of Smithers Rapra Technology or the editor. The series is published on the basis that no responsibility
or liability of any nature shall attach to Smithers Rapra Technology arising out of or in connection with
any utilisation in any form of any material contained therein.
Author contact details: Vannessa Goodship
WMG, Univeristy of Warwick, Coventry, CV4 7AL
WMG, Univeristy of Warwick, Coventry, CV4 7AL
14.2 Oil-Based Naturally Degradable Polymers ...18
15. Plastics and Biodegradable Plastics Disposal ...19
Abbreviations and Acronyms ...22
Subject Index ...00
Properties, Applications and Disposal
This review report is produced to provide a concise introduction to poly(vinyl alcohol); the material itself, processing, applications and disposal. It will also consider comparable properties of similar materials with which this material is likely to compete. The deﬁnitions and requirements of materials that wish to operate in the ‘green’ arena will also be introduced.
Poly(vinyl alcohol) is the most commercially important water soluble plastic in use. It is tasteless, odourless, it will biodegrade and is biocompatible. As well as being soluble in water, it is slightly soluble in ethanol, but insoluble in other organic solvents. As environmental concerns over the disposal of plastic wastes have grown and focus has switched towards product life cycle and disposal, poly(vinyl alcohol) has a readymade and viable disposal route. In light of increasing environmental legislation, this will allow it to be utilised in non-traditional areas of use. With increasing interest in the use of biodegradable and sustainable alternatives for mass applications, poly(vinyl alcohol) provides an interesting point of comparative study on a oil-based synthetic material with the properties of a ‘green polymer’.
It is also be readily blended with a number of natural materials and can exhibit properties that are compatible with a range of applications. The inclusion of natural ﬁbres and ﬁllers can give further improvements in mechanical properties without compromising overall degradability. Therefore, the potential beneﬁts of this material given its water soluble characteristics are huge, but this must be offset against practical considerations of its long term life cycle in changeable environmental conditions.
In the future biodegradable materials could be used within a variety of product applications, but there are, at present, signiﬁcant penalties in terms of performance, cost and availability. The predominant beneﬁt which can be attributed to biopolymer usage is that the materials themselves can be biodegradable. This of course makes them an increasingly attractive proposition for manufacturers who are faced with increasingly stringent EU legislative requirements when it comes to the environmental performance of their products, or those who wish to tap the market of the environmentally conscious consumer. This review will try to capture current and future trends in this area.
Like all common polymers poly(vinyl alcohol) can be abbreviated. However, unlike polymers such as polypropylene (PP), in which the abbreviations are universally used, poly(vinyl alcohol) does not have a singularly recognised abbreviation. Therefore according to various literature sources it is referred to as PVAL, PVOH or PVA and therefore all these terms, although confusing, are correct in the context of the standards to which they were used.
The terminology that shall be used here is PVAL in accordance to British Standard BS EN ISO 15023-1:2006 (a.1).
Poly(vinyl alcohol) and its properties have been known to scientists for a long time. It was ﬁrst prepared by Hermann and Haehnel, Germany, in 1924. It is made by hydrolysing polyvinyl acetate (PVA or PVAc – dependent on where you look).
Worldwide consumption of PVAL had reached several hundred thousand tonnes annually in 2006; this is widely predicted to increase by about 2.5% annually between 2006 and 2011. There are a number of worldwide producers of this material with the majority of production based in Asian countries. China has the largest share of the market as of commercial trading ﬁgures for 2006 with 45% of the entire market with this ﬁgure likely to expand. Japan and the United States are also both large producers and consumers of PVAL materials. Kuraray (Japan) is the largest single manufacturer of PVAL accounting for 16% of all world capacity and offering over 50 different grades of this material.
Trade names for PVAL (PVOH or PVA) include Elvanol (DuPont), Mowiol (Kuraray) and Poval (Kuraray).
The material exists in the marketplace as fully hydrolysed, medium hydrolysed or partially hydrolysed copolymers or custom blends. Most of the market is dominated by sales of the fully hydrolysed grade of material. This difference in hydrolysis will be explained in Section 4. In line with international standards, grades of this material are presented in terms of the degree of hydrolysis and the viscosity in water at speciﬁed conditions. An indication of the range of hydrolysis levels available in the marketplace is shown in Table 1.
