Blended polymers impact resistance, incompatibility

Where the two phases are completely compatible, a homogeneous polyblend results which behaves like a plasticized resin (one phase). If two polymers are compatible, the mixture is transparent rather than opaque. If the two phases are incompatible, the product is usually opaque and rather friable. When the two phases are partially compatibilized at their interfaces, the polyblend system may then assume a hard, impact-resistant character. However, incompatible or partially compatible mixtures may be transparent if the individual components are transparent and if both components have nearly the same refractive indices. Furthermore, if the particle size of the dispersed phase is much less than the wavelength of visible light (requiring a particle size of 0.1/a or less), the blends may be transparent. 

Despite the incompatibility of silicone towards many polymers, several techniques have been more or less successfully developed to produce silicone containing physical blends. Although compatibilization remains essentially of academic interest only, many industrial applications for IPNs are a testimony to their growing importance. Silicone blends allow researchers to introduce specific properties such as impact resistance or low surface energy to polymers that fundamentally lack these characteristics. On the other hand, it must be acknowledged that silicone blends and related fields of research are still open to further development and will undoubtedly lead to a wide range of future industrial applications. 

PVCH Blends With Hydrogenated SB Polymers. One early goal of this research was to find a polymer that could be blended with PVCH to give an impact resistant product. Conventional unsaturated rubbers were incompatible. We did find, however, that PVCH-containing copolymers were compatible with PVCH and could yield clear, tough plastic compositions as shown in Table VIII. To obtain transparency, a minimum of 15% of a 25% PVCH compolymer is required. Depending on the ratios of PVCH to the copolymer, tough heat-resistant products can be made. 

Compatibilisers make two largely incompatible polymers mix together to form a new blend or alloy. There has been a steep rise in demand for them in recent years, because polymer blends provide a fruitful way to tailor polymer properties to specific applications. They have also led to improved impact modifiers which, being polymeric, must form a blend whenever they are used. Some of the newer alloys, such as Rhodia s PA/ABS and Crompton s PP/SEBS, are highly impact-resistant. Compatibilisers are also used to improve the properties of mixed plastics waste and to compatibilise polymers with wood or mineral fillers. 

Compatibilizers are frequently materials such as block or graft copolymers. A specific example would be a copolymer comprising two blocks where each is compatible with one component of the blend (in a blend of two plastics) and incompatible with the other. An A-x-B block copolymer, where A and B are long sequences of monomer that are identical to the corresponding A and B polymers forming the blend, and X is a bond between the blocks, is one of the simplest forms of compatibilizer. A functionalized polymer where the main polymer is compatible in one phase and the functionality is compatible in the other phase would be another example of a compatibilizing agent. One example of such a material would be maleic anhydride functionalized polypropylene (PP-MA) used to compatibilize blends of PP and Nylon 66. Recent advances in the production of PP-MA have seen an increase in the impact resistance of... 

Immiscible polymer blends were prepared by melt extmsion using a single screw extmder in the systems PS/HDPE and PS/PP to assess the effect of composition and morphology on tensile Young s modulus and impact resistance. Results from the work show that tensile modulus nearly follows rule of mixture behavior for both systems, although better performance is shown by the PS/PP blends. With regard to impact resistance, the PS/HDPE system showed poor, incompatible performance, whereas excellent impact resistance was noted in the PS/PP blends. 

Commercial PPE/PA blends were developed by the motivation to combine the high heat resistance characteristics of PPE with the chemical resistance characteristics of the crystalline polyamide polymers (PA-66 and PA-6). Because of the inherent incompatibility between PPE and polyamides, suitable methods of compatibihzation and toughening have not been developed until recently. The technology of compatibihzed, impact-modi-... 

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