Durability of biodegradable polymers for the conservation of cultural heritage

The use of polymers for conservation of cultural heritage is related to the possibility to slow down or stop natural deterioration which, in many cases, corresponds to stopping the entrance of liquid water and to favor spontaneous water vapor removal. Unfortunately, hydrophobicity is generally favored by surface roughness and thus competitive with transparency. It is therefore important to find an optimal balance hydrophobicity, transparency and durability (especially to photooxidation). However, polymers typically used for applications in this field come from non-renewable resources and are not biodegradable. In this work, the mechanical, structural, and optical properties of PLA, PBAT, and a PBAT/PLA blends, as well as surface properties and water vapor permeability, were investigated before and after exposure to UV irradiation, in order to evaluate their durability and suitability for conservation of cultural heritage

Effect of moisture content on the processing and mechanical properties of a biodegradable polyester

This work is focused on the influence of moisture content on the processing and mechanical properties of a biodegradable polyester used for applications in injection molding. The pellets of the biodegradable polyester were exposed under different relative humidity conditions at a constant temperature before being compression molded. The compression-molded specimens were again placed under the above conditions before the mechanical testing. With all these samples, it is possible to determine the effect of moisture content on the processing and mechanical properties separately, as well as the combined effect of moisture content on the mechanical properties. The results obtained showed that the amount of absorbed water—both before processing and before mechanical testing— causes an increase in elongation at break and a slight reduction of the elastic modulus and tensile strength. These changes have been associated with possible hydrolytic degradation during the compression molding process and, in particular, with the plasticizing action of the moisture absorbed by the specimens

Recycling of Heterogeneous Mixed Waste Polymers through Reactive Mixing

Anything that is not recycled and/or recovered from waste represents a loss of raw materials. Recycling plastics can help to reduce this loss and to reduce greenhouse gases, improving the goal of the decarbonization of plastic. While the recycling of single polymers is well assessed, the recycling of mixed plastics is very difficult because of the strong incompatibility among the different polymers usually present in urban waste. In this work, heterogeneous mixed polymers, i.e., polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylenetherephthalate (PET) were processed using a laboratory mixer under different conditions of temperature, rotational speed and time to evaluate the effect of the above parameters on morphology, viscosity and mechanical properties of the final blends. Morphological analysis shows a strong incompatibility between the polyethylene matrix and the other dispersed polymers. The blends show, of course, a brittle behavior, but this behavior slightly improves with decreasing temperature and increasing rotational speed. A brittle-ductile transition was observed only at a high level of mechanical stress obtained by increasing rotational speed and decreasing temperature and processing time. This behavior has been attributed to both a decrease in the dimensions of the particles of the dispersed phase and to the formation of a small amount of copolymers that act as adhesion promoters between matrix and dispersed phases

An additive model to predict the rheological and mechanical properties of polypropylene blends made by virgin and reprocessed components

In this work, an additive model for the prediction of the rheological and mechanical properties of monopolymer blends made by virgin and reprocessed components is proposed. A polypropylene sample has been reprocessed more times in an extruder and monopolymer blends have been prepared by simulating an industrial process. The scraps are exposed to regrinding and are melt reprocessed before mixing with the virgin polymer. The reprocessed polymer is, then, subjected to some thermomechanical degradation. Rheological and mechanical experimental data have been compared with the theoretical predictions. The results obtained showed that the values of this simple additive model are a very good fit for the experimental values of both rheological and mechanical properties

Recycling of a multilayer barrier food packaging through the use of a nanofiller: Effect of post-consumer plastic bag conditions