Using 2008 commercial prices as a general guide, PVAL materials are priced according to viscosity. Low viscosity materials (classed as having a viscosity less than 0.01 Pa-s), were trading for half the price per tonne (150 Euros), than high viscosity materials (>0.03 Pa-s) which were trading at 300 Euros per tonne. Medium viscosity materials (0.01-0.03 Pa-s) were trading at 200 Euros. However, like all oil-based plastics prices are highly variable.
2. Application Scope
The major uses of PVAL depend on region. In the United States and Western Europe the majority of PVAL is consumed in the production of poly(vinyl butyral) (PVB). This is used in the inner layer of laminated safety glass for automobile window screens. It is made by reacting PVAL with butyraldehyde [CH3(CH2)2CHO] and this market is one which is
expected to grow in the future.
PVAL ﬁnds other uses in a broad range of products produced for example as a protective colloid in the manufacture of polymer emulsions. Other applications include: the binding of pigments and fibres, dip coated articles, protective strippable coatings, the manufacture of detergents and cleansing agents, adhesives, emulsion paints, and solution cast ﬁlm. These applications all involve the use of the PVAL in solution as its thermal degradation at about 150 °C (crystalline melting point of PVAL ranges from 180 °C to 240 °C), limits its ability to be used in conventional thermoplastic processing equipment without modiﬁcation. When PVAL is plasticised, it
is possible to avoid thermal dehydration however, some properties are sacriﬁced.
In China the largest market is as a polymerisation aid in emulsiﬁed polyvinyl acetate and polyvinyl chloride (PVC). Therefore, much of the PVAL produced today is used as a protective colloid in the manufacture of polymer emulsions.
The use of emulsifying agents improves the quality of synthesis of PVC and helps properties such as the ability to absorb plasticisers and the production of uniform grain sizes. Other materials commonly used as emulsifying agents are methyl cellulose derivatives or combinations. Two PVAL materials of differing molecular weight may be used together synergistically improving the process.
In the formation of emulsified polyvinyl acetate, PVAL acts as a protective colloid. PVAL has excellent properties in emulsion such as ‘wet tackiness’, high strength and it is highly resistant to creep. As with the formation of PVC, the structure of the PVAL affects the emulsion performance of the polyvinyl acetate. For this process, PVAL with an active surface is also required, therefore partially hydrolysed grades are utilised which have residual acetate groups which are hydrophobic in nature.
In Japan Vinylon spun ﬁbre is the biggest use of PVAL. It is used in a variety of applications from the manufacture of traditional Japanese dress, canvas, cement reinforcement, agriculture, ﬁshing nets, ropes and paper making (which is the largest market). It can be produced by either dry or wet spinning. This is a different process to spinning from a melt, which is called melt spinning and used for production of ﬁbres
Table 1 Selection of grades of PVAL offered by Kuraray
DIN 53015 (a.2) (mPa-s)*
Degree of hydrolysis (saponiﬁcation) (mol. - %)
Partially hydrolysed Mowiol 3-85 3.4-4.0 84.2-86.2
Partially hydrolysed PVA 220 27.0-33.0 87.0-89.0
Partially hydrolysed PVA 225 45.0-52.0 86.5-89.0
Medium Hydrolysed PVA CST 24.0-30.0 95.5-96.5
Medium Hydrolysed PVA 613 14.5-18.5 92.5-94.5
Fully hydrolysed PVA 117 25.0-30.0 98.0-99.0
Fully hydrolysed Mowiol 4-98 4.0-5.0 98.0-98.8
Fully hydrolysed Mowiol 56-98 52.0-60.0 98.0-98.8
such as polyethylene (PE), PP, polyamide (PA) and polyester. In the case of vinylon a spinning solution is used with most production then carried out by wet spinning. The product is staple ﬁbre. The solution is spun into ﬁbres which pass through a water bath before being drawn and cut into ﬁbres. Dry spinning uses hot air instead of water, drawing and then collection of the ﬁlament yarn onto spindles. Vinylon is characterised by a lighter weight (speciﬁc gravity of 1.3) than natural ﬁbres such as wool or cotton. It is abrasion resistant, durable and resistance to weathering, chemicals and rotting and has properties similar to cotton in ﬁbre form.
