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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•Two different simulated mechanical recycling processes for PLA were studied.•The mechanical recycling caused a decrease of the molecular weight of PLA.•Mechanical recycling did not largely affect the structure or the properties of PLA.•Mechanically recycled PLA could be used in packaging applications.•Mechanical recycling is a valid method for valorization of PLA wastes.
The influence of nanoclays on the structural changes of hydrated poly(l-lactic acid) (PLLA) was investigated at two temperatures, above and below its Tg. Samples of a commercial PLLA and ...nanocomposites with 2 wt% of an organically modified montmorillonite and an unmodified halloysite were kept in a phosphate buffered solution for different times at 37 and 58 °C and then characterized. The crystallinity degrees and the nature of the crystalline structures developed were determined by differential scanning calorimetry, X-Ray Diffraction and Fourier Transform infrared spectroscopy. While in the cold crystallization of PLLA in dry conditions the α form is obtained only above 100 °C, different mixtures of α and α′ forms were obtained in water at 58 °C, depending on the clay used. The hydrolytic degradation of PLLA played a main role in the structural transformations found at long immersion times, since the short chains formed allowed greater crystallinity degrees and leaded to more perfect crystals. PLLA structure is changed by clays because of its ability as nucleating agents but also due to its effect on the hydrolytic degradation. The unmodified tubular halloysite inhibited degradation, so that lower degrees of crystallinity were obtained in the halloysite based nanocomposite. On the other hand, the modified montmorillonite acted as catalyst of degradation, which explained the appearance of crystalline structures in the nanocomposite with montmorillonite after 84 days of immersion at 37 °C.
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•Mixtures of α and α′ polymorphs are developed in hydrated PLLA at 58 °C.•Hydrolysis plays a main role in the PLLA crystallization at long immersion times.•The crystallization of hydrated PLLA depends on the chemical nature of the clay.•Montmorillonite induces the crystallization of hydrated PLLA even at 37 °C.
Poly(lactic acid) (PLA) is a biobased polymer that represents one of the most interesting alternatives to fossil-fuel based polymers in food packaging applications. Most of the PLA used in food ...packaging is used only once and then discarded, even though the PLA types used in packaging have good properties and stability. Therefore, it seems reasonable to consider the possibility of recycling the used polymer through a mechanical recycling process. The main aims of this work are to study the effect of the mechanical recycling on the properties of PLA and the usefulness of different upgrading methods to obtain recycled PLA with improved properties. A commercial type of PLA was subjected to accelerated thermal, photochemical and hydrolytic aging and then reprocessed. During reprocessing, aged PLA was blended with virgin PLA and a commercial chain extender was added. Results point out that recycling causes the degradation of PLA, and negatively affects the thermal stability and mechanical properties. However, addition of virgin PLA, and the chain extender, led to an increase of up to 9% in the intrinsic viscosity and 8% in the Vickers hardness of the recycled material. These results suggest that mechanically recycled PLA with improved performance can be obtained, a fact which might improve the recyclability of PLA and thus the environmental impact of this material.
The growing use of poly(lactic acid) (PLA) and PLA-based nanocomposites in packaging has raised the interest of studying the mechanical recycling of the wastes and the properties of the recycled ...materials. The main objective of this work was to study the effect of two different mechanical recycling processes on the structure and properties of a PLA-montmorillonite nanocomposite. The two recycling processes included accelerated thermal and photochemical aging steps to simulate the degradation experienced by post-consumer plastics during their service life. One of them also included a demanding washing process prior to the reprocessing. A decrease in the molecular weight of PLA was observed in the recycled materials, especially in those subjected to the washing step, which explained the small decrease in microhardness and the increased water uptake at long immersion times. Water absorption at short immersion times was similar in virgin and recycled materials and was accurately described using a Fickian model. The recycled materials showed increased thermal, optical and gas barrier properties due to the improved clay dispersion that was observed by XRD and TEM analysis. The results suggest that recycled PLA-clay nanocomposites can be used in demanding applications.
From an environmental point of view, mechanical recycling is, in general, a good end-of-life option for poly(lactic acid) (PLA), one of the most important biobased polymers. However, the degradation ...of PLA during the service life and, especially, during the mechanical recycling process, leads to a decrease in the properties of PLA, thus reducing the applications of the recycled plastic. The main aim of this work was to study the addition of small amounts of halloysite nanotubes, during the recycling step, as the basis of a cost-effective method for improving the properties of the recycled PLA. Raw halloysite was modified with an aminosilane, and 2% by weight of both raw and modified halloysite were melt compounded with PLA previously subjected to accelerated ageing. The addition of the nanotubes led to recycled materials with improved properties because halloysite reduces the degradation of PLA by blocking the carboxyl groups, generated during the ageing and washing steps, which catalyze the degradation during the recycling process. This effect was more intense in the silanized nanotubes, because the carboxyl groups were effectively blocked by acid–base interactions with the amino groups of the chemical modification. The properties of the recycled plastic with only 2 wt% of silanized halloysite were very close to those of the virgin plastic.
