Polyester composites impact strength

By way of conclusion, the SIN materials were quite different from the original sequential IPN compositions. While the polyester linkage could be used with the sequential mode of synthesis also, its presence in the SIN made for much better impact strengths, probably because of the lower elastomer Tg permitted. The SIN synthesis allowed a greater range of compositions to be made. 

A typical unsaturated unreinforced polyester resin has an extremely low notched Izod impact strength. The addition of fibrous glass can change this extremely brittle material into a high impact strength composite. The same phenomenon occurs with some brittle thermoplastics, such as polystyrene and styrene—acrylonitrile. 

The most successful application of the RIM-process is in the production of polyurethane-based materials. Other systems, such as composites based on polycaproamide, epoxy resins, and unsaturated polyesters can also be processed by reactive injection molding. New reactive systems have also been specially created for the RIM-process260 because of the exceptional opportunities it offers for manufacture of finished articles from engineering plastics with a high modulus of elasticity and impact strength. The automotive industry, which is the main customer for RIM-articles, can utilize this technology to manufacture of massive parts such as body panels, covers, wings, bumpers and other made of newly developed plastics. 

A flexibilized thermohardening composition contained ca. 90% BPA/DC and a polyester from dimerized fatty acids and hexanediol. Elongation at break and impact strength increased considerably, whereas the heat deflection temperature was only little decreased [139],... 

PolyeCL has an ability to blend with several other polymers and can be used as an adhesive for polymer films of the same or different composition, as an excellent low-profile additive for fiber-glass-reinforced polyesters and as a pigment dispersant. It improves the impact strength and crack resistance of some thermoplastic polymers. 

Although it might be expected that a combination of brittle reinforcing fibers and a brittle matrix (e.g., epoxy or polyester resins) would have low impact strength, this is not the case, and the impact strengths of the fibers or the matrix. For example, polyester composites with chopped-strand mat have impact strengths from 45 to 70 ft-lbf/in (94-147 kj/m ), whereas a typical impact strength for polyster resin is only about 1 ft-lbf/in (2.1 kj/m ). 

PBT is a semiciystaUine, white or off-white polyester similar in both composition and properties to PET. It has somewhat lower strength and stiffness than PET, is a little softer but has higher impact strength and similar chemical resistance. As it crystallizes more rapidly than PET, it tends to be preferred for industrial scale molding. Its structure is shown in Figure 4.28. 

Mishra et al. [36, 37] tested the tensile and impact strength of maleic anhydride-treated sisal composite at different fiber volumes and found that tensile and impact strength decreased gradually from 40% fiber volume composite to 55% fiber volume polyester composite. It was concluded that maleic anhydride-treated composite at fiber volume 40% showed higher and better mechanical properties [36, 37]. Related to tensile properties evaluation, Mishra et al. [36, 37] concluded that a composite of alkali treated (5%) sisal fiber was fotmd to achieve better mechanical properties as compared to rmtreated, dewaxed, 10% alkali treated and bleached sisal fiber-reinforced composites. A 5% alkali-treated sisal fiber-reinforced composite... 

---