Demand is also increasing for PVAL fibres as a safer replacement for asbestos ﬁbres and in the use of polarising optical ﬁlms for liquid crystal displays (LCD) (a.3). The PVAL material is used for optical applications which effectively prevent reﬂection of light at the surface of image display devices such as plasma display panels (PDP), cathode ray tubes (CRT) and LCD, and exhibits excellent scratch resistance. The ﬁlm, used for preventing reﬂection of light has excellent scratch resistance and can be produced at a low cost. In a typical application, the ﬁlm is formed by successively laminating a hard coat layer, a ﬁrst high refractivity layer, a second high refractivity layer, and a low refractivity layer.
The water solubility and biodegradability of this material are the key properties for its usage. This has also attracted the recent attention of a packaging industry keen to address environmentally friendly solutions to the issue of plastic waste. This will be discussed in Section 5.
Other important areas where PVAL water solubility is used include textile sizing agents – the PVAL is applied to protect the textile ﬁbres during production (such as knitting or weaving and so on), then once made the garment can be washed to remove the PVAL.
PVAL adhesives are used widely with cellulose materials as they give excellent adhesion to them. They are, therefore, used in a range of applications from postage stamps, labels, paper bags to book binding and make an ideal glue for papercraft activities.
Commercially, PVAL is the most important plastic for production of water soluble ﬁlm. It is characterised by excellent ﬁlm-forming, emulsifying, and adhesive properties. It has a high tensile strength, good ﬂexibility, good oxygen barrier properties and good solvent resistance properties.
All the applications so far involve the use of the PVAL in solution as its thermal degradation is about 150 °C (crystalline melting point of PVAL ranges from 180 °C to 240 °C). Therefore until recently this limited its ability to be used in conventional thermoplastic processing equipment. However, when PVAL is plasticised, it is possible to avoid thermal dehydration. Melt processing applications are discussed in Section 8.
Therefore, PVAL ﬁnds use in variety of market sectors such as (a.3): s s s s s s s s
PVAL was investigated in the 1970s for use in controlled release of agrochemicals using combinations with pesticides. It is also used in current production of seed tapes. For these kind of applications the polymer must degrade without impact (be it chemical or biological) to the surrounding environment. Therefore, degradation and disposal issues will also be discussed later in the review.
PVAL is used in the manufacture of laundry bags and hamper liners for use in health care facilities. The ﬁlled bag is sealed shut with an attached adhesive strip. When placed in the washer, the adhesive and bag break down completely during the hot washing and disinfection. The bags are impervious to bacteria and viruses during normal use, as well as resistant to gases, solvents, and cool liquids, reducing the risk of contamination and thereby protecting hospital staff.
In food industries, PVAL is used as a binding and coating agent. The ﬁlm coating is used in applications where moisture barrier protection properties are required. PVAL protects active components and other ingredients from oxygen, e.g., tablet coating formulations intended for products such as food supplement tablets.
Other more unusual products include the biodegradable PVAL pet waste bag for picking up pet waste and eco-disposal. It can be placed in the bin or ﬂushed down the toilet. For lazy (or inept) golfers, there are water soluble golf balls made from PVAL. For golfers not willing to look for their balls, these can be abandoned on courses
Figure 1 Molecule of PVAL (left) and chemical representations (right and centre) to biodegrade naturally. For those who wish to practise
their swings while at sea, they can be hit straight into the sea to dissolve.
This variety of sectors and applications areas are possible because poly(vinyl alcohol) has a number of useful and tailorable properties. It is odourless and non-toxic, it has excellent ﬁlm forming, emulsifying, and adhesive properties. It also has good resistance to grease, oils and a large number of solvent materials. It has good mechanical performance with high tensile strength and ﬂexibility, it also has high oxygen and aroma barrier properties. However, these properties are all dependent on the level of humidity. Water, which acts as a plasticiser, causes a reduction in tensile strength, but also increases the elongation and tear strength of the material.
The sheer range of applications for this material make it an interesting material of study. However, ﬁrst a more fundamental introduction to PVAL manufacture and material properties will be given.
The ﬁrst commercial production of PVAL was by the company Wacker (Germany) with the trademark Synthoﬁl, which was used as medical sutures. In 1930, Japanese researchers Sakurada, Yazawa and Tomanari successfully wet spun PVAL. In 1950 this was realised commercially as Vinylon fibre (see Section 2). This ﬁbre has high heat resistance amongst other interesting properties.
