Polymers compounding

TABLE 11.1 Calculated Interphase Thicknesses 5/ for Four Pairs of Immiscible Polymers 

Apparently, with a very small interphase thickness the two end-cap groups are too few and not easily accessible to affect compatibilization. On the other hand, when four anhydride (An) groups are attached, randomly on each PDMS chain, then the blend of 20% PDMS/4-An and PA 6/di-amine have a very fine and stable morphology (ca 0.5 pm). Thus, the amount of interfacial reaction product, although diminished by small / values of the unmodified polymer components, is promoted by the larger number and more accessible functional groups in either or both of the reactive components. Finally, Macosko and co-workers (62) have estimated that the minimum fraction of the interphase that has to be covered by reacted compatibilization products to achieve fine and stable morphologies is about 0.2. 

TABLE 11.2 Examples of Additives that Modify Mechanical Properties, Electrical Conductivity, and Flame Retardancy 

Inorganics Oxides (glass, MgO, Si02, A1203) Hydroxides (Al(OH)3) Salts (CaC03, BaS04, CaS04, phosphates) Silicates (talc, mica, kaolin, woolastonite) Metals (boron, steel fibers) 

Organics Carbon-graphite, cellulose, PA, PET, PE, PVA and aramid fibers, wood starch 

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In selecting a flame retardant for a given appHcation, the cost contribution of the flame retardant to the final polymer compound must be taken into account. Assessment of cost should be done on a cost per volume basis rather than a simple cost per weight basis. 

Accelerator activators are chemicals required to initiate the acceleration of the curing process. They also improve the polymer compound quaUty. 

Hypalon raw polymer compounds or cured product may be disposed of in an approved landfill. Incineration is not recommended because of the evolution of toxic gases. Additional information is available from Du Pont concerning these and other potential health hazards when handling Hypalon compounds, finished products, thermal decomposition products, or waste disposal (43). 

Since the incorporation of plasticisers into a polymer compound brings about a reduction in glass temperature they will also have an effect on the electrical properties. Plasticised PVC with a glass temperature below that of the testing temperature will have a much higher dielectric constant than unplasticised PVC at the same temperature (Figure 6.6). 

Table 7.1 summarises the blooming expectancies of additives in polymer compounds but it should be stressed that there may be exceptions to these very general rules. 

Particulate fillers are divided into two types, inert fillers and reinforcing fillers. The term inert filler is something of a misnomer as many properties may be affected by incorporation of such a filler. For example, in a plasticised PVC compound the addition of an inert filler will reduce die swell on extrusion, increase modulus and hardness, may provide a white base for colouring, improve electrical insulation properties and reduce tackiness. Inert fillers will also usually substantially reduce the cost of the compound. Amongst the fillers used are calcium carbonates, china clay, talc, and barium sulphate. For normal uses such fillers should be quite insoluble in any liquids with which the polymer compound is liable to come into contact. 

It has been common practice to blend plasticisers with certain polymers since the early days of the plastics industry when Alexander Parkes introduced Parkesine. When they were first used their function was primarily to act as spacers between the polymer molecules. Less energy was therefore required for molecular bond rotation and polymers became capable of flow at temperatures below their decomposition temperature. It was subsequently found that plasticisers could serve two additional purposes, to lower the melt viscosity and to change physical properties of the product such as to increase softness and flexibility and decrease the cold flex temperature (a measure of the temperature below which the polymer compound loses its flexibility). 

At the time of writing photodegradants are in an early stage of development and have not yet been fully evaluated. It is a moot point whether or not manufacturers will put such materials into polymer compounds and thus increase the price about 5% without legal necessity. However, if such legislation, considered socially desirable by many, took place one might expect polyethylene... 

Polymer compounds vary considerably in the amount of heat required to bring them up to processing temperatures. These differences arise not so much as a result of differing processing temperatures but because of different specific heats. Crystalline polymers additionally have a latent heat of fusion of the crystalline structure which has to be taken into account. 

As has been mentioned in earlier chapters polymers vary enormously in their thermal stability. Before attempting to process any specific polymer compound its thermal stability characteristics should be considered. The most important questions to be answered are ... 

For this reason tribasic lead sulphate, a good heat stabiliser which gives polymer compounds with better electrical insulation properties than lead carbonate, has increased in popularity in recent years at the expense of white lead. Its weight cost is somewhat higher than that of lead carbonate but less than most other stabilisers. This material is used widely in rigid compounds, in electrical insulation compounds and in general purpose formulations. 

Compared with more common plastics used as packaging materials, the compound does have some disadvantages, such as a high water vapour permeability and limited heat resistance, losing dimensional stability at about 70°C. It is also substantially more expensive than the high-tonnage polyolefins. Last but not least its biodegradability means that it must be used in applications that will have completed their function within a few months of the manufacture of the polymer compound. 

Part 1 (1978) Symbols for terms relating to homopolymers, copolymers and polymer compounds. 

Report 139 Rubber Analysis - Polymers, Compounds and Products, M.J. Forrest, Rapra Technology Ltd. 

TABLE 2 Effect of Injection Molding Temperature on 3,9-Bis-(ethylidene-2,4,8,10-tetraoxaspiro[5,5]undecane), (75 25) 1,6-Hexanediol / trans - Cyclohexanedimethanol Polymer Compounded with 3 wt% Phthalic Anhydride and 7.5 wt% Cyclobenzaprine Hydrochloride (CBP)... 

To obtain representative samples from nonhomoge-neous sample materials, such as polymer compounds, particle-size reduction techniques need often to be applied (not for film) [50]. Also, for destructive inpolymer additive analysis it is advantageous to change the physical state of solid samples to provide a larger surface area per unit mass. Complete extraction is sometimes achieved only after grinding the sample. Typically, Perlstein [51] has reported recoveries of only 59 % for extraction of Tinuvin 320 from unground PVC after 16 h of Soxhlet extraction with diethyl ether while recoveries rise to 97 % for ground polymer. 

Nowadays, MS is often no longer the analytical bottleneck, but rather what precedes it (sample preparation) and follows it (data handling, searching). Direct mass-spectrometric methods have to compete with the separation techniques such as GC, HPLC and SFC that are commonly used for quantitative analysis of polymer additives. Extract analysis has the general advantage that higher-molecular-weight (less-volatile) additives can be detected more readily than by direct analysis of the polymer compound. 

Direct polymer compound analysis by soft ionisation, tandem MS/MS and high-resolution (AC-MS) mass spectrometry, has been reviewed [236]. 

Direct Mass-Spectrometric Polymer Compound Analysis... 

DIRECT MASS-SPECTROMETRIC POLYMER COMPOUND ANALYSIS... 

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