Glass polyester creep

Figure 4.15 Creep curves for UD glass polyester in bending (reference 4.62).

High strength Stiffness at elevated temperatures Mineral reinforced Most economical Low warpagc Polyester (glass reinforced) High stiffness Lowest creep Excellent electrical properties properties... 

The workhorse of the RTS industry is TS polyester (also called polyester-TS) with glass fiber. The fiber reinforcement may be in the form of chopped fibers, porous nonwoven mats, woven fabrics, or continuous fibers. The combination of plastics and reinforcements results in versatile materials with unusual characteristics. The reinforcement adds strength and toughness to inherent weather resistance, moldability, and colorability. Thus RTSs are used because of their increased tensile, flexural, torsional, and impact strengths increased modulus of elasticity increased creep resistance reduced coefficient of thermal expansion increased thermal conductivity and, in many cases, lower costs. 

Polyolefin fibers, on the other hand, have some drawbacks when compared to common textile fibers such as polyester. These limitations include relatively lower resiliency, creeping due to their low glass transition temperature (Tg), poor... 

Most of the high-volume automotive polymers arc thermoplastics the common virtues of polypropylene, ABS (acrylonitrile butadiene styrene), PVC (polyvinyl chloride), nylon, polyethylene and polycarbonate etc., are their versatility, ability to be injection moulded or extruded into intricate shapes, and suitability for mass production. Thermosets used in significant volume include phenolics, long used as electrical components, and now finding application in non-burning creep-resistant underbonnet items, and glass-reinforced polyesters, used originally in hand lay-up processes, but nowadays widely used in SMC. 

Figure 3-54. An example of tensile creep curves in the direction of maximum fiber orientation, a) A TS polyester RP having 56 percent E-glass, by weight b) glass-fabric/TS polyester RP in 48 percent glass by weight.

Fig. 3-20 compares the flexural modulus versus temperatures for four 30% GRTP s. Because modulus is a frequently appearing property in mechanical design equations, creep data often are plotted as apparent or creep modulus. These data are shown in Table 3-6 for GRTP s. As can be seen, the apparent creep modulus improves with glass reinforcement. Generally, the creep modulus of the reinforced thermoplastics decreases as stress and temperature are increased. However, the creep modulus data for reinforced nylon, acetal, polyester, polysulfone, and polyvinyl chloride appear to be less dependent on stress under the conditions of this particular test. When creep modulus data at different stresses coincide—a phenomenon known as the Boltzman superposition—there is an obvious reduction in the amount of testing required. However, such a relationship is both temperature and stress dependent and must be confirmed at the conditions of interest for the specific material involved. Other techniques, such as time-temperature superposition and other empirical correlations, also have been devised to simplify the time-dependent response of plastics ... 

Figure 3-12. Flexural Creep of 15% TFE, 30% Glass-Reinforced Polycarbonate, Nylon 6, and Thermoplastic Polyester Resins at 73° F, 2000 psi in Air ...

The low density of these fibres - about 0.97 g cm - means that in terms of specific stress and specific modulus (i.e. on a mass per unit length basis) they rank very highly. However, they are limited in composites by their low melting temperatures (about 140°C), tendency to creep, and the need for special surface-activation processes, such as corona discharge treatment, to develop adhesion to matrix polymers. They are sometimes used alone, but more often in hybrid yam and fabric stmctures with glass or carbon fibres in an epoxy or unsaturated polyester resin matrix to improve the impact resistance and energy absorption. Curing temperatures should not exceed 125°C. 

Starch is one of the most widely used biopolymer in biocomposites because of its low cost and versatility. A plasticizer like glycol is sometimes used to make it suitable for processing. It is also blended with other polymers like aliphatic polyesters to improve its physical and mechanical properties. Biocomposites based on starch matrices show improved properties, which are comparable to E-glass/epoxy composites. Tensile, flexural, impact, and creep properties of these biocomposites are significantly better than those of neat starch. Various biofiber surface treatments have been shown to improve the properties of starch-based biocomposites. 

---