Halogenated sorbitol derivatives using as nucleating agent and their effect on orientation of polypropylene fiber
In this work, two halogenated derivatives of benzylidene sorbitol were synthesized by reacting D-sorbitol with an aromatic aldehyde in the present of an acid catalyst. ie.chloro and bromo derivatives for using as nucleating agent for polypropylene. For chloro derivative, different positions of substituent (ortho, meta and para) were also synthesised. SEM and TEM micrographs of gel extracted from organic solvent revealed long fibril network of chloro and bromo substitutes which their diameters are in the range of about 10-200 nm. Small amount (0.1-1%wt) of these materials was blended with isotactic polypropylene (iPP) by two roll mill machine and the mixture was made to fiber form by extrusion. It was found that these fibrils formed in polymer melt and shear flow during fiber preparation process. The effect of fiber preparation conditions such as die temperature, screw speed and crystallization rate on crystal orientation of polypropylene were studied. The effect of halogenated sorbitol derivatives on the crystallization of iPP were studied using different scanning calorimeter technique. It was found that 0.5 wt% of para chloro derivative show the most effective as a nucleating agent for iPP compared to the other substitution positions. The crystallization temperature of iPP containing 0.5 wt% of para chloro sorbitol increases up to 15% compared to the crystallization of neat PP. The para bromo shows less effective in an increasing the crystallization temperature when compared to the para chloro. No further increase in the crystallization temperature when the amounts of all derivatives are higher than 0.5%wt. It was found that the beta structure of iPP can be changed to alpha structure when small amount of sorbitol derivatives are presented below their solubility temperature.
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