Drying, injection moulding

Polynorbomene is also of interest to the plastics processor since by using a dry blending process for mixing and a modified injection moulding process for fabricating, the use of conventional rubber-processing equipment may be avoided. 

The dried beads may be supplied as injection moulding material without further treatment or they may be compounded with additives and granulated. 

Dried granules may be injection moulded, blow moulded and extruded without undue difficulty with melt temperatures of 220-260°C. The moulding shrinkage (0.003-0.004 cm/cm) is very low and a somewhat greater than normal draft may be required in deep draw moulds. 

Table 2,1 provides some information on the two polymers that are supposed to be free of chemical crosslinks. Phenoxy PKHJ is a product of Union Carbide Corporation. Plates were produced by injection moulding after drying of the granulate. On the other hand, polymer E was prepared by casting as were the other experimental polymers but without adding PGCBA to the mixture. 

In this paper, all the blends and composites are designated by the type of matrix (G for the neat nylon, D for the 8 wt % rubber-modified nylon and N for the 20 wt % rubber-modified nylon), the concentration of fibres and the type of fibre/matrix interface (A or B). As an example, a material designed DlOB is a ternary blend made of DZ matrix and 10 wt% of type B fibres. After drying the specimens for 24 hours at 100°C, they were stored in plastic bags inside a desiccator. In comparison with freshly injection moulded samples, the moisture content in the specimens ready for mechanical testing is about 2 wt%. All the mechanical tests were conducted in an environmental chamber in controlled conditions a temperature of 20°C under a continuous argon flow. 

Figure 7.6. Microhardness of injection moulded PET, measured at the outer surface, as a function of mould temperature. The injection was performed using conventional samples as received (A) dried samples ( ). (From Balta Calleja et al., 1993.)...

It is known (Friedrich Fakirov, 1985) that injection moulding of PET which has not been carefully dried results in a serious degradation of its mechanical properties profile due to hydrolitic degradation of the molecular weight, leading to an increase... 

In the above studies compression and injection moulding were carried out with native potato starch dried at room temperature and then mixed with 7% water. After processing, the samples were subjected to ambient atmosphere and investigated after a storage time of at least 4 weeks. 

Samples were then injection moulded into tensile testing bars at 245°C. Before processing, all samples were dried in an oven for at least 24 hours at 65°C. 

The finished dry rubber and latex based rubber products can be vulcanized by several techniques depending on the type of rubber compound (dry rubber compound/latex compound), size of the finished product, and its shape and structure. Moulded rubber products are vulcanized by press curing using compression, transfer, or injection moulding presses. The vulcanization techniques other than moulding may be grouped into batch and continuous methods. The batch methods include the use of autoclaves, hot air/gas oven, and hot liquid/ water bath. Rubber products may be vulcanized at room temperature by cold curing either by immersion of rubber products in a carbon disulphide solution of sulphur chloride (SjCy, or by exposure to its vapour. 

Cellulose acetate is the most important cellulose ester and various processing techniques for forming shaped bodies exist for this polymer. The mixed esters discussed above, CAP and CAB, are used predominantly for injection moulding applications in suitably plasticized form and are marketed as pellets. This is done for CA as well, but additionally, alternative processing routes are available where solution methods play an important role. This is in particular the case for fibre spinning and (thinner) film manufacture where cellulose diacetate (CDA) is dissolved in acetone and dry spun or solvent cast. Moreover, the traditional solventusing block process is employed for obtaining sophisticated, multicoloured thick sheets for applications like spectacle frames. 

For blow and injection moulding, as well as extrusion, pellets are produced prior to the final shaping of the desired body. The CDA powder is mixed in a dry blender with plasticizer (essentially phthalic esters) and other additives such as colorants and the mixture is aged or matured at 60 to 80 °C for a few hours to allow for diffusion of the plasticizer. Subsequently,... 

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