The aim of this work is to study the effects of different simulated mechanical recycling processes on the structure and properties of PLA. A commercial grade of PLA was melt compounded and compression molded, then subjected to two different recycling processes. The first recycling process consisted of an accelerated ageing and a second melt processing step, while the other recycling process included an accelerated ageing, a demanding washing process and a second melt processing step. The intrinsic viscosity measurements indicate that both recycling processes produce a degradation in PLA, which is more pronounced in the sample subjected to the washing process. DSC results suggest an increase in the mobility of the polymer chains in the recycled materials; however the degree of crystallinity of PLA seems unchanged. The optical, mechanical and gas barrier properties of PLA do not seem to be largely affected by the degradation suffered during the different recycling processes. These results suggest that, despite the degradation of PLA, the impact of the different simulated mechanical recycling processes on the final properties is limited. Thus, the potential use of recycled PLA in packaging applications is not jeopardized.

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ABSTRACT:The reactions of two cellulosic materials (an industrial cellulosic by-product from a Kraft pulp mill facility and a reference material) with three coupling agents, used to improve compatibility between cellulosic reinforcements and thermoplastic matrices, were studied by diffuse reflectance Fourier-transform infrared (DRIFT) spectroscopy and diffuse reflectance ultraviolet-visible spectroscopy. A maleated polypropylene wax (Epolene E-43™) and two silanes (N-2-aminoethyl-3-aminopropyltrimethoxysilane and methyltrimethoxysilane) were used as coupling agents. The two cellulosic materials reacted in a similar way and the three coupling agents were covalently bonded to the cellulose. For the aminosilane, a reaction with cellulose involving a fraction of the amino groups was detected. A simple method, based on the analysis of the oxidation kinetics of treated and untreated materials, was developed to compare the degree of cellulose modification achieved by each coupling agent. The analysis revealed that a reduced fraction of the cellulose reactive groups was converted by esterification with the maleated polypropylene. However, when applied in the appropriate conditions, the two silanes converted most of such cellulose reactive groups. Finally, the reaction of cellulose with mixtures of coupling agents was studied. The aminosilane-treated cellulose reacted with the maleated polypropylene with formation of amide links.

Recently, the use of natural materials has grown in the plastics industry. In this study, silk fibroin nanoparticle (SFNP) was successfully synthesized from silk fibroin (SF) and analyzed by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained results revealed that the well-ordered domains in SF were changed to an amorphous structure in SFNP and it was attributed to the cleavage of SF polypeptide chains upon acid hydrolysis. Then several blends of poly(lactic acid)/poly(Ԑ-caprolactone) (PLA/PCL) containing different amounts of PCL were prepared and characterized. Based on the test results the best properties were achieved in the blend with 30% of PCL. The addition of 1% of SFNP into this blend enhanced the compatibility between PLA and PCL and reduced the PCL droplet size from 1.170±92 μm to 794±46 nm, this was observed by scanning electron microscopy (SEM). Thermal analysis indicated that the presence of SFNP caused an improvement of thermal degradation stability of the PLA/PCL blend in the end set temperature range. The crystallization process also slowed and the crystal growth rate decreased from 0.34 to 0.31 min-1. Additionally, the use of SFNP increased (9.7%) the hardness value and reduced (15.7%) the water vapor permeability value of the PLA/PCL blend. The results of these experiments demonstrated that the prepared PLA/PCL/SFNP green nanocomposites have good potential for the food packaging applications.

3D printing PLA wastes were recovered from a well-known reference grade and from different sources. The recovered wastes were subjected to an energic washing step and then reprocessed into films by melt-extrusion, followed by compression molding to simulate the industrial processing conditions. The obtained materials were characterized and the optical, structural, thermal and crystallization behavior are reported. The mechanical recycling process leads to an increase of the crystallinity and a decrease of the intrinsic viscosity of the formulations, particularly in the sample based on blends of different 3D-PLA wastes. Moreover, the obtained films were disintegrated under composting conditions in less than one month and it was observed that recycled materials degrade somewhat faster than the starting 3D-PLA filament, as a consequence of the presence of shorter polymer chains. Finally, to increase the molecular weight of the recycled materials, the 3D-PLA wastes were submitted to a solid-state polymerization process at 110, 120, and 130 °C, observing that the recycled 3D-wastes materials based on a well-known reference grade experiences an improvement of the intrinsic viscosity, while that coming from different sources showed no significant changes. Thus, the results show that 3D printing PLA products provides an ideal environment for the implementation of distributed recycling program, in which wastes coming from well-known PLA grades can successfully be processed in films with good overall performance.

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