Unlike other members of the vinyl group, PVAL is not polymerised from a monomer in direct polymerisation, but prepared by hydrolysis of poly(vinyl acetate) (PVAc) in alcohol solution. This is a rubbery, synthetic polymer and partial or complete hydrolysis of the PVAc is used to prepare PVAL. The reaction proceeds via free radical mechanism or suspension polymerisation. Partial or complete hydrolysis removes acetate groups from the PVAc. The resultant material PVAL has the same degree of polymerisation as the original PVAc material. Therefore by varying the degree of polymerisation of the original PVAc a number of different grades of material with different properties can be produced. The reaction can be controlled to produce any degree of replacement of acetate groups. Other materials can be used to produce co-polymer materials which also replace the acetate group. Monomers such as ethylene and acrylate esters are commercially used in this way.
Once converted from PVAc the hydrolysed alcohol product is typically in the 87% to 99% range. If it is above 98% it can be considered to be fully hydrolysed with an expected crystallinity value of 40-50% Highly but not fully hydrolysed PVAL has a degree of crystallinity of 30-40% and a melting point of 225 °C. The reduced crystallinty in partially hydrolysed grades is due to the residual acetate groups. Other factors affecting crystallinity are the amount of plasticiser and water present in the compound. The production process used (acid or base catalysed) also has an effect. A lower crystallinity means lower strength but increased water solubility compared to fully hydrolysed (higher crystallinity) grades which can be considered as homopolymers as opposed to mixed vinyl acetate and vinyl alcohol co- polymer. Chemical representations commonly used to represent PVAL are shown in Figure 1.
4. Polymer Chemistry
The physical characteristics and speciﬁc functional uses depend on the both the degree of polymerisation and hydrolysis produced. PVAL is classiﬁed into classes namely: partially hydrolysed and fully hydrolysed. PVAL is crystalline in nature, this is unusual since it is an atactic linear polymer, meaning the positioning of the side chains of secondary alcohol groups is random. This is generally accompanied by an inability to crystallise. In fact PVAc is not crystalline, but PVAL which contains smaller hydroxyl groups, is typically crystalline regardless of stereoregularity. This is because hydroxyl groups do not disrupt the crystalline lattice structure as their small size allows them to ‘slot’ in. However, in contrast, the presence of residual acetate groups greatly diminishes the crystal formation and the degree of hydrogen bonding because of their more bulky nature.
Therefore, polymers that are highly hydrolysed have a high tendency to crystallise and to undergo hydrogen bonding. As the degree of hydrolysis increases, the molecules will very readily crystallise, and hydrogen bonds will keep them associated if they are not fully dispersed prior to dissolution. At degrees of hydrolysis above 98%, manufacturers of PVAL advocate a minimum temperature of 96 °C to ensure that the highest molecular weight components have enough thermal energy to go into solution.
Increasing levels of hydrolysis leads to increasing
This also allows a level of control to be exerted over the crystallinity produced and the physical characteristics and speciﬁc functional uses of PVAL vary with this property. The crystallinity affects the water solubility, strength, gas permeability and thermal characteristics. Since the crystallinity is dependent on both the degree of hydrolysis and the average molecular weight of the polymer it also depends on the degree of polymerisation that occurs.
The level of hydrolysis will therefore have a direct effect on the properties and it is necessary to distinguish these materials into levels (partially, medium, fully hydrolysed). The actual degree of hydrolysis depends on how many percentage mol of residual acetate groups remain, as PVAL is characterised by the presence of the polar OH groups in the structure. For ISO 15023 (a.1), the level must be equal to or above 70%.
Because PVAL refers to the material that can be both fully and partly hydrolysed, it can actually be considered in partially hydrolysed cases to be a co-polymer of vinyl acetate and vinyl alcohol monomer (which does not actually exist). The monomer components may be distinguished if necessary using the convention V-AL and V-OAc.
Therefore PVAL is characterised by the presence of polar alcohol (OH-groups), and these groups give rise to reduced water solubility and also allow other reactions to take place.
Increasing hydrolysis leads to: s s s
In many cases, however, a partially or fully hydrolysed material may be used for the same application. For example in adhesives, where water resistance is required, a fully hydrolysed material may be used and where water resistance is not an issue, a partially or fully hydrolysed material may be used.
It is a water-soluble synthetic polymer that is it is made from petrochemicals. So although it is biodegradable, it is not a biopolymer. A biopolymer is a material made from a biomaterial such as plant starch. This distinction will be discussed in Section 10.
