Polymer rheology retardation process

A major drawback to the industrial use of fire-retardant fillers is the high addition levels needed in most polymers to confer adequate fire retardancy. This can detrimentally influence processability and melt rheology, and, when used in load-bearing situations, the presence of the filler generally... 

Any additive is a potential source of change to the overall processability from pellet feed to melt rheology. The not uncommon operator comment that one particular color always runs well and another always causes problems is more likely to be fact than superstition. Many products are colored by using masterbatches. whilst extruded products may contain antiblock and slip additives. Injection moldings may contain lubricants to aid mold release or provide product lubrication, e,g., bottle caps. In many cases such nias-terbatches contain low-viscosity polymer waxes to promote additive dispersion (particularly pigments) and masterbatch distribution throughout the natural polymer. There are in fact many additives, including fillers, flame retardants, and antioxidants, that can influence processability. 

Since it is evident from discussions in previous chapters that nanodispersed, functionalized, largely inert particles such as clays and synthetic alternatives cannot promote sufficient flame retardant activity alone but only in the presence of more conventional flame retardants, their potential usefulness will be determined by their ease of processing and the manner in which they influence both process and end product. Essential issues to be considered and resolved are nanoparticle compatibility with the polymer matrix and other additives present, the ability to maintain a nanodispersion during all processing stages, their influence on rheology, and the possible compromise between effective concentrations levels and optimization of these. 

In Chapter 7 the combination of nanocomposites with metal hydroxide flame retardants has generally been discussed. Since the use of metal hydroxide usually requires very high concentrations within the polymer matrix (often higher than 50% w/w), to achieve desired levels of flame retardancy as noted above regarding the work of Beyer, - the influence on rheology and hence processability can be significant. Hornsby and Roflion have discussed this issue and they report that compounded polymer melt viscosities and shear sensitivities, for example. 

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