Plastics heat content

In flnidized bed sinter coating, the heated substrate is dipped into a fluidized bed of the plastic powder. A 0.1- to 1.5-mm-thick film is formed, depending on the heat content of the part. 

The plasticity and heat content of fresh TSP (or SSP) make it much easier to granulate than cured TSP less recycle, water, and steam are required. Presumably, less fuel is required for drying. Total electric power consumption is somewhat lower, and labor requirements are only 36% of that required for the conventional" two-step process. The product is said to be superior in hardness, shape, uniformity, and smoothness. 

In contrast to the other plastic crystal substance DMP, the HMP did not volatilize from the fabric when it was dried at conventional or elevated temperature to remove excess water. The modified fabrics had heat contents of 87.78-104.5 J/g on heating and 79.42-96.14 J/g on cooling after one to ten thermal cycles. The heat contents of HMP-treated fabrics were 1.7-2.5 times those of untreated fabrics. The fabrics are not suitable for clothing textiles, due to their high phase change temperature. 

This process includes the recovery of energy content only. Most plastic waste has a high heat content so can be incinerated the generation of heat energy is the only advantage of this process. The solid waste problem is not solved by this process in fact it leads to the issue of air pollution. 

This means that polymer flammability decreases when LOI increases. This method is also used to test the efficiency of flame retardants, but it is necessary to mention the direction of gas flow while testing (i.e., if the gases are coming from above or below the burning sample) [11]. Relative flammabilities as determined by LOI do not always agree with results from other tests it is thus necessary to know these results for a good evaluation of the flammability of plastic materials. Table 12.2 shows that there is no direct relation between LOI and the enthalpy or heat content for some polymers. 

Figure 1.1 Enthalpy (heat content) vs. temperature. Comparison of data for typical crystalline material (naphthalene) with those for crystalline (acetal copolymer) and amorphous (polycarbonate) plastics...

A number of advantages are to be gained by extrusion of plastics at relatively low melt temperatures for example, a melt at a low temperature is more viscous and therefore retains its shape more easily, shorter time and distance are necessary for subsequent cooling because of the small heat content in the melt, and the risk of thermal degradation is reduced. 

During the cooling of the component, the heat is drawn from it by the mould. The amount of heat involved depends on the component weight, the type of plastic (specific heat content), the ejection temperature, and the cycle frequency. The mould passes this heat to the environment (by heat conduction to the machine and by radiation or convection to the ambient air), if no special temperature control system is connected up. The higher the mould temperature, the greater the amount of heat released to the environment. So, when the machine starts up, the mould initially heats up to the temperature at which the amount of heat supplied by the solidifying and cooling plastic can be released to the environment. 

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