A kinetic model of polymer degradation during extrusion

El'darov, E.G.; Mamedov, F.V.; Gol'dberg, V.M.; Заиков, Г. Е.

doi:10.1016/0141-3910(95)00160-3

Cited by 45 publications

(21 citation statements)

References 2 publications

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“…Na literatura dos anos 70 [8,9] pode-se encontrar uma equação que utiliza a massa molar numérica media (M n ) da amostra antes e após ter sofrido degradação, que segundo os autores, permite calcular o número de cisões de cadeia, e que vem sendo utilizada freqüentemente na literatura [10][11][12][13][14][15] . Pode-se também encontrar outras equações que utilizam relações entre Peterson et al [20] estudaram a degradação térmica do poliestireno através da termogravimetria e calorimetria diferencial de varredura (DSC) sob atmosferas de nitrogênio e ar.…”

Section: Introductionunclassified

Cisão de cadeia na degradação termo-mecânica do poliestireno sob múltiplas extrusões

Cáceres

Canevarolo

2008

Polímeros

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Resumo: Determinou-se o número de cisões de cadeia gerado pela degradação termo-mecânica do poliestireno quando submetido a múltiplas extrusões. A degradação foi acompanhada pelas mudanças nas curvas de distribuição de massa molar. Seguindo-se o significado físico das massas molares médias de uma curva de MWD mostrou-se que a massa molar numérica media M n é a única que pode ser relacionada diretamente com o número de moléculas do sistema. A partir desta calculou-se o número de cadeias clivadas (ns) como uma relação entre a M n da amostra degradada e a virgem. A função de distribuição de cisão de cadeia (CSDF) mostra que o processo de degradação termo-mecânica do poliestireno submetido a múltiplas extrusões à 240 °C é do tipo aleatório, independente da massa molar inicial. Palavras-chave:Degradação termo-mecânica, extrusão, poliestireno, cisão de cadeia. Chain Scission in the Thermo Mechanical Degradation of Polystyrene under Multiple ExtrusionsAbstract: The number of chain scissions during thermo-degradation of polystyrene under multiple extrusions was calculated. The degradation produces changes in the molecular weight distribution MWD curves. Following the physical meaning of the average molecular weights of a MWD curve it was shown that the number average molecular weight M n is the only average that can be directly related to the number of molecules in the system. From that it was calculated the number of sectioned chains (ns) as a ratio between the number of chains in the degraded and original polymers. The chain scission distribution function (CSDF) shows that the thermo-mechanical degradation process of polystyrene under multiple extrusions at 240 °C is of a random type, independent of the initial molecular weight.Keywords: Thermo-mechanical degradation, extrusion, polystyrene, chain scission. IntroduçãoDurante o processo de propagação da cadeia radical na polimerização em cadeia os centro ativos da frente em crescimento se instabilizam e morrem aleatoriamente, o qual gera cadeias poliméricas com diferentes tamanhos, formando uma distribuição de tamanhos em torno de um valor mé-dio, o que exige uma curva de distribuição de massa molar (MWD) para representá-lo. A partir de 1964 [1] a cromatografia de exclusão por tamanho (SEC) tem sido extensivamente utilizada na caracterização de polímeros, através da obtenção das curvas de distribuição de massa molar (MWD). A análise das curvas de MWD pode ajudar no entendimento das propriedades físico-químicas dos polímeros incluindose a elucidação dos processos de degradação termo-mecâ-nica. Infelizmente a análise destas curvas é ainda difícil e não está completamente equacionada. Assim a maioria das publicações se restringe a analise das mudanças nas massas molares médias, não explorando apropriadamente todas as informações contidas em uma curva de MWD.Para melhor entender os processos de degradação que ocorrem durante o processamento termo-mecânico de um polímero foi proposta uma metodologia de cálculo [2,3] que permite quantificar o deslocamento total da curva de M...

