Polymer, thermal property heat dissipation

T and are the glass-transition temperatures in K of the homopolymers and are the weight fractions of the comonomers (49). Because the glass-transition temperature is directly related to many other material properties, changes in T by copolymerization cause changes in other properties too. Polymer properties that depend on the glass-transition temperature include physical state, rate of thermal expansion, thermal properties, torsional modulus, refractive index, dissipation factor, brittle impact resistance, flow and heat distortion properties, and minimum film-forming temperature of polymer latex... 

General-purpose polymers, being thermal insulators, cannot dissipate heat generated by mechanical work or by electronic devices and so on. If the temperature rises, the mechanical properties of the polymer decrease and ageing speeds up. Eventually, the temperature can reach the melting point. 

Polymers have unique properties important for processing, viz., low thermal diffusivity, high viscosity and viscoelasticity. Because of the low thermal conductivity, efficient plastication cannot be based on thermal diffusivity alone. Polymer melting requires generating heat dissipation through intensive deformation of the highly viscous melts, leading to thin films. 

The following table shows some thermal properties of three thermoplastic polymers. Compute the screw output for each polymer material if the screw drive power input is 60 hp and the mechanical efficiency is 75%. Assume that the heat requirement for molding the materials is satisfied by the viscous dissipation... 

Composites usually consist of a reinforcing material embedded in various matrices (binder). The elfective method to increase the strength and to improve the overall properties of composites is to incorporate dispersed phases into the matrix which can be an either polymer or engineering materials such as ceramics or metals. Hence, metal matrix composites (MMCs), ceramic matrix composites (CMCs) and polymer matrix composites (PMCs) are obtained. Besides, hybrid composites, metal/ceramic/polymer composites and carbon matrix composites can also be obtained. MMC and CMC composites are developed to withstand high temperature applications. MMCs are also used in heat dissipation/electronic transmission applications due to the conductive nature of metals (electrically and thermally). 

The thermal characteristics of NR-metal composites are close to the properties of metals, whereas the mechanical properties and the processing methods are typical of polymers.Thermally conducting, but electrically insulating, polymer-matrix composites are increasingly important for electronic packaging because the heat dissipation ability limits the reliability, performance and miniaturization of electronics.Thermal properties such as thermal conductivity, thermal dilfusivity and specific heat of metal (copper, zinc, Fe and bronze) powder-filled polymer composites are investigated experimentally in the range of filler content 0-24% by volume. ... 

Natural fibre-reinforced polymer composites are considered as replacement for metals or carbons in situations where they have better mechanical properties. But the thermal properties of these composites are in general much lower than that of metals. Consequently, it is more difficult to dissipate the heat, and in some situations this can be an important consideration, particularly if electronic components... 

The polymer performance and production efficiency can be enhanced as a function of the basic features of the reinforcement fillers. In the attempt to achieve fillers with increased performance, the following features must be monitored density, flame retardancy, mechanical resistance, thermal conductivity, and magnetic properties. Nanoparticles of carbides, nitrides, and carbonitrides can be used to reinforce polymer matrix nanocomposites with desirable thermal conductivity. However, current trends in the design of these materials reveal that is not enough to choose a wellperforming material for each component of the heat dissipation path. In addition, careful attention must be paid to the manner in which these materials interact with each other. A filler that conducts heat well but does not wet the matrix may lead to poor results compared to a lower conductivity filler that does wet the matrix. In other words, a major fact that leads to interfacial resistance is faulty physical contact between filler and matrix, which primarily depends on surface wettability (Han and Fina2011). 

Chapter 11 also highlights the latest developments in multiphase polymeric materials and composites. Designing thermophysical behavior of polymers with nanometric inclusions for heat dissipation in electronic devices includes the transport abilities of polymers significantly enhanced by the embedding of nanometric inclusions with specific properties. Thermal conduction processes in polymer nanocomposites are described, starting from the matrix itself and continuing with the... 

Figure 7.8 presents measurements of the heat dissipation for selected materials with different thermal and mechanical properties presented as a ratio of the thermal conductivities of the surface to the probe. From the simple Eq. (7.2) for the composite thermal conductivity coefficient, we can conclude that the method should be more sensitive for materials such as polymers with thermal conductivity less than the conductivity of the tip material than it is for materials with higher thermal conductivity (small variation in AQ) (Fig. 7.8). 

Polymer-matrix composites have been used as one of the most common packaging materials for encapsulating a variety of electronic components for dissipating heat [14]. In this section, 3D AlN nanowhiskers with brush-hke structure were filled into the polymer matrix to enhance its thermal conductivity. The 3D brush-hke AlN fiUers were fabricated by CS process [7a], as iUustrated in Section 3.2. The use of AlN as a filler candidate to enhance the thermal conductivity of the polymer is attributed to its attractive properties such as high thermal conductivity, high electrical resistivity, and good chemical stabihty with polymers [1]. To explore the promoting effect of the 3D brush-hke AIN fillers on thermal conductivity, three types of AIN fillers with different brush-hke filler aspect ratio were added into polymer matrix to fabricate a series of composites and their thermal conductivities were measured. The results demonstrated that the 3D brush-hke AIN nanowhiskers fillers can effectively enhance the thermal conductivity of the polymer composite. 

Ablation is understood to be the loss of surface material through thermal effects. This term was originally used in glaceology. The effect is also important in the construction of space capsule heat shields. In contrast to superficial expectations, polymers exhibit quite minor ablation properties, since they absorb, dissipate, and accumulate heat, with, however, changes in the polymeric material. 

Germer [1] has discussed the increasing use of PEEK for miniature electronics. Some examples of these are electrolytic capacitors, potentiomer components and micro-connectors. Ele discusses the thermal, electrical and mechanical properties of this polymer and gives data on permittivity and dissipation factor and heat resistance. 

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