Polypropylene degradation reactions

The catalytic degradation of polypropylene was carried out over ferrierite catalyst using a thermogravimetric analyzer as well as a fixed bed batch reactor. The activation of reaction was lowered by adding ferrierite catalyst, which was similar with that from ZSM-5. Ferrierite produced less gaseous products than HZSM-5, where the yields of i-butene and olefin over ferrierite were higher than that over HZSM-5. In the case of liquid product, main product over ferrierite is C5 hydrocarbon, while products were distributed over mainly C7-C9 over HZSM-5. Ferrierite showed excellent catalytic stability for polypropylene degradation. 

Degradation reactions Degradation of polypropylene by shear-heating, degradation of PET with ethylene glycol... 

Mechanisms of Degradation Inhibitors. The degradation mechanisms described above have no little effect on end-use stability and processing stability of polypropylene. Indeed, without stabilizers and antioxidants to inhibit such degradation reactions, polypropylene would have limited usefulness as a structural plastic if any usefulness at all. 

Blends of Polypropylene and Poly(Methyl Methacrylate). In seeking explanations for the experimental observations in blend degradations, it is important to consider the form in which the polymer is being degraded. Since compatibility, especially in polymers as unlike chemically as PP and PMMA, is the exception rather than the rule and since the blend samples were translucent, it seems most likely that the low concentration component, PMMA, is dispersed as discrete micelles in a matrix of PP. Thus, any interaction between the degradation reactions of the two components must occur across a fairly well defined phase boundary. Because of the severe restrictions on the motion of macromolecules... 

Coiai, S., Passaglia, E., Aglietto, M., and Ciardelli, R 2004. Control of degradation reactions during radical functionalization of polypropylene in the melt. Macromolecules 37 8414-8423. 

Shortly after controlled degradation technology was developed, pioneer workers explored polypropylene functionalization reactions in extruders (1). The early work involved grafting of maleic anhydride onto polypropylene to improve adhesion properties. Later work involved grafting other monomers, and even polymers, onto polypropylene in twin-screw extruders. 

This basic mechanism has been used to model the degradation reactions of polypropylene in an extruder (5-7). 

The thermal degradation reactions were carried out at a barrel temperature of 230°C, whereas peroxide-induced degradation reactions were catalyzed by injecting 2,5-dimethyl-2,5-fc i-(t-butylperoxy) hexane at rates of 0.05, 0.1, and 0.2 phr (per hundred parts resin) into the feed hopper of the extruder. The polypropylene resin was supplied by Himont and had a melt flow index of 0.14 g/10 min. 

The thermal degradation of mixtures of the common automotive plastics polypropylene, ABS, PVC, and polyurethane can produce low molecular weight chemicals (57). Composition of the blend affected reaction rates. Sequential thermolysis and gasification of commingled plastics found in other waste streams to produce a syngas containing primarily carbon monoxide and hydrogen has been reported (58). 

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

In Europe, interest has centered particularly on polyhydroxybutyrate, which can be made into films for packaging as well as into molded items. The polymer degrades within 4 weeks in landfills, both by ester hydrolysis and by an ElcB elimination reaction of the oxygen atom p to the carbonyl group. The use of polyhydroxybutyrate is limited at present by its cost—about four times that of polypropylene. 

---