4.1 Viscosity in Solution
In water solution partially hydrolysed PVAL (88% and below) has a stable viscosity which does not change over time. However, the viscosity of a solution of highly hydrolysed material will show a gradual increase in viscosity over time, and if left long enough may even gel. This tendency to increase in viscosity over time, increases fairly linearly with concentration.
The ﬁlms produced from partially hydrolysed solutions are characterised with poor water and heat resistance. Those from fully hydrolysed grades have the opposite properties being water and creep resistant properties. Through the use of additives it is possible to stabilise or destabilise those changes in viscosity which occur.
5. Water Solubility
The main use of PVAL is when it is dissolved in water. Poly(vinyl alcohol) is among a group of water-soluble plastics that have a long history of use in niche applications. Many of these polymers are biologically stable when they are in the solid state but will biodegrade readily once they are dissolved. As PVAL is formed by hydrolysis of PVAc, by controlling the degree of hydrolysis, its solubility can be modiﬁed, which results in grades that will dissolve only in hot or cold water. Some grades can be mass produced by extrusion, injection moulding or ﬁlm blowing (to produce potentially readily disposable components), but others must be cast from solution.
Single dose laundry blocks or liquids have become commonplace in many households. These are water soluble ﬁlms used for the packaging (as you will ﬁnd if you accidentally get them wet, they become very sticky.) Surprisingly the first use of water soluble packaging was in the 1960s, this was for carrying harmful chemicals in agriculture. It is relatively more recently that they have become such a commonplace item for household detergents and cleaning items. As already mentioned, the solubility depends on a number of factors such as the degree of polymerisation and degree of hydrolysis. The degree of hydrolysis is particularly important because of the inherent chemical structure. The many hydroxyl groups mean it has a high afﬁnity for water and the hydrogen bonding between the hydroxyl groups impedes the overall solubility. In contrast, partly hydrolysed PVAL contains acetate groups. This acts in the opposite way to weaken the hydrogen bonding and increase solubility and there is a relationship between temperature of solubility and presence of acetate groups. Therefore, the behaviour of PVAL in solution is quite complex.
However, generally a partially hydrolysed version of the same material will be more soluble at a lower temperature with solubility increasing as hydrolysis levels increase.
Commercial water-soluble ﬁlms can be tailored to dissolve in water at very speciﬁc temperatures. PVAL is not the only water soluble polymer on the market. Other water soluble polymers are shown in Table 2.
Table 2 Water-soluble polymers
Type Production Source
PVAL Synthetic* Non-renewable*
Ethylene vinyl alcohol (EVOH) Synthetic* Non-renewable* Cellulose acetate Natural Renewable (cellulose)
Chitosan Natural Renewable
(invertebrates) * made from fossil fuels
The term non-renewable source refers to the use of fossil fuels, which are ﬁnite in nature. PVAL and EVOH are highly unusual, synthetic crude oil-based polymers in that they dissolve in water. EVOH is most commonly used as an oxygen barrier layer in multi-layer film packaging (see Section 7.1) although it is expensive to use and the high price limits its applications elsewhere. PVAL is also the only polymer consisting of a carbon-carbon backbone that biodegrades. Polymers made from renewable resources include plant-based materials such as plant starch (which can be renewed by re-planting crops) and animals sources such as chitosan (found in insect exo-skeletons). Chitosan also has good gas barrier properties and is used as a coating for other biodegradable polymers and edible coatings. Both cellulose acetate and chitosan are water-soluble. The water solubility of polymer materials means that they can end up as pollutants in water ecosystems (river, ocean) and affect aquatic life if they are not monitored and removed. Removal is done by microorgasms for PVAL and other similar potentially water soluable pollutants include polyacylics, polycarboxylates, polyethers and polyglutamic. For PVAL, research as far back as 1936 (a.6) found that PVAL in waste water was biodegraded by a phytopathogenic organism of fungal origin, Fusarium lini. The by-products being water and carbon dioxide. Since then many studies have been carried out on PVAL degradation in both aerobic conditions and soil samples with satisfactory results. The actual biodegradation mechanisms are beyond the scope of this review however the reader is referred to a survey carried out by Chiellini and co-workers (a.7) in 2003 for an overview of this subject.
The solubility of PVAL makes a big difference to the ﬁnal application. For example consider three alternative PVAL materials that can be considered as very soluble, moderately soluble and slightly
soluble. A guide to potential applications based on this property is shown in Table 3.