Incorporation of a small content of undecenoic acid is proposed as an approach to introduce polar groups within the macromolecular architecture of high density polyethylene-based materials in order ...to promote an easier degradation after their useful service life. The influence of these hydrophilic groups during thermo and photo-oxidation processes has been then evaluated by several complementary techniques. In addition to different degradation rates, distinct ratios of oxidized species (lactones, ketones, carboxylic acids, esters and aldehydes) are found depending on: a) the initial material (neat high density polyethylene or ethylene-co-undecenoic acid copolymer); b) the type of oxidation (thermo or photoinduced); and c) the absence or presence of a specific prodegradant additive. An important increase of crystallinity has been observed in the final oxidized samples, indicating that the extent of degradation is rather significant.
During the melt processing of nanocomposites with layered silicates, polycarbonates (PC) suffer a severe degradation which causes a great reduction of the mechanical and thermal properties. With the ...overall goal of obtaining clays that cause less degradation of PC, we have studied in this work the degradation of a PC during the melt compounding with three organically modified clays, a commercial one (Cloisite™ 15A) and two clays modified in our laboratory. The laboratory clays were obtained by treating sodium montmorillonite with polyethylenimine or a novel silane which contains the bisphenol-A group. The composites were characterized by Fourier Transform Infrared Spectroscopy and Transmission Electron Microscopy. The PC degradation was measured by Ultraviolet Spectroscopy, Thermogravimetry, Dilute Solution Viscosimetry and Fluorescence Spectroscopy. The second goal of this work was to study the relationships between the results obtained from the different experimental techniques. Some of the studied clays cause a significant increase in the hydrolytic degradation of PC during the melt processing, as shown by the reduction of the average molar mass as well as the appearance of a weight loss step at low temperatures in the thermogravimetric analysis. The formation of phenolic compounds in the degradation process was observed in the fluorescence emission and the UV absorption spectra. The relative effect of the different clays on the PC degradations depends more on factors such as the chemical nature of the organic modification of the clay or the degree of dispersion of the clay into the polymer, than on other factors such as the apparent water content of the clay.
New organically modified clays have been obtained using a polyelectrolyte and a novel bisphenol-A-containing silane as modifiers. The properties and applications of the modified clays depend on the ...reaction conditions.
New organically modified clays have been obtained from sodium montmorillonite, using either a cationic polyelectrolyte (polyethylenimine) or a novel homemade bisphenol-A silane as modifiers. The modification processes have been carried out in different reaction media, in order to study the effects on the properties of the modified clays of several reaction parameters, such as the pH of the polyethylenimine solution or the nature of the solvent used in the silanization. The obtained clays were characterized using X-ray diffraction, thermogravimetric analysis, and FTIR spectroscopy. Clays modified with polyelectrolyte or silane show significant increases in the basal spacing. The properties of polyelectrolyte-modified clays depend on the pH of the treating solution. The increase in the basal spacing of polyelectrolyte-modified clays varies only slightly with the pH; however, this reaction parameter clearly determines the total amount of polyelectrolyte introduced in the clay. The properties and applications of silane-modified clays are strongly dependent on the presence of water in the reaction media used for the silanization. These results have been explained by considering that the reaction conditions determine the nature and the amount of material intercalated into the clay.
The chemical interactions between cellulose and chitosan were studied in chitosan-treated celluloses using diffuse reflectance spectroscopic techniques (UV–Vis and FTIR) and fluorescence ...spectroscopy. The materials were obtained by treating pure cotton cellulose with chitosan in dilute acetic acid solutions of different concentration, and some samples were exposed to different thermal treatments in air. Other related materials, including cellulose treated with benzyl amine and chitosan-treated with acetaldehyde, were also prepared and studied as models for chitosan-treated celluloses. The spectra of the treated celluloses showed new absorption and emission bands that revealed the existence of chemical interactions. These bands were assigned to conjugated imines produced in the reaction of the chitosan amino groups with cellulose carbonyl groups. The reaction is strongly amplified at temperatures above 100
°C, causing the intense yellowing of chitosan-treated celluloses.
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•Mechanical characterisation of nanoclay–polycarbonate nanocomposites by DSI.•Homogeneity of nanofiller distribution assessing by means of DSI techniques.•Nanoclay compounding on ...polycarbonate: reinforcement vs. decrease of molar mass.•Recovery of waste polycarbonates by melt compounding with nanoclays.
The preparation of recovered polycarbonate matrix nanocomposites filled with organic modified montmorillonites has been considered as a method for the secondary or mechanical recycling of these polymeric wastes. The mechanical properties of these nanocomposites have been evaluated by means of Depth Sensing Indentation measurements. The selection of the measurement conditions has been discussed and a method to evaluate the heterogeneity of these materials has been presented. It has been found that greater nanoclay contents do not always lead to increase in mechanical properties. This fact has been explained in terms of the competition between the reinforcement effect of the nanofiller and the thermal and mechanical degradation that experiments the matrix during the melt processing. This result provide a limit for the clay addition in the mechanical recovery of polycarbonate wastes.
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