Semicrystalline thermoplastic appearances

The anisotropy of creep behaviour of oriented amorphous thermoplastics appears to have received even less attention than that of oriented semicrystalline thermoplastics. This may well be associated with the fact that early measurements based on standard tests demonstrated a marked... 

Aliphatic polyketones described here are a family of semicrystalline thermoplastics obtained by co- or terpolymerization of CO and ethene and/or higher a-olefins. Main emphasis will be on CO/ethene/propene-based terpol5uners [PK-EP]. These polymers can be produced with a wide range of compositions and molecular weights. Various aspects of polyketone catalysis, the pol5mierization process, the types and properties of polyketones, and their applications are reviewed. A number of reviews on polyketones have appeared in recent years (1-5). 

Fig. 5.71 Semicrystalline thermoplastics, such as a polyacetal, shown in polarized light (A) do not appear spherulitic after the addition of calcium carbonate (B). llie surface of such a filled, molded part can exWbit a matte finish due to poor wetting of the particles with the pol)nner. SEM observation of the molded surface (C) shows pock marks which are particles in cavities not filled with pol)nner. EDS mapping (D) shows the particles contain calcium.

The stress-strain curves of ductile thermoplastics (including both glassy amorphous polymers such as bisphenol-A polycarbonate and semicrystalline polymers such as polyethylene at room temperature) have the general shapes shown in Figure 11.16(a), which can be compared with the shape of the stress-strain curve of a very brittle material shown in Figure 11.16(b). The stress-strain curves of polymers which are neither very ductile nor very brittle under the testing conditions being utilized have appearances which are intermediate between these. two extremes. 

Unlike typical ethylene-based copolymers available in the polyethylene industry, which are semicrystalline materials, the ethylene norbornene copolymers are amorphous thermoplastic materials with a high heat distortion temperature of up to 170°C. They have a glossy, crystal clear appearance, with a high modulus (stiff material) and low shrinkage, which are important in the processability of the molten material. The high modulus of this copolymer is not unexpected. The polymer backbone due to the... 

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