Thermoplastics processing conditions

Table 3.6 Examples of unreinforced and reinforced thermoplastic processing conditions... 

The processing conditions of BAK poly(esteramide) are similar to those of pofyolefins [99], BAK 1095 resin can be processed into film and also into extruded or blow-moulded parts on conventional machinery used for processing thermoplastics. Processing conditions are given in Table 3.20. 

Processing affects the morphology of the blends and a wide range of morphologies are observed which depend on the ratio of LCP to thermoplastic, process conditions, temperature, shear rate, etc. 

Endres W, Lechner M D and Steinberger R (2003) The kinetics of the thermal decomposition of thermoplastic pol5Tirethane elastomers under thermoplastic processing conditions, Macromol Mater Eng 288 525-530. 

Thermosetting-encapsulation compounds, based on epoxy resins (qv) or, in some niche appHcations, organosiHcon polymers, are widely used to encase electronic devices. Polyurethanes, polyimides, and polyesters are used to encase modules and hybrids intended for use under low temperature, low humidity conditions. Modified polyimides have the advantages of thermal and moisture stabiHty, low coefficients of thermal expansion, and high material purity. Thermoplastics are rarely used for PEMs, because they are low in purity, requHe unacceptably high temperature and pressure processing conditions. 

The component with the lower viscosity tends to encapsulate the more viscous (or more elastic) component (207) during mixing, because this reduces the rate of energy dissipation. Thus the viscosities may be used to offset the effect of the proportions of the components to control which phase is continuous (2,209). Frequently, there is an intermediate situation where a cocontinuous or interpenetrating network of phases can be generated by careflil control of composition, microrheology, and processing conditions. Rubbery thermoplastic blends have been produced by this route (212). 

Most thermoplastic elastomers are stable materials and decompose only slowly under normal processing conditions. If decomposition does occur, the products are usuaHy not particularly ha2ardous and should not present a problem if good ventilation is provided. Extra caution should be exercised when processing polyurethanes, especiaHy those containing polycaprolactone segments. In these cases the decomposition products may include isocyanates and caprolactam, both of which are potential carcinogens. 

Because of its high stability, the processing window (range of processing conditions) is wider than for many other thermoplastics. The main points to bear in mind are ... 

An important subdivision within the thermoplastic group of materials is related to whether they have a crystalline (ordered) or an amorphous (random) structure. In practice, of course, it is not possible for a moulded plastic to have a completely crystalline structure due to the complex physical nature of the molecular chains (see Appendix A). Some plastics, such as polyethylene and nylon, can achieve a high degree of crystallinity but they are probably more accurately described as partially crystalline or semi-crystalline. Other plastics such as acrylic and polystyrene are always amorphous. The presence of crystallinity in those plastics capable of crystallising is very dependent on their thermal history and hence on the processing conditions used to produce the moulded article. In turn, the mechanical properties of the moulding are very sensitive to whether or not the plastic possesses crystallinity. 

The mechanism of droplet deformation can be briefly summarized as follows. The factors affecting the droplet deformation are the viscosity ratio, shear stress, interfacial tension, and droplet particle size. Although elasticity takes an important role for general thermoplastics droplet deformation behavior, it is not known yet how it affects the deformation of TLCP droplet and its relationship with the processing condition. Some of... 

The polymorphism can be inconvenient also for the processing, when small variations of the processing conditions can produce samples in different crystalline forms. This is, for instance, the case of s-PS, for which the crystalline form obtained by cooling from the melt (a and/or p) is dependent not only on the cooling rate but also on the crystalline form of the starting material, on the maximum temperature to which the melt is heated as well as on the time for which the melt is held at this maximum temperature (Sect. 3.1). This requires, in order to get reproducible manufacts, an extremely accurate control of the processing conditions, which is, of course, undesirable in thermoplastic materials. 

The degree of bonding analysis has been verified for both compression molding and online consolidation of thermoplastic composites. In these studies, composite test specimens were consolidated under controlled processing conditions. The most common types of tests performed to measure the interply bond strength were the interlaminar (short beam) shear test [21,25] or the lap shear test [12,21,26]. 

There are a number of general references available that contain detailed descriptions of the winding process and equipment itself [5,6], The purpose of this work, however, is to focus on the relationship between processing conditions and final part quality for both thermosetting and thermoplastic matrix filament wound cylinders. In the subsequent sections, an overview of the process will be presented, followed by detailed descriptions of current process modeling techniques and methods for determining cylinder quality. 

Consolidation/Fiber Motion Submodel The consolidation and fiber motion submodels evaluate the effects of processing conditions on the interaction between plies. In particular, the consolidation submodel (for thermoplastics) models the bonding between composite plies. The fiber motion submodel (for thermosets) yields the fiber position and fiber volume fraction within the cylinder. 

Processing. Polycarbonates may be fabricated by all conventional thermoplastic processing operations, of which injection molding is the most common. Recommended operating conditions are stock temperatures of 275—325°C and molding pressures of 69—138 MPa (10,000—20,000 psi). 

---