Table 3 Solubility as application guide
Very soluble Moderately
soluble Slightly soluble Pharmaceutical capsules which dissolve to release drugs Loose ﬁll packaging Food packaging
Medical sutures Agricultural ﬁlms
Diaper ﬁlms Detergent single
Single use food service items
Medical containers Life span short Life span:
Life span: high – must survive until disposal
As we have seen, the solubility of PVAL depends on both the molecular weight and the level of hydrolysis. To add to this, PVAL that is partly hydrolysed is less dependent on temperature to be soluble. For highly hydrolysed grades however, it may be necessary for solutions to reach temperatures just under 100 °C before dissolution occurs. For disposal of items such as food packaging, diaper ﬁlms and medical containers, left to degrade in the environment, it is unlikely that they would ever reach high enough temperatures to dissolve in rain water for example. It is therefore, necessary to consider whether degradation by environmental conditions or degradation by dissolving into water is the required outcome. Methods of degradation will be covered later in Section 14.
Partially hydrolysed PVAL is easier to dissolve than fully hydrolysed PVAL
6. PVAL Film Properties
PVAL is the most commercially important water soluble film, therefore, it is worth taking a look at the major properties of these materials.
Given their water soluble nature it is probably not surprising that the first consideration is that the resultant mechanical properties depend on humidity. High humidity produces a film which is soft and tough. Low humidity gives a hard and brittle material. These depend initially on the degree of polymerisation since tensile strength and elongation increase with degree of polymerisation
and partly hydrolysed materials are weaker than fully hydrolysed materials.
A higher degree of polymerisation gives increasing strength, but humidity has the effect of a plasticiser,
swelling the structure to make it softer and tough.
6.1 Barrier Proporties
PVAL materials have excellent oxygen barrier properties (and also act as a barrier to carbon dioxide and nitrogen). These values are comparable to the performance of EVOH and much better than the common commodity packaging materials listed in Table 4.
Table 4 Oxygen permeability of
common materials and PVAL
(30 μm ﬁlm, 50% humidity)
Material Oxygen Permeability
Hot water soluble PVOH 0.24
Warm water soluble PVOH 0.36
Cold water soluble PVOH 1.85
EVOH 0.29-2.4 Nylon 6 26-38 PET 40-80 PVC 50-390 High-density polyethylene (HDPE) 1700-2400 PP 2,000-10,000 Low-density polyethylene (LDPE) 12,000
An increase in dissolution temperature (and crystallinity) improves the performance of the oxygen barrier. However, the downside is the afﬁnity to water. Water vapour will permeate through the ﬁlms and therefore PVAL is a poor barrier to water vapour. Interestingly this is the opposite of polyethylene which allows oxygen to pass through its structure but not water vapour. Wet PVAL ﬁlm has little strength but a dry ﬁlm has good tensile properties.
PVAL has found application as a barrier layer in ﬂexible packaging but not in rigid packaging (such as bottles) where EVOH and PA are utilised. Whilst aluminium of micrometer thickness is traditionally used in ﬂexible packaging, creating a virtually perfect barrier, using plastics by lamination or co-extrusion gives high (but not perfect) barrier performance but at a better cost
performance. Other ﬂexible packaging barrier materials used in this way include poly(vinylidene chloride) (PVDC), EVOH or PA.
However, it needs to be considered that PVAL, EVOH and PA are only effective barriers in a dry state. Therefore, sandwich constructions in which they are protected by materials with water barrier properties are necessary to maintain the oxygen barrier properties of these materials.
6.2 Other Film Properties
6.2.1 Mechanical Properties
Degree of polymerisation affects both the tensile strength and elongation ﬁlm properties, so that as the degree of polymerisation increases so does the strength. The tensile strength also increases with a rise in the degree of hydrolysis.
However, as well as these factors, the humidity also has a marked effect on physical properties.
At low humidities, PVAL ﬁlm is hard and brittle, whilst at high humidity it is soft and ﬂexible due to the plasticising effect of the water vapour. This dependence is greater for partially hydrolysed grades than for those that are fully hydrolysed.
Humidity leads to increased ﬂexibility and softness.
