4. Sample melted for 10 minutes before crystallization
The melting of the perfectly crystalline substance is an equilibrium process characterized by a marked volume changed and well defined temperature. The disappearance of a polymer crystalline phase at the melting point is accomplished by changes in physical properties, since crystalline melting point may be determined by noting the temperature of disappearance of the last traces of crystallinity as evidence by birefringence observed between crossed polarized on a hot stage microscope.
5. Appearance of slowly crystallized and quenched sample
According to the graph it is found that crystallization take place with respect to time and also it is found that mobility of chains are restricted in quenched sample.
The development of crystallinity in polymer is not instantaneous. According to the graph spherulite growth is the function of time at temperature below the crystalline melting point. As the temperature is lowered, the rate of crystallization increases, so the mobility of the molecules decreases. Where as the spherulite in polymer quenched from the melt and then held at temperature in between Tm and Tg is additional evidence of high chain mobility below tm. The existence of mobile lattice defects provides a plausible in crystalline material. It has been found, as might be expected, that the ease with these molecular motions takes place decreases as molecular weight increases.
6. Melting temperature of polypropylene
Temperature from literature = 170° C
Temperature from experiment = 165
7. The behavior of the polymer melt during rapid cooling in the mould determines, to a great extent, the quality and usability of a final product. Technical raw materials are often equipped with nucleating agents in order to obtain crystallization within the desired temperature range and at the required rate.
At slow cooling rate, larger crystals were formed, whereas at fast cooling rate, smaller crystals appeared together. Slowly crystallized samples had a broader distribution of crystal size. Crystallization temperatures had a similar effect as cooling rate. At higher crystallization temperatures, larger crystals and a broader crystal size distribution were found. Agitation rate had a marked effect on crystal size. Higher agitation rates lead to smaller crystal size. Cooling rate was the most influential parameter in crystal thermal behavior and composition. Slowly crystallized samples showed a broader melting diagram and an enrichment of long-chain. Crystallization behavior was more related to processing conditions of injection moulding.
References
Billmeyer, FW., Text Book of Polymer Science, 3rd ed., John Wiley and Sons, New York, 1984
Cowie, Blakie, J.M.G., Polymers: Chemistry & Physics of Modern Material, 1991
Parker, D.B.V., Polymer Chemistry, 3rd ed., Applied Science Publishers, London, 1974
Williams,D.J., Polymer Science and Engineering, 1971
Appendices
1. Spherulite growth at different temperature
2.1. Spherulite growth rate Calculation
Spherulite can be calculated by:
G= spherulite sie = μm
Time min
Sample A @ 130° C
G = 0.5/22 = 0.023 μm/min
Sample B @ 128° C
G = 0.21/6 = 0.035 μm/min
Sample C @ 126° C
G = 0.3/8 = 0.038 μm/min
Sample D @ 124° C
G = 0.17/3 = 0.057 μm/min
2.2. Spherulite growth Vs Temperature
