Rubber-toughened blends

Figure 7. TEM images of rubber-toughened blends made by sequential blending ...

HIPS polymers consist of a matrix of polystyrene containing approximately spherical particles of rubbery polybutadiene ranging in size from about 0.1 to 10 pm depending on the precise composition and method of polymerisation. The rubber particles may themselves contain small regions of PS as shown in fig. 12.7. Another series of rubber-toughened blends is the acrylonitrile-butadiene-styrene (ABS) terpolymers, which are basically... 

It was postulated (Bucknall and Paul 2009) that the same equation can be used also for the approximation of yield in pure shear of rubber-toughened blends, which contain only void-free rubber particles or the combination of cavitated and void-free particles with the total volume fraction of intact and cavitated particles < )... 

Crazing is a mechanism of plastic deformation that is extremely localized. Even when the number of crazes in the sample is substantially increased, as in the case of multiple crazing in rubber-toughened blends, their early stages of development... 

The important factors that affect the rubber toughening are (1) interfacial adhesion, (2) nature of the matrix, (3) concentration of the rubber phase, and (4) shape and size of the rubber particles. In the PS-XNBR blend containing OPS, due to the reaction between oxazoline groups of OPS and carboxylic groups of XNBR, the interfacial adhesion increases and as a result, the minor rubber phase becomes more dispersed. The immiscible blend needs an optimum interfacial adhesion and particle size for maximum impact property. In PS-XNBR, a very small concentration of OPS provides this optimum interfacial adhesion and particle size. The interfacial adhesion beyond this point does not necessarily result in further toughening. 

Figure 14.7 Schematic highlighting the microstructure of rubber-toughened PET and performance improvements when non-reactive elastomers are blended with reactive elastomers (adapted from Atofina literature entitled Lotader and Lotryl )...

ABS Three-component copolymer of acrylonitrile, butadiene, and styrene, alloy Rubber-toughened materials in which the matrix can be a mixture of polymer tyrpes. alternation copolymer Ordered copolymer in which every other building is a different mer. azeotropic copolymer Copolymer in which the feet and composition of the copolymer are the same, blends Mixtures of different polymers on a molecular level may exist in one or two phases, block copolymer Copolymer that contains long sequences or runs of one mer or both mers. 

Rubber-toughened polystyrene composites were obtained similarly by polymerising the dispersed phase of a styrene/SBS solution o/w HIPE [171], or a styrene/MMA/(SBS or butyl methacrylate) o/w HIPE [172], The latter materials were found to be tougher, however, all polymer composites had mechanical properties comparable to bulk materials. Other rubber composite materials have been prepared from PVC and poly(butyl methacrylate) (PBMA) [173], via three routes a) blending partially polymerised o/w HIPEs of vi-nylidene chloride (VDC) and BMA, followed by complete polymerisation b) employing a solution of PBMA in VDC as the dispersed phase, with subsequent polymerisation and c) blending partially polymerised VDC HIPE with BMA monomer, then polymerisation. All materials obtained possessed mixtures of both homopolymers plus some copolymer, and had better mechanical properties than the linear copolymers. The third method was found to produce the best material. 

The preferred average particle size 1n HIPS was believed to be 0.8 ijm (J.). However, our current data indicate that a number average particle diameter of 1.05 urn and 0.5 -urn appear to be a preferred size for HIPS and rubber-toughened polypropylene (PP), respectively. The morphology of the rubbery phase in a toughened PP appears to be less complex, as evidenced in Figure 2 where the dark, also osmium-stained, phase is the styrene-butadiene rubber (SBR) particles. No PP occlusions were found in this material since it is a physical blend of SBR and PP. 

A blend was prepared by dissolving a rubber material in styrene and polymerizing the system. The blend contains not only rubber and polystyrene (PS), but also a graft polymer because of the attachment of short polystyrene side chains to the rubber molecules. The toughness of this material was markedly improved compared to that of the unmodified PS. A technology based on bulk polymerization [26] has been widely used the concentrated emulsion polymerization method employed by us, however, allows one to obtain rubber toughened latexes. 

According to Partridge [163], toughening is efficient when, by comparison to the neat homopolymer tested under the same conditions, the impact resistance is multiplied by a factor of 10, without losing more than 25% of stiffness. The upper temperature limit for the use of rubber-modified blends is controlled by the matrix melt temperature, Tm, their lower limit by the glass transition temperature, Tg, of the particles. As soon as the viscoelastic response of the latter is too slow to accommodate an external loading, the polymer assumes a glassy state and breaks in a brittle way. 

Fig. 23 Flexural impact strengths of /S-modified rubber toughened PP plotted versus the amount of rubber content of the blends and the testing temperature. The arrows indicate samples that did not break. Data taken from Varga [165]...

Bucknall CB (2000) Deformation mechanisms in rubber-toughened polymers. In Paul DR and Bucknall CB (eds) Polymer Blends, Vol 2. Wiley, New York p 83... 

Abstract The effects of the amount of rubber, the concentration of fibres and the state of the fibre/matrix interface upon the mechanical behaviour of short glass fibre-reinforced rubber-toughened nylon 6 ternary blends are described. First, tensile tests were carried out on different intermediate materials and then on the ternary blends to derive the stress-strain curves and document the damage mechanisms. Fracture toughness tests were implemented on compact tension specimens and the results were correlated to fractographic observations and acoustic emission analysis to assess the role of the different constituents. 

Keywords rubber-toughened thermoplastic glass fibre ternary blends mechanical tests fracture toughness J-integral image analysis fractographic observations acoustic emission. 

The characteristic values of the crack initiation and propagation parameters (Jic, Kjc and Tr) are listed in Table IV for the different ternary blends. In all cases the requirements for valid fracture toughness measurement were fulfilled. These results confirm that type B fibres are better suited as reinforcement for rubber-toughened nylon materials. But the marked reduction... 

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