Flow during processing

Many modifiers and additives have been described for use with nylon composites, but generally a small amount, 0.05—1 wt %, of a lubricity aid, such as sodium or 2inc stearate (4) is added to enhance both resin flow during processing and removal from the mold after consoHdation. 

In these systems, emulsifiers can be used to disperse oily ingredients such as flavours. Another use is to make it easier for the granules to flow during processing. 

Polymers have long-chain molecules whose entanglement tends to be unravelled with orientation in the direction of flow during processing. 

Additives are used for a wide variety of purposes, and may be classified as fillers, anti-oxidants, stabilisers, plasticisers, fire retardants, pigments and lubricants. Anti-oxidants and stabilisers are usually used in rather small quantities in order to prevent degradation of the polymer when it is exposed to air, light and heat the intention here is to maintain the properties of the polymer rather than to modify them. Fillers may be used either simply to produce a cheaper product or to improve the properties, in particular the mechanical properties. Lubricants may be used externally, to prevent adhesion of the polymer to the processing equipment, or internally, either to aid flow during processing or to reduce friction between the product and other materials. 

FIGURE 41.6. Elastic modulus at 25 °C of PET/xPHB copolymers as a function of x in the direction parallel to the flow during processing after [50]. 

Processability. Plasticizers are often used to increase melt flow during processing, particularly in rubber, ceUulosic plastics, and coatings. In vinyl plastisol technology, powdered resin is slurried in nonsolvent plasticizer at room temperature for easy processing in low-cost equipment and then heated to dissolve and cooled to gel into the final product. 

C, respectively). Therefore, we expect them to have the advantage that their polymer blend can maintain high temperature properties. The polymer blend of PA4,6/PPS has been used industrially without any compatibilizers nevertheless, the blend is immiscible. Thus, it is considered that the shear flow during processing plays an important role for the formation of the phase-separated morphology related to the appearance of desirable properties. 

In the early 1960 s we also became interested in the relationship between flow during processing and the kinetics of crystallization. Preliminary studies of crystallization of quiescent melts were undertaken from the point of view of that used by metallurgists. 

These thermotropic liquid-crystalhne polymers have high melting points but can be melt-processed like other thermoplastics. The macroscopic orientation of the extended-chain crystals depends on the orientation imparted by flow during processing (molding, extrusion, etc.). Because of the fibrous nature of the extended-chain crystals, these plastics behave as self-reinforced composites, with excellent mechanical properties, at least in the chain direction. This is illustrated in Table 4.3 for molded specimens of a hquid-crystalline copolyester of ethylene glycol, terephthalic acid, and / -hydroxybenzoic acid [14]. In the direction parallel to the flow, the properties listed in Table 4.3 favorably compare with ordinary crystalline thermoplastics (nylons, polyesters) reinforced with up to 30% glass fibers. 

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