LITERATURE REVIEW
3.3 Reactivity Studies Using Extrusion Plastometer
The second stage of this research covers the evaluation of reactivity between functional groups of the compatibilisers using a Tinius Olsen MP987 extrusion plastometer (also known as melt indexer). Figure 3.3 shows a schematic representation of a typical extrusion plastometer which consists of a heated barrel, an orifice at the bottom of the barrel, a piston and a dead weight for pushing the melt out of the heated barrel through the orifice.
In this study, the extrusion plastometer was used as a “reactor” since it allows a fixed amount of polymer mixture to reside in a uniformly heated barrel for a fixed residence time, temperature and load. Any reactions that took place in the barrel could result in a change in viscosity of the melt leading to changes in the melt flow rate of the sample under constant test conditions.
Figure 3.3 Schematic representation of an extrusion plastometer (melt indexer)
In order to ensure that the mixtures were homogenously mixed in the heated barrel, all HDPE and HDPE-g-MAH pellets were pulverised using a Retsch
Piston
Thermocouple Heatimg Bands
Orifice Melt
Insulation Reference
Marks Weight
Piston
Thermocouple Heatimg Bands
Orifice Melt
Insulation Reference
Marks Weight
ultra centrigual mill ZM 200 to grain size of about 1 mm. The epoxy flakes which are brittle under room conditions were physically ground into powder using mortar and pestle. The powder mixtures were weighed and hand mixed in a plastic bag in a sample batch size of 100 g.
During the melt flow rate tests, 6 g of each homogenous powder mixture was loaded into the barrel and heated at 190°C with pre -heating dwell times of 5 and 15 minutes under a standard load of 2.16 kg. The extrudates obtained after the pre-heating time were weighed and melt flow rates expressed in grams per 10 minutes were obtained by dividing the mass of the extrudate by the time interval (in seconds) used in obtaining the extrudate and then multiplied by 600. All melt flow rates reported in this study are average of 3 determinations (see Appendices B3-1 to B3-3). Extrudates collected from the extrusion plastometer were used for further characterisation such as DSC, FTIR, optical microscopy and solvent extraction.
Blends of varying ratios of HDPE with HDPE-g-MAH in Table 3.9 were evaluated for the possible influence of pre-heating time in the extrusion plastometer on the flow behaviour of the blends. They also served as basis for detecting any reaction when epoxy was added.
Table 3.9 Powder dry blends of HDPE/HDPE-g-MAH Sample
Code Sample Composition HDPE
(wt%)
HDPE-g-MAH (wt%)
HDPE-M1 HDPE/HDPE-g-MAH 50 50 (0.5)
HDPE-M2 HDPE/HDPE-g-MAH 75 25 (0.25)
HDPE-M3 HDPE/HDPE-g-MAH 90 10 (0.1)
HDPE-M4 HDPE/HDPE-g-MAH 95 5 (0.05)
Figures in parenthesis denote active content (wt%) of maleic anhydride
Similarly, blends of HDPE with varying amounts of epoxy resin as shown in Table 3.10 was evaluated for possible influences of the epoxy on the flow rate of the HDPE without interaction (before the addition of HDPE-g-MAH).
Table 3.10 Powder dry blends of HDPE/epoxy Sample
Code Sample Composition HDPE (wt%) Epoxy (wt%)
HDPE-E1 HDPE/epoxy 94 6.0
HDPE-E2 HDPE/epoxy 97 3.0
HDPE-E3 HDPE/epoxy 98.8 1.2
HDPE-E4 HDPE/epoxy 99.4 0.6
3.3.1 Stoichiometry Considerations
The components used in the reactive formulations were calculated stoichiometrically as follows:
a.) Determination of MAH concentration:
The commercial grade of HDPE-g-MAH used in this study contains 1 wt% of grafted MAH. Thus if 10 grams of this HDPE-g-MAH is used in a formulation based on 100 grams sample, it should contain 0.1 gram of active grafted
b.) Determination of catalyst (hydrated zinc acetate) concentration:
In order for maleic anhydride to react with the epoxy, it has to be first converted into carboxylic acid through a hydrolysis reaction with water. This can be achieved by the addition of hydrated zinc acetate as a catalyst which releases the required amount of water during processing.
