Plasticised polymer films

Table 7.7 The composition and room temperature conductivity of some solid poiymer eiectroiytes (SPEs) and plasticised polymer films...

The diffusion and the permeability are inversely related to the density, degree of crystallinity, orientation, filler concentration, and crosslink density of a polymeric film. As a general rule, the presence of plasticisers or residual solvents increases the rate of diffusion in polymers. Films cast from poor solvents have high permeability. The rate of diffusion or permeability is independent of the molecular weight of the polymer, providing the polymer has a moderately high molecular weight. 

Most polymer membrane ISEs are prepared by dissolving an ionophore in a polyvinylchloride (PVC) membrane. A large variety of plasticisers are used to increase the dielectric constant of the PVC and improve its hydrophilicity. Some membranes have complexes of the ions to be sensed to increase membrane conductivity, such as potassium tetraphenylborate in K -selective membranes. There is an extensive literature on the arcane arts of polymer membranes for electrodes with dissolved ionophores and a good review of this is given by Professor Ronald Armstrong in Section 3.7 of Gabor Harsanyi s book. Polymer films in sensor applications [14]. 

Additional tests for polymer films that have been mentioned in the literature are the tear strength of ethylene-vinyl acetate plasticiser [108], coefficient of friction of polyolefin plasticiser blown film [109], and oxygen absorption in food packaging films [110]. 

If the two bath temperatures have been chosen correctly, the emulsion will dry to a continuous film at the hot end of the bridge and will be cracked and crazed at the cold end. The boundary between the cracked and intact films occurs at the minimum film forming temperature. The MFFT is generally slightly lower than the Tg because of the plasticising effect of water on the polymer film. 

The MFFT of the emulsion as formulated must be lower than any tempoature at which the paint is likely to be applied. For an indoor paint in the UK it is unlikely that temperatures below 10°C will be encountered, whilst the outdoor limit might be 5°C. Damage to paint films can occur should the ambient temperature fall below the Tg of the film. The Tg of a hard polymer, such as vinyl acetate, styrene or methyl methacrylate, can be reduced either by copolymerisation with a soft monomer or by adding an external plasticiser, such as butyl phthalate. On a cost effective basis external plasticisation is better for reducing the Tg. The snags are, firstly, that plasticisers are slowly lost through evaporation and, secondly, they can also diffuse into the substrate. The use of an internally plasticised polymer overcomes both problems and also saves the processing time necessary to incorporate an external plasticiser. 

Polyesters are eneountered in many forms. They are important as laminating resins, moulding compositions, fibres, films, surface coating resins, rubbers and plasticisers. The common factor in these widely different materials is that they all contain a number of ester linkages in the main chain. (There are also a number of polymers such as poly(vinyl acetate) which contain a number of ester groups in side chains but these are not generally considered within the term polyester resins.)... 

However, this structure does not give the same properties, and the polymer degrades slowly, eliminating HCl. Plastisols (PVC -t- plasticiser) lose gloss rapidly and gradually chalk even in temperate climates, but the high film thicknesses that lower cost permits lead to long life. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Figure 5 shows the separation of the plasticiser components present in a PVC-based cling film. The sample was first dissolved in tetrahydrofuran and then the components present separated by size exclusion chromatography (SEC) using mixed bed-E columns (Polymer Laboratories) and tetrahydrofuran eluting solvent. IR spectra of the separated components were then obtained using "LC-Transform " (Lab Connections) equipment. Components as they elute from... 

Organic peroxide are used to polymerise the esters by solvent or emulsion polymerisation. They form tough and pliable film. They are also used as plasticising agents for vinyl polymers. The polymer is soluble in benzene, toluene, chloroform, ethylene dichloride, ethyl acetate, etc. 

ICI has developed a fermentation process for PHB having various levels of polyhy-droxyvalerate (PHV) as a copolymer. This polymer is marketed under the product name BIOPOL. The material is extrudable and can be used as bottles for packaging cosmetics. Because of the high migration rate of the triacetine plasticiser used (see Chapter 4) it is not suitable for food use. Currently efforts are being made to manufacture this material as a film. 

Vinyl chloride can be polymerised to form polyvinyl chloride (PVC) which is fairly brittle and unsuitable for food contact applications, so it is mixed with plasticisers to soften the polymer and impart flexibility. Plasticised PVC may contain about 30% of plasticisers and is used to make stretch films and flexible PVC. Flexible PVC used for tubing and gaskets may contain di(2-ethylhexyl)phthalate, and stretch films will probably contain di(2-ethylhexyl)adipate and a polymeric adipate plasticiser. Rigid PVC may... 

It is possible to accelerate the rate of the polycondensation reaction by incorporation of special catalysts, resulting in urethane-urea-modified epoxy resin. The low-volatility alkyl phenol liberated in this reaction remains in the film as an external plasticiser. Owing to the different rates of the above two reactions, they have been synchronised to produce suitable polymer segments (Figure 10.9). 

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