Characterization of thermoplastic starch/poly(lactic acid) blends obtained by extrusion and thermopressing

Abstract

Blendas de poli(ácido láctico)(PLA) e amido termoplástico (TPS) foram preparadas por extrusão e moldagem por compressão utilizando 0,1, 0,2 e 0,3 g de PLA per g de TPS. O TPS foi obtido por extrusão utilizando 0,25 e 0,30 g de glicerol por g de amido. Foram avaliadas as propriedades mecânicas e de barreira ao vapor de água, e determinadas as isotermas de sorção de umidade. A morfologia dos materiais foi avaliada através de microscopia eletrônica de varredura e as propriedades térmicas dos polímeros puros e das blendas, através de calorimetria diferencial de varredura (DSC). A microscopia e os resultados de DSC indicaram a imiscibilidade da blenda e a presença de duas fases. Nas blendas contendo 20% e 30% de PLA observou-se um aumento da tensão de ruptura e do módulo elástico. A blenda contendo 30% de PLA apresentou uma redução da permeabilidade ao vapor de água, comportamento associado à redução do coeficiente de difusão observada nesta amostra.Blends of poly(lactic acid) (PLA)/thermoplastic starch (TPS) were prepared by extrusion and thermopressing, with proportions of 0.1, 0.2 and 0.3 g of PLA per g TPS. Thermoplastic starch was obtained from the extrusion of 0.30 g or 0.25 g of glycerol per g of starch. The mechanical properties and water vapor permeability were tested and water sorption isotherms were obtained. The morphological characteristics of the samples were observed through scanning electron microscopy (SEM) and the thermal properties of the pure polymers and the blends by differential scanning calorimetry (DSC). The SEM and DSC results indicated the immiscibility of the TPS/ PLA blends and the presence of two phases. For blends with 20% and 30% of PLA increases in the tensile strength and modulus were observed. The lowest water vapor permeability was observed for the blend with 30% of PLA, which is related to the lowest diffusion coefficient value observed for this sample.

Adipate and Citrate Esters as Plasticizers for Poly(Lactic Acid)/Thermoplastic Starch Sheets

“…The C parameter, which is associated with the sorption heat of the monolayer, was higher for DEA sheets, and the magnitude of this parameter was in agreement with values reported in other studies of PLA/TPS blends [37].…”

“…The GAB model represented the experimental data (R 2 [ 0.99) well, and this model is adequate for describing the water sorption isotherms of the TPS films [27,31,36], and the TPS/PLA blends [37].…”

Poly(lactic acid)/thermoplastic starch sheets: effect of adipate esters on the morphological, mechanical and barrier properties

“…Comparing the obtained results with other results reported in the literature, lower values of the tensile strength, Young's modulus and elongation at break were obtained in PLA/TPS (30 g PLA / 100 g TPS) films produced by extrusion and thermopressing [29,30] In this case, because TPS was the continuous phase, it was responsible for the mechanical properties of the films, resulting in more fragile materials. PLA/TPS films (20% TPS) with increased resistance were produced by Teixeira et al [34] due the addition of cassava bagasse.…”

“…The values obtained are lower than those observed for cassava starch films [35,36] and PLA/TPS films [29] and greater than PLA films with synthetic phenolic antioxidants added [37] . The presence of PLA promoted a hydrophobic character of the material and was responsible for decreasing the WVP because the material permeability is strongly influenced by the hydrophobic or hydrophilic nature of its components.…”

“…In the sheets with higher proportions of PLA, some spaces between the PLA and TPS phases were evident, showing the interface between the polymers. This result could be associated with poor interaction and incompatibility between the starch and PLA because of the difference in hydrophobicity, as observed in other reports [7,[12][13][14]17,18,[29][30][31] . Confocal laser microscopy (CLM) is usually employed to study the surface morphology of polymeric films and sheets and confer information about the surface topography and heterogeneity.…”