Initiator Injection moulding

The steps in the process are illustrated in Fig. 4.48. Initially a preform is injection moulded. This is subsequently inflated in a blow mould in order to produce the bottle shape. In most cases the second stage inflation step occurs immediately after the injection moulding step but in some cases the preforms are removed from the injection moulding machine and subsequently re-heated for inflation. 

The surface finish of injection-moulded foamed articles are not ideal because of external defects, burst bubbles, etc. This can be avoided by sandwich moulding. This is accomplished by initially injecting a slug of polymer melt into the mould followed immediately by a polymer containing a blowing agent, which chases the initial polymer into all the interstices. 

Isothermal and dynamic DSC were demonstrated to be useful tools for following the oxidative stability as a function of repeated injection moulding of glass fibre reinforced nylon [121]. Similarly DSC and OIT showed that a common feature for PP and HDPE is that the OIT sharply decreases after the two first extrusion steps due to the large amount of antioxidant initially con-... 

Figure 7.10 shows the microhardnesses of several injection moulded starch samples processed at different temperatures with different initial water content. There is an increase in H with the injection moulding temperature in the range 80-110 °C, from 120 MPa to 140 MPa (Balta Calleja etal, 1999). These microhardness values are notably higher than those found for conventional injection moulded thermoplastic polymers like PE (50-60 MPa) (Rueda et al 1989 Balt Calleja et al., 1995). 

The cure effects on the chemoviscosity are two-fold the viscosity will initially decrease due to the increase in thermal effects but will eventually increase due to formation of the crosslinked network via the curing reaction. This is shown schematically for the chemoviscosity of a polyester resin during injection moulding in Figure 4.8. 

The investigated injection moulded samples showed initially mostly homogeneous WAXS p>attem with Debye-Scherrer patterns related to the reflexes mentioned in table 1. The samples are to a large extent crystallised. Heating the samples to about 110 °C didn t change the WAXS pattern. 

At present, PLA-based materials are mainly referenced on three different markets, namely, the biomedical (initial market), the textile (mainly in Japan) and the packaging (mainly food, i.e. short-term applications). For instance, reported types of manufactured products are blow-moulded bottles, injection-moulded cups, spoons and forks, ther-moformed cups and trays, paper coatings, fibres for textile industry or sutures, films and various moulded articles [8]. 

RIM is a relatively new process. It can be used for processing of unfilled resin as well as fibre-reinforced composites. The process was discussed in Chapter 1. The process is similar to RTM (discussed previously) with some variation in mould release and reinforcement sizing to optimise resin chemistry with the process. The low viscosity reactant systems facilitate composite materials production, so-called structural RIM composites [19, 20] in which continuous fibre reinforcement mats are placed in mould cavities before injection. Capital investment and operational cost in RIM are therefore much less than those for conventional injection moulding. Polymerisation of a monomer is usually initiated by heat. However, in RIM, the polymerisation is initiated by impingement mixing (not by heat). Hence it is possible to activate polymerisation at relatively low temperature. Unlike RTM, in RIM the mould-fill times are very low ( 1 s) and a cycle time of <60 s is typical. The process is used for the rapid and automated production of large, thin and complex-shaped parts. 

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