Degradação do polipropileno durante a extrusão e a geração de compostos orgânicos voláteis

Abstract

Resumo: Estudou-se a degradação de um polipropileno copolímero não estabilizado durante a extrusão a diferentes temperaturas (de 180 a 240 °C) e a conseqüente geração de compostos orgânicos voláteis (VOC). Os VOC foram coletados por meio de um condensador de gases, conectado na zona de desgaseificação da extrusora, e analisados por espectrometria no infravermelho (FTIR-ATR). A degradação do polímero foi acompanhada através da cromatografia de exclusão por tamanho e FTIR. À temperatura de 180 °C a degradação do polipropileno não gerou quantidades coletáveis de compostos orgânicos voláteis. Por outro lado, a partir de 200 °C houve geração de compostos olefínicos, não voláteis à temperatura ambiente, que aumentaram em quantidade com o aumento da temperatura de extrusão. A Função de Distribuição de Cisão de Cadeia (CSDF) mostrou que a baixas temperaturas, 180 e 200 °C, o mecanismo de degradação do polipropileno é preferencialmente por cisão de cadeia com alguma ramificação e/ou reticulação. Entretanto, nas temperaturas de extrusão mais altas, 220 e 240 °C, o mecanismo de degradação envolve exclusivamente cisão de cadeia e do tipo preferencial, ou seja, o número de cisões aumenta com o aumento da massa molar inicial da cadeia polimérica original. Palavras-chave: Polipropileno, degradação termo-mecânica, distribuição de massa molar, cisão de cadeia, FTIR, CSDF. Polypropylene Degradation during Extrusion and the Formation of Volatile Organic CompoundsAbstract: The thermo-mechanical degradation of an unstabilized polypropylene copolymer during extrusion at different temperatures (from 180 to 240 °C) and the production of volatile organic compounds (VOC) were studied. VOC's were collected via a volatile condenser, fitted at the degassing exit of the extruder and analyzed via infrared spectroscopy ( FTIR-ATR). The polymer degradation was followed via size exclusion chromatography and FTIR. At low extrusion temperatures (180 °C) the PP degradation produces undetectable quantities of VOC's. On the other hand, starting from 200 °C, there is the formation of olefinic compounds of molecular weight not volatile at room temperature, which increase in quantity with the rise of the extrusion temperature. The Chain Scission Distribution Function (CSDF) shows that at low temperatures (180 and 200 °C) the PP degradation mechanism is preferentially via chain scission with some branching and/or crosslinking in the lower molecular weight. At higher extrusion temperatures (220 and 240 °C) the degradation mechanism is exclusively via chain scission and it is preferential, i.e., the number of chain scission increases with the increase in the initial molecular weight of the original polymeric chain.

A study of the controlled degradation of polypropylene containing pro-oxidant agents

“…Absorbance in the region of 1725 cm -1 and 3500 cm -1 indicated the presence of carbonyl and hydroxyl groups (De Paoli 2008; Cáceres and Canevarolo 2009), respectively, and the absorbance peak at 2722 cm -1 was related to angular molecular vibrations in CH and axial molecular vibrations in CH 3 , as suggested elsewhere (Cáceres and Canevarolo 2009; Babetto and Canevarolo 2002; Rabello and White 1997; Garton et al 1978). Comparison of these absorbances can be used to normalize IR spectra since these peaks are insensitive to the oxidative degradation of pure polypropylene (Wang et al 2011).…”

Lignin as a green primary antioxidant for polypropylene

“…It involves the formation of a free radical at the tertiary carbons of the polymer backbone as initial step. These free radicals react with oxygen generating hydroperoxides, carbonyl groups, and volatile compounds . Thus, free radical scavengers preclude the degradation of polypropylene.…”

Mechanism of Degradation of Starch, a Highly Branched Polymer, during Extrusion

“…In addition, in the extrusion of polyolefins there is a significant influence of reactions of a variety of unsaturated end-groups (e.g., ref ), whereas starch comprises largely “nonreducing” ends (glucose units with an α-(1,4) linkage to the preceding unit) at the end of each branch and, per whole molecule, a single “reducing” end group (a 6-membered ring with three neighboring −OH groups, which can ring-open to a free aldehyde−keto group); in starch, these end-groups do not undergo reaction in extrusion. Cross-linking, − side-chain branching and thermo-oxidative reactions , occur in addition to simple scission in the extrusive degradation of polyolefins, causing an increase in molecular weight and size; the overall size distribution during extrusion is a compound of this increase with the decrease due to simple shear scission. For starch, only simple shear scission (and hence a decrease in molecular weight and size) occurs.…”