Basic information:
• Molecular weight of hydrated zinc acetate (CH3COO)2Zn * 2H2O): 219.49 gmol-1
• Molecular weight of H2O = 18 gmol-1
• Percentage of H2O present in hydrated zinc acetate: [(2 x 18 gmol-1) / 219.49 gmol-1] x 100% = 16.4 wt%
To obtain 0.00101 mole of H2O, (0.00101 mole x 18 gmol-1) = 0.01818 gram is needed.
Since the hydrated zinc acetate contains 16.4 wt% of water, [(0.01818 g x 100 wt%) / 16.4 wt%] = 0.11 gram of hydrated zinc acetate is required to produce 0.00101 mole of water.
Therefore in 100 grams of sample formulation that contains 10 grams of HDPE-g-MAH i.e. 0.00101 moles of grafted MAH moieties, 0.11 gram of hydrated zinc acetate catalyst is required to achieve an equimolar reaction.
An example of a formulation having equimolar concentration of MAH and catalyst is HDPE-ME3C in Table 3.11.
c.) Determination of DGEBA concentration:
The equivalent weight of DGEBA epoxy resin used in this study is approximately 595 gEq-1 and since the functionality of the linear epoxy resin is 2, the molecular weight is thus approximately equal to, (595 gEq-1 x 2) = 1190 gmol-1. This also corresponds to the n value (degree of polymerisation) of 3 for the DGEBA provided by the supplier.
Based on 100 grams of sample, in order to obtain the same molar concentration of MAH (0.00101 moles), the amount of DGEBA needed will be (0.00101 mole x 1190 gmol-1) = 1.2 grams. Therefore, for every 0.1 gram of MAH moiety present in the formulation, 1.2 grams of DGEBA will be needed for an equimolar reaction. An example of formulation having an equimolar concentration of MAH and epoxy moieties is HDPE-ME3 in Table 3.11.
After obtaining the stoichiometric ratios of the MAH, epoxy and catalyst components, the various formulations presented in Table 3.11 were evaluated for the effect of molar ratio of MAH:epoxy, and also the influence of catalyst on the esterification of the MAH and epoxy.
Table 3.11 Powder dry blends of catalysed and uncatalysed HDPE/HDPE-g-MAH/epoxy
Sample Code Sample Composition Active Components in Blends (wt%) HDPE-g-MAH Epoxy Catalyst*
HDPE-ME1 HDPE/HDPE-g-MAH/epoxy 50 (0.5) 6.0 -
HDPE-ME1C HDPE/HDPE-g-MAH/epoxy/cat. 50 (0.5) 6.0 0.55
HDPE-ME2 HDPE/HDPE-g-MAH/epoxy 25 (0.25) 3.0 -
HDPE-ME2C HDPE/HDPE-g-MAH/epoxy/cat. 25 (0.25) 3.0 0.28
HDPE-ME3 HDPE/HDPE-g-MAH/epoxy 10 (0.1) 1.2 -
HDPE-ME3C HDPE/HDPE-g-MAH/epoxy/cat. 10 (0.1) 1.2 0.11 HDPE-ME3Ca HDPE/HDPE-g-MAH/epoxy/cat. 10 (0.1) 3.0 0.11
HDPE-ME4 HDPE/HDPE-g-MAH/epoxy 5 (0.05) 0.6 -
HDPE-ME4C HDPE/HDPE-g-MAH/epoxy/cat. 5 (0.05) 0.6 0.06 HDPE-ME4Ca HDPE/HDPE-g-MAH/epoxy/cat. 5 (0.05) 3.0 0.06 Figures in parenthesis denote active content (wt%) of maleic anhydride
*Hydrated zinc acetate catalyst
From the results of evaluation on the extrudates of these blends, the most promising blend was selected for scaling up and further modification on the twin screw extruder. The short-listed formulations from this section of work for scaling up were presented earlier in Table 3.4.