Acrylic plastics mechanical properties

An important subdivision within the thermoplastic group of materials is related to whether they have a crystalline (ordered) or an amorphous (random) structure. In practice, of course, it is not possible for a moulded plastic to have a completely crystalline structure due to the complex physical nature of the molecular chains (see Appendix A). Some plastics, such as polyethylene and nylon, can achieve a high degree of crystallinity but they are probably more accurately described as partially crystalline or semi-crystalline. Other plastics such as acrylic and polystyrene are always amorphous. The presence of crystallinity in those plastics capable of crystallising is very dependent on their thermal history and hence on the processing conditions used to produce the moulded article. In turn, the mechanical properties of the moulding are very sensitive to whether or not the plastic possesses crystallinity. 

Several flexible polymers, such as natural rubber (NR) synthetic rubber (SR) polyalkyl acrylates copolymers of acrylonitrile, butadiene, and styrene, (ABS) and polyvinyl alkyl ethers, have been used to improve the impact resistance of PS and PVC. PS and copolymers of ethylene and propylene have been used to increase the ductility of polyphenylene oxide (PPO) and nylon 66, respectively. The mechanical properties of several other engineering plastics have been improved by blending them with thermoplastics. 

The application of polymeric plasticizers can be effected by mixing a preformed polymer mechanically with a polymerizable monomer containing the catalyst and subsequent polymerization. But side reactions, like grafting, must be expected. Generally, this method has not found wide application because the resulting products are likely to show poor mechanical properties. Besides, mixing the monomer on the rolls or in the extruder leads to losses by evaporation and causes unpleasant odors. Furthermore, some of the more important monomers, like the acrylates, show poor compatibility with many polymers. For instance, PVC is not sufficiently plasticizable with acrylates. 

This study was therefore undertaken to prepare and evaluate acrylonitrile—butadiene-styrene (ABS) and methyl methacrylate-butadiene-styrene (MBS) polymers under similar conditions to determine whether replacement of acrylonitrile by methyl methacrylate could improve color stability during ultraviolet light aging, without detracting seriously from the good mechanical and thermal-mechanical properties of conventional ABS plastics. For purposes of control, the study also included briefer evaluation of commercial ABS, MBS, and acrylonitrile-butyl acrylate-styrene plastics. 

High-brisance crystalline explosives, such as RDX or octogen, can be embedded in curable or polyadditive plastics such as polysulfides, polybutadiene, acrylic acid, polyurethane, etc. The mixture is then cured into the desired shape. Other components such as aluminum powder can also be incorporated. The products obtained can be of any desired size, and specified mechanical properties can be imparted to them, including rubber-like elasticity (-> LX and -> PBX). They can also be shaped into foils. 

The mechanical properties of rapidly polymerizing acrylic dispersions, in simulated bioconditions, were directly related to microstructural characteristics. The volume fraction of matrix, the crosslinker volume in the matrix, the particle size distribution of the dispersed phase, and polymeric additives in the matrix or dispersed phase were important microstructural factors. The mechanical properties were most sensitive to volume fraction of crosslinker. Ten percent (vol) of ethylene dimethacrylate produced a significant improvement in flexural strength and impact resistance. Qualitative dynamic impact studies provided some insight into the fracture mechanics of the system. A time scale for the elastic, plastic, and failure phenomena in Izod impact specimens was qualitatively established. The time scale and rate sensitivity of the phenomena were correlated with the fracture surface topography and fracture geometry in impact and flexural samples. 

Using tensile testing of free films, researchers have shown that plasticizer type and concentration influence the mechanical properties of both acrylic and cellulosic polymers. ° Fig. 10 shows the influence of dibutyl sebacate concentration on the tensile properties of free ethyl cellulose films. ° As the concentration of the... 

Gutierrez-Rocca, J.C. McGinity, J.W. Influence of water soluble and insoluble plasticizers on the physical and mechanical properties of acrylic resin copolymers. Int. J. Pharm. 1994, 103, 293-301. 

Hauser et al. [1993] claim that articles for medical and other uses made from a polymer alloy of a clear styrenic acrylate, a ductile styrene-diene polymer, and a rubbery block styrene-diene copolymer may be sterihzed by gamma irradiation, without significant increase in its yellowness index or significant deterioration of the alloy s mechanical properties (Table 11.9). There are many applications, e.g., urine sample botdes, items in space probes, and cosmetic containers, that are made from transparent plastics and need to be radiation-sterihzed. However, many clear plastics do develop color on irradiation, and their mechanical properties tend to deteriorate, particularly on irradiation in air. Hauser et al. 

Resins with varying properties from toughened plastics to high elongation elastomers can be formed. Many acrylate thiol hybrid polymerizations that result in modifications of mechanical properties of the polymeric network are... 

MABS is similar to ABS except for the addition of an additional monomer, usually methyl methacrylate. MABS is an amorphous, clear, transparent material with thermal and mechanical properties like ABS. The transparency is achieved by matching the refractive indices of the matrix resin (the transparent acrylate—acrylonitrile—styrene polymer) with the polybutadiene rubber impact modifier. MABS has the highest impact resistance of all the styrenic plastics. Sometimes called transparent... 

---