6.2.2 Plasticiser Effects
Water acts as a plasticiser for PVAL whether by the action of humidity or as a solution. At low humidities the same effect can be achieved by glycols which serve to prevent the PVAL ﬁlm from becoming hard and brittle. For thermal processing techniques such as injection moulding it is necessary to add plasticiser to prevent premature degradation. These will be discussed further in the thermal processing section.
6.2.3 Oil and Solvent Resistance
PVAL is highly resistant to oils (animal, vegetable or mineral origin) and organic solvents (aromatic and aliphatic hydrocarbons, esters, ethers and ketones). This resistance like many of the other properties of PVAL is
affected by the degree of polymerisation and the degree of hydrolysis.
6.2.4 Water Sensitivity and Hygroscopy
PVAL ﬁlms will swell and take up water if immersed. Partially hydrolysed grades have higher levels of hygroscopy and solubility to water vapour than fully hydrolysed grades.
These factors and the rate of swelling can all be decreased by heat treatment which increases the crystallinity of the ﬁlm.
6.2.5 Adhesion Characteristics
As the degree of hydrolysis increases there is a change in the relative number of acetate and hydroxyl groups present. This in turn creates changes in the adhesion character of the ﬁlm.
When used as an adhesive agent, low degrees of hydrolysis give adhesion to hydrophobic surfaces, higher degrees of hydrolysis lead to adhesion to hydrophilic (strong afﬁnity for water) surfaces.
PVAL is resistant to static build up and this property can be useful in packaging applications where atmospheric dust is present.
7. Solution Processing
The spinning of Vinylon ﬁbres from solution, primarily of interest only to the Japanese market has already been discussed. Another process using PVAL in solution to spin ﬁbres is electrospinning. In this case very thin, nano-sized ﬁbres can be produced, allowing the resultant ﬁbres to be used in a range of medical and ﬁltration applications. The major drawback with electrospinning is the volumes that can be produced. If large volume equipment comes onto the market, this type of manufacture could be applicable to more than just niche markets.
Since many applications described here are carried out in solution, it is worth considering how these
solutions are made. These methods can also be used to differentiate between a fully hydrolysed and partially hydrolysed grade.
It has been shown that the solubility is dependent on two factors, degree of polymerisation and hydrolysis. Fully hydrolysed grades are not really soluble at room temperature so a stirred water/PVAL mixture will need to be heated to nearly boiling to ensure full dissolution.
For partially hydrolysed grades, the plasticiser effect of the water and solubility means the solute (PVAL in this case) tends to form lumps if prepared in the same way as fully hydrolysed grades, therefore in this case, the PVAL should be added slowly to the solution whilst stirring. The temperature can be raised if necessary to speed this process up.
Whilst solution concentrations obviously vary from application to application, a 10% solution is a very common dilution rate for PVAL and can therefore be considered as an indicator of the levels of PVAL used in solution for the purposes here.
8. Melt Processing
PVAL has a decomposition temperature of 180 °C. However it does not melt below 180 °C, and has a melting point range of between 180 and 240 °C. Some properties are shown in Table 5. Therefore thermal processing of PVAL presented a considerable challenge worldwide.
Table 5 Properties of PVAL
Property Typical value
Density 1.19-1.31 g/cm³
Melting point 180-240 °C (dependent
on degree of hydrolysis)
Boiling point 228 °C
Degradation temperature (unplasticised)
Unplasticised PVAL degrades at temperatures above 180 °C due to water elimination from the chemical structure. Further degradation can cause discoloration and crosslinking to occur as the hydroxyl and acetate side groups are eliminated. Whilst the melting point of PVAL can vary between 180-240 °C depending on the level of hydrolysis, the effect of the relatively
low degradation reaction temperature means that melt processing applications a limited to only materials with low hydrolysis levels or materials that a heavily plasticised (which generally meant sacriﬁcing the useful properties inherent in the PVAL materials in the ﬁrst place).
Therefore, until the last decade, the unwelcome onset of thermal and shear degradation during melt processing of PVAL limited the use of conventional thermoplastic melt technology. Application of PVAL was limited to aqueous solutions and cast ﬁlms. However, advances in PVAL polymer formulation mean that the properties of PVAL can now be retained during thermoplastics processing and it is possible to produce water-soluble, non-toxic, biodegradable plastics by conventional thermoplastics forming techniques. A brief description of some of these techniques follows.
Process for producing either pellets for other heat forming processes such as injection moulding, sheets (which can also be used for thermoforming) or proﬁles such as tubes, pipes and rods.
