> Why PVC heat stabilizers and processing
Why PVC heat stabilizers and processing
2014-02-20 by seoer8
Ideal PVC structure is the first - the tail structure -CH2-CHCl-CH2-CHCl-, is quite stable . But so far the synthesis method can not be like PVC synthetic butadiene rubber as a catalyst in the role of Jigger be oriented so that there are rules cis-butadiene polymerization .
Free radical polymerization of vinyl chloride is polymerized random , in addition to its first stable - tail structure , and the PVC heat stabilizer for profile first - the first structure - CH2-CHCl-CHCl-CH-, tail - tail structure -CHCl-CH2-CH2-CHCl - ; vinyl Results generated with coupling disproportionation CH2 = CH-CHCl-CH2- , and allyl chloride structure -CH2-CH = CH-CHCl-CH2 and the like.
Generating allyl chloride, chlorine and tertiary carbon double bond in the synthesis of PVC is its molecular chain structure is unstable factors of instability order : PVC internal molecular chain allyl chloride > tertiary carbon chloro > allyl end groups chloride > Chung chlorine. It is easily degraded because of instability in the structure of PVC molecular chains exist , if not for stabilization when modified PVC processing , the decomposition temperature is about 130 ℃, but that the PVC resin processing into useful products , molding temperature to at 190 ℃ or more. Thus , heat stabilizers must be added to improve its structure is stabilized .
So pvc needs to be added during the synthesis PVC heat stabilizers.