Structural changes of PVC in PVC/LDPE melt‐blends: Effects of LDPE content and number of extrusions

Abstract

This paper investigates the structural changes of polyvinyl chloride (PVC) in melt‐blends of a low‐density polyethylene (LDPE) and polyvinyl chloride (PVC), and the effects of LDPE content and number of extrusion passes. These effects were examined in terms of changes in weight average molecular weight and number average molecular weight, polyene and carbonyl indices, color changes of the blend, and the variations in glass transition and decomposition temperatures. It was found that loading LDPE into PVC led to the formation of short‐chain LDPE grafted PVC (s‐LDPE‐g‐PVC) copolymers, via a macro‐radical cross‐recombination reaction, which had greater weight average molecular weight with unchanged number average molecular weight, increased decomposition temperature, lower glass transition temperature, as compared to the pure PVC sample. The dehydrochlorination reaction of PVC was suppressed by the macro‐radical cross‐recombination reaction with addition of LDPE, the effect being more pronounced at 13.0 wt% LDPE. For a given LDPE content, the macro‐radical cross‐recombination and dehydrochlorination reactions competed with one another, thus causing the increases in molecular weight average and molecular weight number up to the 4th extrusion pass. At the 5th extrusion pass, the dehydrochlorination reaction was predominant owing to a depletion of LDPE content to be grafted onto PVC molecular chains. The glass transition and decomposition temperature decreased with increasing number of extrusion passes. Polym. Eng. Sci. 44:487–495, 2004. © 2004 Society of Plastics Engineers.

Synergism of pentaerythritol-zinc with β-diketone and calcium stearate in poly(vinyl chloride) thermal stability

“…The degradation of PVC usually proceeds through a dehydrochlorination process, which results in the formation of long conjugated double bonds or polyene sequences, -(-CH ¼ CH-)-n , which causes a color change. 3,4 Various methods have been developed to address this problem. Among these methods, the most efficient and practical is the addition of thermal stabilizers to PVC to protect against thermal degradation.…”

Effect of wood sawdust content on rheological and structural changes, and thermo‐mechanical properties of PVC/sawdust composites

“…Processors are strongly advised to take special care for PVC/natural fibre composites because PVC is usually thermally unstable, especially under elevated temperatures, presence of oxygen, humidity and mechanical stresses. The degradation of PVC is usually proceeded by a dehydrochlorination process, which results in the formation of long conjugated double bonds or polyene sequences (—CHCH—) n , causing a colour change 11, 12. The dehydrochlorination process becomes even more rapid in the presence of oxygen, and results in formation of carbonyl groups.…”

Insights into the use of zinc–mannitol alkoxide as a novel thermal stabilizer for rigid poly(vinyl chloride)

“…Actually, this detrimentally autocatalytic degradation phenomenon was not observed in PVC stabilized with Zn–Man within 180 min. The possible reason was that there was no free ZnCl 2 produced in the degradation of the PVC stabilized with Zn–Man, as illustrated in reaction III in Scheme , and thus, no catalytic effect of ZnCl 2 was observed.…”