Which of the following is not a strengthening mechanism in t

Which of the following is not a strengthening mechanism in thermoplastics? Bulky side groups Highly polar atoms Chain length Grain size How many grams of sulphur are needed to crosslink 5.0 % of the crosslink sites in 100 g of polyisoprene rubber? Assume 1.0 sulphur atoms per crosslink. Atomic weight of S = 32. 2.35 g 1.47 g 4.63 g 0.93 g A BCC unit cell has an atomic radius of 1.0 units. What is the volume of the unit cell in cubic units? 10.1 15.7 5.4 12.3 A FCC unit cell has a = 1.0 units. What is the planar density on the (1 0 0) plane atoms per square units? 1.41 1.73 1.00 2.0

Solution

Answer: d) grain size

Different strengthening mechanisms in the thermoplastics:

a) Bulky side groups:Thermoplastics can be permanently deformed by chain slippage mechanisms. This can be avoided by introducing bulky side groups. For example introducing pendant atomics group on the main carbon chains increase the strength greatly

b) Highly polar atoms:In thermoplastics, the intermolecular forces between the chains is increased by a high polar atoms bonded to the main chains. This leads to increase in strength of the thermoplastics

c) Chain Length: When the average length of the chain increases, the number of molecules from various chains that are bonded to each other also increases. This way the strength also increases