Polypropylene Thermal expansion coefficient

Figure 2.27 shows both the V-T and a-T curves. It can be seen that at Tg there is a discontinuous change in the thermal expansion coefficient. Thus, for atactic polypropylene Tg = — 19°C), the thermal expansion coefficient a for the glass (just below Tg) is 2.2 x and for the liquid it is... 

A special case of interest is reinforced polypropylene with various fibers. Often transcrystallinity in polypropylene occurs which is due to dense heterogeneous nucleation by a substrate. The occurrence of transcrystallinity depends on the type of fiber and the temperature. In contrast to transcrystallinity in quiescent crystallization, the application of stress at the interface between a fiber and a PP melt results in the crystallization of polypropylene on a row-nuclei around a fiber. This effect is caused by strain-induced nucleation via some self-nucleation mechanism and is independent of the type of fiber and less dependent on the temperature of crystallization [5,6]. Axial stress arises also during cooling of two materials with a large difference in thermal expansion coefficients. As such, the stress-induced nucleation in reinforced PP depends also on the cooling rate, fiber length, position along the fiber and viscoelastic properties of the PP melt [5]. 

In injection molding, the pol5uner is cooled from the melt temperature to a temperature below the solidification, which is accompanied by a reduction of pressure in a mold before the molded item is ejected from the mold. Since the ejected molded part is still hot, its cooling to room temperature occurs under atmospheric pressure. As a result of temperature and pressure changes, the cooled polymer shrinks according to the PVT (pressure-specific volume-temperature) relationship or the thermal expansion coefficient of the polymer. The linear mold shrinkage is 0.1-0.8% for amorphous polymers and 1.0-2.0% for crystalline polymers. For polypropylene, it is about 1.7%. Shrinkage affects the dimensional accuracy and dimensional stability of molded items. 

Polymers generally have high thermal expansion coefficients and the addition of aligned graphene nanoplatelets to polypropylene has been shown to reduce the thermal expansion coefficient in two directions rather than one in the case of aligned fibres.A similar reduction in the thermal expansion coefficient of an epoxy resin is obtained with the use of graphene oxide. It is also found that the addition of graphene-based nanofillers to a polymer can... 

There are standard procedures for determining aj (e.g. ASTM 696) and typical values for plastics are given in Table 1.2. It may be observed that the coefficients of thermal expansion for plastics are higher than those for metals. Thus if 50 mm lengths of polypropylene and stainless steel are each heated up by 60°C the changes in length would be... 

A rod of polypropylene, 10 mm in diameter, is clamped between two rigid fixed supports so that there is no stress in the rod at 20°C. If the assembly is then heated quickly to 60°C estimate the initial force on the supports and the force after 1 year. The tensile creep curves should be used and the effect of temperature may be allowed for by making a 56% shift in the creep curves at short times and a 40% shift at long times. The coefficient of thermal expansion for polypropylene is 1.35 x 10 °C in this temperature range. 

When a pipe fitting is tightened up to a 12 mm diameter polypropylene pipe at 20°C the diameter of the pipe is reduced by 0.05 mm. Calculate the stress in the wall of the pipe after 1 year and if the inside diameter of the pipe is 9 mm, comment on whether or not you would expect the pipe to leak after this time. State the minimum temperature at which the fitting could be used. Use the tensile creep curves and take the coefficient of thermal expansion of the polypropylene to be 9.0 X 10- °C . 

Thermal expansion-contraction of plastics will be considered in detail in Chapter 10, Temperature-driven expansion-contraction of wood-plastic composites. Linear coefficient of thermal expansion-contraction. Here it can be briefly mentioned that this property is about the same with HDPE, polypropylene, PVC, ABS, and Nylons 6 and 6/6, and the respective coefficients of thermal expansion are all overlapping in the range of 2-7 X 10 1/°F (4-13 X 10 1/°C). Only with LDPE the coefficient is noticeably higher and equal to 6-12 X 10 1/°F (10-22 1/°C) [12]. 

TABLE 10.10 The linear coefficient of thermal expansion-contraction for HDPE-based WPC. The published article [4] did not provide details on the formulation of the composite material. MAPP — maleic anhydride derivative of polypropylene (see Chapter 5). 

A straight section of polypropylene pipe is fixed rigidfy at its ends. Its tensile stress relaxation modulus at time t and coefficient of linear thermal expansion at 20°C are, respective. ... 

The addition of talc to polypropylene reduces the coefficient of thermal expansion by about 50%, in the temperature range from 50 to 150°C at 30% loading 6 x 10 in/in/°C for impact copolymer resin versus 3 X 10" in/in/X with a 30 wt% loading of talc. The effect appears to be independent of the fineness of grind of the talc. 

The papers read showed that, for application at low temperatures down to 4 K, the most critical properties of nonmetallic materials are their flexibility and resultant mechanical behavior, their coefficients of thermal expansion as compared with that of the inorganic materials with which they are combined, and their thermal conductivity. At present, the leading pol3nneric materials for low-temperature applications are epoxy resins, polypropylene, and polyimide strips and films, and polystyrene and polyurethane based foams. The leading fibers for reinforcement are glass, graphite, boron, and organic polyaramid. 

Table 3.3-6 Polypropylene, PP heat capacity, thermal conductivity, and coefficient of thermal expansion...

Of the GRTP only ABS, polypropylene, poly-sulfone, and modified phenylene oxide are electroplated. Of these ABS represents about 85% of the market. Since the introduction of platable plastics, new formulations have been developed to give superior physical properties, platability, and appearance. For example, 25% glass-filled ABS has a shrinkage nearly equal to that of die-cast metals the increased stiffness reduces distortion during the plating operation and a reduction of 50% in the coefficient of linear thermal expansion permits it to pass the standard thermal cycling test of 82 to -40 C (190 to - 40 F) (Ref. 29). 

Lusenac America offers a broad line of talc products for use In polypropylene homopolymer. Talc increases the stiffness and heat distortion temperature (HOT) of polypropylene. It also reduces the coefficient of thermal expansion. Typical talc loadings are 20 to 40%. Because homopolymers do not have good impact strength, the talc products recoaunended are relatively coarse and vary based on price, talc content, color and longterm heat aging (LTHA). 

Zhang X, Hillenbrand J, Sessler GM (2004) Piezoelectric 33 coefficient of cellular polypropylene subjected to expansion by pressure treatment. Appl Phys Lett 85 1226 1228 Zhang X, Hillenbrand J, Sessler GM (2006) Thermally stable fluorocarbon ferroeleetrets with high piezoelectric coefficient Appl Phys A Mater Sci Process 84 139 142... 

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