Unreinforced polymer

Strength numbers are ratios of properties of reinforced polymer to unreinforced polymer. 

Many unreinforced polymers (especially amorphous ones) are susceptible to crack propagation under impact or tensile loading. They are vulnerable... 

The highest temperature at which an unreinforced polymer can safely be used for short and intermediate time periods is often determined by physi-... 

Polymers Unreinforced polymer Glass fibre reinforced polymer ... 

Data on virgin unreinforced polymer in parenthesis. Source Author s own files ... 

Weld Lines. In unreinforced polymers, smooth fracture surfaces may be a sign of weld-line failure (Fig. 13a). This is a case of adhesive failure the melt fronts were imable to join together in such a way that cohesive failure and the corresponding deformation in the fracture surface or different fracture planes, shown in Figure 13b, could occur. 

For most thermoforming operations using unfilled or unreinforced polymers, the differential pressure is less than 0.5-1.0 MPa (145 psi). Differential pressures of more than 3.0 MPa may be needed for high performance reinforced polymers. 

The following standardized and non-standardized methods are used to measure the properties and stmctuies of reinforced and unreinforced polymers and polymer composites ... 

The layered structure of fiber composites made exclusively of polypropylene enables numerous attractive and balanced properties, which are not attainable for unreinforced polymers or conventional fiber composites [72],... 

Some of the important mechanical properties used to evaluate unreinforced polymers are listed in Table 2.1 for a range of virgin plastics. These methods can also be used to evaluate reinforced plastics, as will be seen later. 

Dynamic mechanical analysis measures changes in mechanical behavior, such as modulus and damping as a function of temperature, time, frequency, stress, or combinations of these parameters. The technique also measures the modulus (stiffness) and damping (energy dissipation) properties of materials as they are deformed under periodic stress. Such measurements provide quantitative and qualitative information about the performance of materials. The technique can be used to evaluate reinforced and unreinforced polymers, elastomers, viscous thermoset liquids, composite coating and adhesives, and materials that exhibit time, frequency, and temperature effects or mechanical properties because of their viscoelastic behavior. 

Particular applications of the techniques in studies of the viscoelastic and rheological properties of unreinforced polymers are reviewed in Table 2.7. 

Measurement of Rheological and Viscoelastic Properties of Unreinforced Polymers... 

It is seen in Table 3.1 that polyamide 6 improves its tensile strength from a value of 40 MPa to 145 MPa, that is, by a factor of about 3.6. The improvement obtained by the incorporation of glass fiber into polybutylene terephthalate was even more dramatic, from 52 to 80-196 MPa. Very useful improvements in tensile strength result from the incorporation of glass fiber into the formulation. Such improvements ranged from 17 to 41 MPa on unreinforced polymer to 180 MPa on glass-reinforced polytetrafluoroethylene. 

The incorporation of 30% of glass fiber into polyphenylene oxide brings about a relatively small increase in tensile strength from between 50 and 65 MPa for the unreinforced polymer to 85 MPa in the reinforced polymer (Table 3.1). The addition of glass fiber is accompanied by an increase in flexural modulus from 2.5 to 17.2 GPa (Table 3.2) and a dramatic decrease in modulus of elasticity from between 20 and 60% down to 1% (Table 3.4). The incorporation of glass fibers into polyphenylene oxide produces a distinct improvement in the wear resistance of the reinforced polymer accompanied by small improvements in fatigue index [19] and the coefficient of friction [20]. 

The incorporation of silica into epoxy resins has little effect on tensile strength. The tensile strength of reinforced epoxy resin is 30-84 MPa, compared to values of 68-72 MPa for silica-reinforced polymer. The flexnral modulus falls from 80 GPa for the unreinforced polymer to 15 GPa for the reinforced polymerm while elongation at break remains virtually unchanged. 

Dielectric constant data have been reported on several unreinforced polymers, including polyimides [19-21], silicones [22], epoxy resins [23], polyurethanes [23], polyaniline nanofibers [16, 17], zirconium nanocomposites [24], cross-linked polyethylene [15], low-density polyethylene [22], doped polyimines [19], polyimide-3-zirconium propoxide nanocomposites [24], poly linu-naphthyl ether [30], and cross-linked polyethylene-polyethylene polyacrylate acid blends [15]. 

A discussion now follows on the effect of various types of radiation on the retention of physical properties in reinforced and unreinforced polymers. We will start with a discussion of the effects of gamma radiation. 

The same materials can be used as in long-fibre reinforced polymer matrix composites. Short-fibre reinforced polymers are useful in many applications where unreinforced polymers are not sufficient. The design of injection moulded components made of short-fibre reinforced polymers is complicated by the fact that the orientation of the fibre is determined by the fluid flow (see section 9.1.1) and can be irregular within the material. 

This discussion of DTUL in relation to resin properties does not explain why crystalline materials respond so well. It has been suggested that the type of crystallinity in the reinforced system, not the percentage crystallinity, is different in the unreinforced polymer. It is also recognized that the reinforcement must be glass fiber to get maximum performance. ... 

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