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Section: Introductionunclassified

Cisão de cadeia na degradação termo-mecânica do poliestireno sob múltiplas extrusões

Cáceres

Canevarolo

2008

Polímeros

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“…Processing of APIs that have high melting points or are thermally labile continues to be a challenge due to energy input required during HME to produce an amorphous final product (17,18). Additionally, higher molecular weight polymers that may be effective for stabilizing the amorphous drug may be too viscous for processing via HME due to high torque loads, requiring the use of plasticizers that decrease the final product glass transition temperature (19)(20)(21)(22).…”

Section: Introductionmentioning

confidence: 99%

Thermal Processing of PVP- and HPMC-Based Amorphous Solid Dispersions

et al. 2015

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Abstract. Thermal processing technologies continue to gain interest in pharmaceutical manufacturing. However, the types and grades of polymers that can be utilized in common thermal processing technologies, such as hot-melt extrusion (HME), are often limited by thermal or rheological factors. The objectives of the present study were to compare and contrast two thermal processing methods, HME and KinetiSol® Dispersing (KSD), and investigate the influence of polymer type, polymer molecular weight, and drug loading on the ability to produce amorphous solid dispersions (ASDs) containing the model compound griseofulvin (GRIS). Dispersions were analyzed by a variety of imaging, solid-state, thermal, and solution-state techniques. Dispersions were prepared by both HME and KSD using polyvinylpyrrolidone (PVP) K17 or hydroxypropyl methylcellulose (HPMC) E5. Dispersions were only prepared by KSD using higher molecular weight grades of HPMC and PVP, as these could not be extruded under the conditions selected. Powder X-ray diffraction (PXRD) analysis showed that dispersions prepared by HME were amorphous at 10% and 20% drug load; however, it showed significant crystallinity at 40% drug load. PXRD analysis of KSD samples showed all formulations and drug loads to be amorphous with the exception of trace crystallinity seen in PVP K17 and PVP K30 samples at 40% drug load. These results were further supported by other analytical techniques. KSD produced amorphous dispersions at higher drug loads than could be prepared by HME, as well as with higher molecular weight polymers that were not processable by HME, due to its higher rate of shear and torque output.

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“…El'darov et al [6] verified a concurrence of degradation mechanisms for polyethylene during extrusion and the depletion of oxygen along single screw extruder length. Pinheiro, Chinelatto and Canevarolo [4,5] observed the same behavior for HDPE during multiple extrusions in twin screw extruder and internal mixer processing.…”

Section: Introductionmentioning

confidence: 99%

“…This group has its concentration increased with temperature as a result of and increase in kinetic formation of it: the heat provided increases the oxygen reaction rate with macroradicals [4][5][6][7][8][9][10][11][12][13][14][15][16][17] . On the other hand, number of extrusions yields more alkyl radicals to react with oxygen.…”

Section: Parameters Influence On Transvinylene Concentrationmentioning

confidence: 99%

“…Reprocessing is one reasonable alternative to reuse LDPE and other polymers [2] . The most common way to provide it is by extrusion, in a method called mechanical recycling; however, this process subjects the polymer to a set of degradations: mechanical by shear stress, thermal by the action of temperature, and oxidative because of the presence of oxygen [3][4][5][6] . Besides this, all polymeric material is subjected to a set of degradative agents, like electromagnetic radiations, temperature and chemicals, not only in processing step, but during all its life cycle.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Reprocessing in the formation of functional groups during low density polyethylene aging

et al. 2012

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Abstract:In recent years, the interest in polymer recycling has increased. However, in every reprocessing step the material undergoes shear stress and is affected by temperature and oxygen. The aim of this paper is to investigate the influence of multiple extrusion in the generation of functional groups, namely hydroperoxide, carbonyl, and transvinylene. Low density polyethylene was reprocessed three times in a single screw extruder. In each recycling step hot pressed films were prepared. These films were submitted to a heat treatment in an oven with air circulation and renovation to proceed with aging tests at different times and temperatures. The results obtained showed that all functional groups had their concentration increased with the increase in number of reprocessing, the aging time and temperature of the heat treatment. The factorial design was applied to verify the influence of these parameters. All the parameters had significant effects, since their regression coefficients had the same order of magnitude, with the most influential parameter being the aging temperature, followed by the aging time and number of extrusions. Most of the interactions were influential, indicating that the formation of functional groups depends upon their interaction, and not only on their isolated effects.

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A kinetic model of polymer degradation during extrusion

Cited by 45 publications

References 2 publications

Cisão de cadeia na degradação termo-mecânica do poliestireno sob múltiplas extrusões

Cisão de cadeia na degradação termo-mecânica do poliestireno sob múltiplas extrusões

Thermal Processing of PVP- and HPMC-Based Amorphous Solid Dispersions

Influence of Reprocessing in the formation of functional groups during low density polyethylene aging

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