Comportamento reológico do Bio-PE e do PCL na presença do PEgAA e PEgMA

Abstract

RESUMOO reômetro de torque é um equipamento que reproduz em escala laboratorial o processamento de polímeros. Neste equipamento, a velocidade de rotação dos rotores, temperatura e tempo de processamento são parâme-tros predeterminados e impostos ao sistema investigado; avalia-se o torque necessário para a fusão, mistura e homogeneização da amostra. Através do gráfico do torque em função do tempo e do gráfico da temperatura em função do tempo de processamento, cujos valores estão relacionados com as propriedades reológicas, estrutura e massa molar das amostras, é possível obter informações sobre o comportamento dos polímeros em fluxo, ou seja, durante o processamento. Neste trabalho, foi investigado o efeito do polietileno graftizado com ácido acrílico (PEgAA) e do polietileno graftizado com anidrido maléico (PEgMA) no biopolietileno (Bio-PE) e no poli(ε-caprolactona) (PCL) por reometria de torque. Foi verificado que o PEgAA e o PEgMA promoveram aumento no torque dos sistemas Bio-PE/PEgAA, Bio-PE/PEgMA, PCL/PEgAA e PCL/PEgMA, possivelmente resultante de interações e/ou reações químicas ocorridas nesses sistemas poliméricos. Espectros de FTIR evidenciaram possíveis interações e/ou reações químicas entre os grupos funcionais dos políme-ros grafitizados e o Bio-PE e o PCL. Valores de torque mais altos foram observados nos sistemas com parâ-metros de solubilidade (δ) mais próximos, corroborando com os cálculos propostos por Hansen. Palavras-chave:Bio-PE, PCL, PEgAA, PEgMA, reometria de torque, parâmetro de solubilidade. ABSTRACTThe torque rheometer is equipment that enables to simulate the polymer processing in a laboratory scale. A set of parameters, i.e., rotor speed, temperature and processing time are predefined and imposed to the compounds under analysis. The necessary torque for melting and mixing the compound is measured. Through the plots of torque as a function of time and temperature, which are linked to the rheological properties, microstructure and molar weight of the samples, it is possible to acquire information regarding the flow behavior of polymers, meaning during processing. In this work, the effect of acrylic acid-grafted polyethylene (PEgAA) and maleic anhydride-grafted polyethylene (PEgMA) in bio-polyethylene (Bio-PE) and in poly(ε-caprolactone) (PCL) was performed by torque rheometry. PEgAA and PEgMA increased the torque rheometry values of the polymeric systems under investigation, i.e, Bio-PE/PEgAA, Bio-PE/PEgMA, PCL/PEgAA and PCL/PEgMA, possibly due to chemical interaction and/or reactions occurred during the processing. FTIR spectra presented possible interactions and/or chemical reactions between the functional groups of grafted polymers and Bio-PE and PCL. Higher torques were observed for the systems with similar solubility parameters agreeing with the mathematical calculations provided by Hansen.

Toughening of bio-PE upon addition of PCL and PEgAA

“…Addition of PEgAA increased the interfacial adhesion, due to the chemical interaction between the hydroxyl group of PCL and the acrylic acid group, as also reported by Bezerra et al (2017a). Therefore, the incorporation of PEgAA provided a better ad-hesion among the phases, decreasing the dispersed phase and contributing to the morphology stabilization of polymer blends compared to the noncompatibilized ones (Sánchez et al, 2001, Moura et al, 2008, Liu et al, 2011, Pracella, 2016Agrawal et al, 2018).…”

“…This increase was approximately 83.5% for Bio-PE/PCL/ PEgAA (80/20/10 w/w/phr) and 60.5% for Bio-PE/PCL/PEgAA (70/30/10 w/w/ phr). This behavior can be associated to the higher adhesion among the phases increasing PCL content (20 and 30%), as a result of reaction between acrylic acid groups and hydroxyl ones of PCL, as well as the miscibility of PEgAA with Bio-PE, which properly promotes stress transferring from one to each other phase (Deblieck et al, 2011;Silva, 2014;Bezerra et al, 2017a;Chudnovsky and Sehanobish, 2017;Agrawal et al, 2018). Even though addition of the coupling agent did not improve the impact strength, when compared to a respective blend without functionalized copolymer, the morphology reached by SEM showed that the dispersed phase decreased and the morphology stabilized.…”

Compatibility and characterization of Bio-PE/PCL blends

“…DSC scans acquired during the second heating are presented in Figure 2 The Molten Fraction plots presented a sigmoidal shape characteristic of phase transformation in polymers without discontinuities, behavior similar to that observed during crystallization from the melt (Relative Crystallinity); these curves are presented in Appendix 3, Figures A8-A11. The melting rates of PCL and Bio-PE increased in the blends with values between 30-50% higher than in the neat resins, which can be understood as a facilitated melting process, thus providing a processing with less energy consuming and possibly cheaper [23,24] .…”

“…These results are linked to the morphological effect among the phases, despite the immiscible character (as observed by DSC scans Figure 2, SEM images Figure 3, Table A1-A4 and Figures A6-A7 of Appendix 2 and 3), in the amorphous phases of both polymers, secondary interactions are possible to occur, additionally PEgMA contributes to better mechanical performance. SEM images captured with the aim of a better enlightenment, and shown further on [30,33,34] , suggest the Elongation at Break of Bio-PE/PCL blends, being the ternary systems with addition of the functionalized copolymer PEgMA improved (higher), which can be resulted from the reaction between maleic anhydride with the hydroxyl (OH) end groups of PCL that may be taken place providing an interface with higher performance, behaviors which can be inferred from decreases in dispersed phase as showed in Figure 3 and Table 4 by dispersed phase's average diameter measurements [24,25,[35][36][37][38][39][40] .…”

“…The addition of PEgMA also contributed to increase the impact strength, where increases of 133.2% for Bio-PE/PCL/PEgMA (80/20/10 phr) and 100.3% for Bio-PE/PCL/PEgMA (70/30/10 phr) were reached. This behavior can be attributed to the higher amount of linkages between Bio-PE/PCL phases promoted by the reaction trough maleic anhydride and hydroxyl groups of PCL, as well as the compatibility of PEgMA with Bio-PE, which efficiently drives the tension transfer mechanisms between the phases (Bio-PE matrix and PCL dispersed phase, see SEM images) [24,33,38] . In Figure 3a-d is observed the surfaces of Bio-PE and PCL with characteristics of ductile fracture evidencing the elastic deformation followed by the plastic one, these images corroborate the previous results obtained with mechanical tests where deformations higher than 500% were reached for the neat polymers.…”