Plastics Thermo-setting

In practice, synthetic polymers are sometimes divided into two classes, thermosetting and thermo-plastic. Those polymers which in their original condition will flow and can be moulded by heat and pressme, but which in their finished or cured gtate cannot be re-softened or moulded are known as thermo setting (examples phenol formaldehyde or urea formaldehyde polymer). Thermoplastic polymers can be resoftened and remoulded by heat (examples ethylene polymers and polymers of acrylic esters). 

True synthetic polymers came into use when Bakeland came from Belgium and applied his knowledge of the formation of a moldable plastic from phenol and formaldehyde to give the product named Bakelite. This was about 1914. This product, under heat and pressure, set up to a thermo-setting resin and had useful properties especially as an insulating material for electrical items. 

Thermoplastics still soften when heated and harden again when cooled, because there is little or no bonding between individual molecular chains. Thermo sets show three-dimensional structures and rather than softening, thermally decompose while heating. All commodity plastics are thermoplastic. 

CgHjOH(s), used as a disinfectant and in the production of thermo-setting plastics = -3053 kj/mol. 

Thermo set polyesters are typical of the thermoset plastics—the characteristics of which are good temperature resistance, good tensile strength and stiffness, a high degree of hardness, low impact strength unmodified, low extensibility, and generally superior resistance to creep and cold flow. Properties of some typical materials are shown in Table 1-4. 

Themo-plastic materials are those which can be repeatedly softened and melted when heated. Thermo-sets are another gronp of materials, which can be molded once by heat and pressure. They cannot be resoftened, as reheating causes the material to degrade. The latter is commonly not used for food packaging. 

Using this system, roller materials were adjusted so that the ratio of the weight of BF and PP could be set at 50 50. Roller materials were supplied to the TSE and BE-reinforced PP pellets were manufactured. The screw rotated at a speed of 180 rpm and the sleeve temperature was set as 180 °C. In order to check the effectivity of this system, the tensile and flexural strengths with and without the system were compared. The results obtained are shown in figure 5.17. Bamboo fiber reinforced thermo plastics-automatically (BFRTP-AT)shows the case where... 

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