Structure-properties relationships in melt reprocessed PLA/hydrotalcites nanocomposites

Abstract

Abstract. In this work the effect of multiple reprocessing was studied on molecular structure, morphology and properties of poly(lactic acid)/hydrotalcites (PLA/HT) nanocomposites compared to neat PLA. In addition, the influence of two different kinds of HT -organically modified (OM-HT) and unmodified (U-HT) -was evaluated. Thermo-mechanical degradation was induced by means of five subsequent extrusion cycles. The performance of the recycled materials was investigated by mechanical and rheological tests, differential scanning calorimetry (DSC), intrinsic viscosity measurements and SEM observation. The results indicated that the best morphology was achieved in the systems incorporating OM-HT. On increasing the extrusion reprocessing cycles, the properties showed behavior due to two opposite effects: i) chain scission due to thermo-mechanical degradation and ii) filler dispersion effect resulting from multiple processing. In particular, at low reprocessing cycles, both tensile and rheological properties seem to be mainly affected by HT dispersion, especially when OM-HT was added. After five reprocessing cycles, on the contrary, chain scission, i.e. thermo-mechanical degradation, dominated. As regards the effect of the presence of organic modifier in HT, the results indicated that this variable apparently did not affect the macroscopic performance of the nanocomposites, especially at high reprocessing cycles.

Effects of Aging and Different Mechanical Recycling Processes on the Structure and Properties of Poly(lactic acid)-clay Nanocomposites

“…These results are very important, since an improvement of the clay dispersion could lead to enhanced mechanical, optical and gas barrier properties. These results agree with those obtained by Scaffaro et al in PLA nanocomposites with 5% hydrotalcites, where an improvement of the clay dispersion was observed scanning electron microscopy (SEM) [23].…”

“…However, the decrease is very small because the improved dispersion of the clay platelets in the recycled nanocomposites causes an increase on the hardness of the samples, thus partially counteracting the negative effect of the degradation of PLA during the different mechanical recycling processes. A similar behavior was observed by Scaffaro et al in PLA/hydrotalcites nanocomposites, which showed an increase of the Young modulus even after three reprocessing steps [23]. The moderate impact of the recycling processes on the hardness seems to indicate that the mechanical properties of the recycled materials should not be a limiting factor when considering the use of recycled PLA based materials in packaging applications.…”

“…They reported that reprocessing caused an improvement of the dispersion of the clay particles, which led to an increase of the mechanical properties in the first three reprocessing steps. However, after four and five reprocessing cycles, the degradation of PLA was severe, thus decreasing the performance of the material [23]. In both cited works, the degradation of the material during its service life and possible washing steps were not considered.…”

Effect of D‐lactide content of annealed poly(lactic acid) on its thermal, mechanical, heat deflection temperature, and creep properties

“…In most publications (dealing with single PLA grades thus not stereocomplex), the development conditions of the practically beneficial α and α' was investigated as it is developed during cooling at melt processing. Since in most thermoplastic processing technologies high cooling rate is applied and the crystallisation rate of PLA is slow [28], thus it is rather difficult to generate significant crystallinity in the final PLA product only if nucleating agents are used [29][30][31]. At the same time, as PLA crystallizes between Tm and Tg, thus if low crystallinity was achieved during cooling from melt, the possibility of post-production annealing (heating the produced part above Tg and letting its crystallization to complete) is still open.…”

Estudio de la viabilidad del reciclado mecánico del poli(ácido láctico) y sus nanocomposites

“…Además, la degradación del polímero genera cadenas más cortas, las cuales pueden penetrar mejor entre las láminas de arcilla, mejorando también la dispersión. Resultados similares han sido reportados por Scaffaro et al [104], tras someter mezclas de PLA con 5% de hidrotalcita modificada orgánicamente a dos ciclos de extrusión consecutivos en una extrusora de doble husillo. Además de las fotografías de TEM, se realizaron ensayos de XRD en los nanocomposites con C30 para obtener más información de los cambios observados en la morfología de estos materiales después de ser sometidos a los diferentes procesos de reciclado.…”