Mechanical Properties of Polycarbonate

As shown in Table 3.7, incorporation of 30% carbon fiber into polycarbonate more than doubles its tensile strength, with a useful increase in flexural modulus and severe loss of percent elongation. 

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S.C. Tjong and Y.Z. Meng, Effect of reactive compatibilizers on the mechanical properties of polycarbonate/poly(acrylonitrile-buta-diene-styrene) blends, Enr. Polym. J., 36(1) 123-129, January 2000. 

LeGrand, D.G. Mechanical properties of polycarbonates. In Handbook of Polycarbonate Science and Technology Plastics Engineering 2000 Vol. 56, 107-130. 

The most extensive studies of the dynamic-mechanical properties of polycarbonates have been reported by Yee et al. 

The use of PALF as reinforcement to improve mechanical properties of polycarbonate (PC) has been investigated [30]. The study focused on the tensile and flexural behaviours of PALF-polypropylene composites as a function of volume fraction. It follows that relatively soft polymeric surface of PC can easily scratch, and notch sensitivity at lower temperatures limits PC in some applications. The tensile modulus and tensile strength of the composites were found to be increasing with fibre content in accordance with the rule of mixtures. Fig. 23.5. 

In [25] the change in the molecular weight and mechanical properties of polycarbonate ("diflon" USSR) during oxidation under laboratory conditions, as well as under the conditions of casting reprocessing, was studied. 

Table 3. Mechanical Properties of Polycarbonate Derived from Cyclic Oligomers.

Polycarbonate is widely used in a nnmber of thermoplastic applications due to transparency and toughness. Copolymers of polycarbonate (PQ with polydimethyl siloxane (PDMS) fiirlher expand the property space to include extreme eonditions such as impact retention up to -60°C. It is known that hydrolysis of a carbonate linkage may lead to severance of polymer chains and may lead to deterioration of mechanical properties of polycarbonates under some conditions. Similarly for a molded part, physical aging at elevated temperatmes can also lead to deterioration of notched Izod impact of an amorphous polymer like polycarbonate . So, when a molded polycarbonate part is exposed to heat and humidity a combination of hydrolysis and physical aging may accelerate the property loss. Numerous approaches have been published in the past that leverage the use of various stabilizers to incrementally improve the performance. In this paper, we present the data for copolymers of polysiloxane with polycarbonate and their substantially improved heat aging and hydrolytic aging characteristics. 

Structure and Crystallinity. The mechanical—optical properties of polycarbonates are those common to amorphous polymers. The polymer may be crystallized to some degree by prolonged heating at elevated temperature (8 d at 180°C) (16), or by immersion ia acetone (qv). Powdered amorphous powder appears to dissolve partially ia acetone, initially becoming sticky, then hardening and becoming much less soluble as it crystallizes. Enhanced crystallization of polycarbonate can also be caused by the presence of sodium phenoxide end groups (17). 

Table 20.3 Comparison of mechanical properties of typical commercial bis-phenol A polycarbonates...

The most desirable property of polycarbonates is their high ductility on impact, relative to other engineering polymers in the unmodified state. There is no consensus on the mechanism of ductility researchers continue to explore this behavior through molecular dynamics studies of chain segment motion during the formation of crazes and propagation of the failure. 

In the early literature it is suggested that polycarbonates can be easily plasticized with common plasticizers. Plasticization of polycarbonate has been investigated by Kozlov et al. (12). These authors described the influence of plasticization on softening points and mechanical properties of bisphenol A polycarbonates. They conclude that the behavior of plasticized polycarbonate is similar to that encountered for most amorphous polymers. The influence of crystallization effects promoted by the plasticizer was not taken into account. 

The mechanical properties of poly(methyl methacrylate), PMMA, have been studied for quite a long time and, in addition to its industrial interest, PMMA constitutes a kind of reference material. Indeed, among the amorphous linear polymers it represents an intermediate between the very brittle polystyrene and the tough bisphenol A polycarbonate considered in Sect. 4. Furthermore, as shown in [1] (Sect. 8.1), the molecular motions responsible for its large p transition are precisely identified, as well as the nature of the cooperativity that develops in the high temperature range of the p transition. 

Investigation of the mechanical properties of bisphenol A polycarbonate (BPA-PC) and tetramethyl bisphenol A polycarbonate (TMBPA-PC) has led to... 

The co-injection moulding of PVC-U with other thermoplastics (glass fibre reinforced PVC, polypropylene, ABS and polycarbonate), was investigated using the mono-sandwich process and the properties determined. Polypropylene was the only polymer not to exhibit good adhesion. The mechanical properties of the other samples were intermediate between those of the constituent polymers (104). 

Weld lines (also known as knit lines) are a potential source of weakness in molded and extruded plastic products. These occur when separate polymer melt flows meet and weld more or less into each other. Knit lines arise from flows around barriers, as in double or multigating and use of inserts in injection molding. The primary source of weld lines in extrusion is flow around spiders (multiarmed devices that hold the extrusion die). The melt temperature and melt elasticity (which is mentioned in the next section of this chapter) have major influences on the mechanical properties of weld lines. The tensile and impact strength of plastics that fail without appreciable yielding may be reduced considerably by in doublegated moldings, compared to that of samples without weld lines. Polystryrene and SAN copolymers are typical of such materials. The effects of weld lines is relatively minor with ductile amorphous plastics like ABS and polycarbonate and with semicrystalline polymers such as polyoxymethylene. Tliis is because these materials can reduce stress concentrations by yielding [22]. 

The mechanical properties of a craze were first investigated by Kambour who measured the stress-strain curves of crazes in polycarbonate (Lexan, M = 35000) which had first been grown across the whole cross-section of the specimen in a liquid environment and subsequently dried. Figure 25 gives examples of the stress-strain curves of the craze determined after the 1st and 5th tensile loading cycle and in comparison the tensile behavior of the normal polymer. The craze becomes more and more elastic in character with increasing load cycles and its behavior has been characterized as similar to that of an opencell polymer foam. When completely elastic behavior is observed the apparent craze modulus is 25 % that of the normal poly-... 

As could be expected, the mechanical properties of a crazed polymer differ from those of the bulk polymer. A craze containing even 50% microcavities can still withstand loads because fibrils, which are oriented in the direction of the load, can bear stress. Some experiments with crazed polymers such as polycarbonate were carried out to get the stress-strain curves of the craze matter. To achieve this aim, the polymer samples were previously exposed to ethanol. The results are shown in Figure 14.24 where the cyclic stress-strain behavior of bulk polycarbonate is also illustrated (32). It can be seen that the modulus of the crazed polymer is similar to that of the bulk polymer, but yielding of the craze occurs at a relatively low stress and is followed by strain hardening. From the loading and unloading curves, larger hysteresis loops are obtained for the crazed polymer than for the bulk polymer. 

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