Process for producing thin ﬁlms products such as shrink wraps and carrier bag ﬁlm.
High shear and pressure process for production of complex and mass produced components such as mobile phone covers, lids, automotive door handles, motorcycle helmets.
Low pressure process which deforms sheet material into relatively simple shapes such as trays, cups and shallow tubs.
Inﬂation production process which produces hollow articles such as bottles, containers and tanks.
Production of thin ﬁbre strand produced from molten plastic passed through a multi-holed proﬁle. (This is not to be confused with spinning from a solution, as in the production of Vinylon ﬁbre or electrospinning which produces PVAL nano-fibres and is also a solution process.)
PVAL melt processing temperatures tend to range between 180 and 240 °C. This depends on the level of hydrolysis and speciﬁc formulation and additives used. Generally fully hydrolysed grades, which have higher melting points, require higher temperatures to be used. They also tend to be harder to process. To improve the processibility of PVAL it is necessary to use a plasticiser and lubricants which lower melt temperature and viscosity and therefore allow lower processing temperatures to be utilised. The degree of degradation is strongly inﬂuenced by acetate groups which liberate acetic acid during processing which catalyses further degradation to occur. Higher levels of hydrolysis 98 mol% are more resistant to degradation that 88 mol%. Temperature rather than shear appears to be a dominant factor in this.
In such applications, the basic PVAL must be plasticised so as to reduce its melting point, and obtain a thermal processing window for processing. In general plasticisers, such as glycerol, polyethylene glycol, sorbitol and other compounds have been used.
Mowiﬂex TC is an example of a thermoplastic melt processable material currently sold by Kuraray. This can be used to produce blown and sheet ﬁlm as well as injection moulded components. As expected of PVAL, it is moisture sensitive and sold in moisture resistant bags, however, it can be dried if needed at 60-80 °C for 6-8 hours using conventional air drying equipment. Therefore, it can be treated like other moisture sensitive materials such as Nylon routinely used in processing.
Tubing and hoses produced by extrusion retain many of the properties recognisable from solution processing. They are highly ﬂexible and retain excellent solvent resistance to oils, greases and other chemicals. Processing is carried out on standard extruders with low residence times. Keeping residence times as low as possible is one key factor in successful processing of PVAL materials. Thermal damage produces discoloration of PVAL products, as it does with many other thermoplastic components.
8.2 Injection Moulding
For injection moulding of PVAL, recommended mould tool temperatures are in the 70-80 °C range with melt temperatures ranging from 190-220 °C. This is similar
to parameters used to process polyethylenes. This can be performed on conventional equipment using hot or cold runners to produce a variety of moulded components. With the fast cycling time possible with injection moulding it is possible to mass produce a variety of components and products very rapidly and economically.
An example component is exhibited in the Science Museum, London, UK. This is a biodegradable mobile phone casing developed by researchers at the University of Warwick's, Warwick Manufacturing Group, in conjunction with PVAXX Research & Development Ltd. A water soluble mobile phone case was the component. However, this idea had a twist. By imagining the components end-of-life and burying the case after use with a sunﬂower seed beneath it, the phone biodegraded and the sunﬂower seed began to grow and eventually ﬂowered. This was timed with the growing awareness of the problem of plastic waste and sustainability, as well as the newly introduced European Union WEEE Directive (waste electrical and electronic equipment) (a.8) which covered the ever growing problem of electrical waste. Therefore, discarded mobile phones were a hot topic and this application captured public attention. However, problems of water prooﬁng the product for use (in rain or wet environments for instance), mean as yet this application is not in commercial production.
8.3 Film Moulding
An extrudable PVAL material for blown ﬁlm application was marketed by A. Schulman, Akron, USA under the name Aquasol. It is reported to have the same physical properties as the cast ﬁlm and could be used in conventional polyoleﬁn melt equipment. The target market to be biodegradable replacement for LDPE (a.9). Most of the market in these ﬁlm applications is for disposable packaging.
Table 6 shows a typical range of properties shown by
various grades of PVAL in comparison to other ﬁlm materials. Most marked here is the tear strength and tensile strength which is actually comparable to that produced by a polypropylene material. PVAL materials also show good puncture resistance and impact strength. However performance is markedly affected by the degree of hydrolysis and therefore the crystallinity of the base material as well as the molecular weight, distribution and branch structure.