Incorporation of Glass Fibers

The melt cools down when glass fibers are added. It is therefore necessary that the melt temperature is sufficiently high before adding the fibers to ensure that the polymers do not cool down to their solidification temperature. Too great an increase in viscosity caused by cooling will prevent the melt from wetting the fibers, in which case the melt will cause mechanical stress and damage to the fibers. The size reduction of the fibers depends on the 

To prevent significant reduction of the fiber length, the lowest possible screw speed and/or the highest possible throughput and degree of filling should be selected. However, the opposite process parameters are required to ensure effective distribution of the fibers (see Section 4.2.4). Therefore, glass fiber incorporation is an optimization process. 

After wetting, dispersion, and pre-comminution of the fibers, the melt is devolatilized to achieve a perfect pumping and constant material flow within the die. Comminution must be completed prior to the devolatilization zone to prevent fibers from being separated and deposited in the devolatilization area. 

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The increase in stiffness of an unsaturated polyester resin by incorporation of glass fibers can be demonstrated by the following small-scale experiment two small dishes of equal size (10 x 10 x 3 cm) are formed from aluminum foil. Subsequently, 0.2 g of dibenzoyl peroxide are mixed into 20 g of an unsaturated polyester in styrene (see Ex-... 

Some interesting differences are noted between amorphous and crystalline polymers when glass fiber reinforcement is incorporated into the polymer. In Figure 1.44, it will be seen that incorporation of glass fiber has a minimal effect on the... 

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. 

Such enhancements in tensile properties by the incorporation of glass fiber into the polymers have been important in the introduction of plastics into engineering applications. 

As seen in Table 3.4, in general the incorporation of glass fiber into polymer formulations, not unexpectantly, leads to a large reduction in elongation at break. 

As shown in Table 3.5, the incorporation of glass fibers causes little or no change in Izod impact strength. 

The incorporation of glass fiber info polyamide 6 increases the tensile strength from 40 to 145 GPa (Table 3.1), accompanied by an increase in flexural modulus (Table 3.2) from 1.0 to 1.6 MPa and hardly any change in elongation at break (Table 3.4). 

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 glass fiber decreases wear resistance but improves the coefficient of friction of this polymer. 

Li et al. [51] investigated the effect on volume resistivity brought about by the incorporation of glass fibers into polypropylene-epoxy resin composites. 

Volume resistivity and dielectric strengths are virtually unaffected by the incorporation of glass fiber, while the dielectric constant undergoes a moderate increase. 

Such considerations must be borne in mind when it is necessary to improve the physical properties of plastics, whether or not they have been reinforced by the addition of various agents. For example, a plastic that has been reinforced by the incorporation of glass fiber suffers a deterioration in physical properties. The greater the exposure, the greater is the loss in these properties. 

Virtually every thermoplastic material will receive some benefits from the incorporation of glass-fiber reinforcements. However, the improvements are more dramatic for some polymers than others (see Table 8-1). 

For the incorporation of glass fibers, these are processed as roving and then cut at the necessary dimensions. This operation is done before feeding into the extruder or directly by the screw of the extruder. 

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