Barrier food packaging films result very difficult to recycle since they are multilayer films composed by at least two different materials. In this context, aim of this study was to assess the use of a nanofiller for the mechanical recycling of multilayer barrier plastic bags used for food vacuum packaging. In particular, graphene nanoplatelets (GnPs) were used as nanofiller studying the effect of their concentration on the properties of the nanocomposites obtained by using polyamide (PA)/polyethylene (PE) bags as polymeric matrix. Moreover, the effect of plastic bags life conditions on the nanocomposite properties were evaluated by exposing the multilayer films to accelerated weathering or to contact with a fatty food simulant (olive oil). The results indicated that the incorporation of GnPs led to an enhancement of the morphology of the polymer blends, consequently resulting in nanocomposites with increased stiffness without a drastic reduction in ductility. The nanocomposites produced using post-consumer bags exhibited lower properties compared to materials produced using pre-consumer bags. However, even in this case, the addition of GnPs contributed to an improvement in the properties demonstrating that the use of this nanofiller can be a viable method to recycle multilayer packaging

Influence of a biodegradable contaminant on the mechanical recycling of a low-density polyethylene sample

Mechanical recycling of oil-derived polymers is certainly our best option to reduce pollution, save raw materials, and protect ourselves and the environment from the adverse effects of waste disposal. However, the presence of contaminants, including other types of plastics, that are mixed in during the recycling collection process or during the mechanical waste sorting stage could adversely affect the quality of the recycled product, leading to the recycling of a poor-quality secondary material. In this work, the influence of a biodegradable contaminant on the mechanical recycling of a low-density polyethylene (LDPE) sample was investigated by rheological (shear and non-isothermal elongation) and mechanical analyses. The results showed that 2% of the contaminant is able to influence the rheological, shear, and isothermal elongation properties of recycled LDPE, while the results of the mechanical tests showed that after one extrusion cycle, the main tensile properties were not significantly affected by the presence of the contaminant, but after only two cycles of extrusions, some significant reduction in the final properties began to appear. In short, the presence of 2% of a biodegradable co-polyester in a LDPE matrix gives rise to a more pronounced decay of the rheological and mechanical properties, but, after two extrusion steps, both rheological and mechanical properties seem still useful for the production of film

Investigation on the properties and on the photo-oxidation behaviour of polypropylene/fumed silica nanocomposites

This work investigates the effects of very small amounts of fumed silica on the morphology and on the rheological and mechanical behaviour of polypropylene nanocomposites and on their photo-oxidation behaviour. Polypropylene nanocomposites were prepared using a twin-screw corotating extruder with 0, 1 and 2 wt/wt% of SiO2. Morphological, mechanical, thermomechanical and rheological properties were examined. It was found that the viscosity of the matrix is reduced by the presence of the silica nanoparticles, suggesting a poor adhesion between the two phases and probably some lubricating effect. On the contrary, the mechanical and, in particular, the thermomechanical properties of the matrix are considerably improved by the presence of the silica. In particular, elastic modulus and tensile strength increases remarkably, and this effect becomes more and more remarkable with an increasing temperature. As for the photo-oxidation behaviour, the presence of silica improves the photostability of the polypropylene matrix. This effect has been attributed to both the barrier to the oxygen and to the absorbance of the UV radiation from the silica nanoparticles. Finally, no significant effect of the silica nanoparticles has been put in evidence on the crystallisation behaviour of the polypropylene. As for the effect of the silica content, the difference in the properties of the two nanocomposites is relatively small and all the measured properties depend much less than linearly with its amount. This has been correlated with the reaggregation of the nanoparticles that, having a larger size, decrease the contact area between the matrix and the filler

Toward the Decarbonization of Plastic: Monopolymer Blend of Virgin and Recycled Bio-Based, Biodegradable Polymer

Decarbonization of plastics is based on two main pillars: bio-based polymers and recycling. Mechanical recycling of biodegradable polymers could improve the social, economic and environmental impact of the use of these materials. In this regard, the aim of this study was to investigate whether concentrations of the same recycled biopolymer could significantly affect the rheological and mechanical properties of biodegradable monopolymer blends. Monopolymer blends are blends made of the same polymers, virgin and recycled. A sample of commercially available biodegradable blend was reprocessed in a single-screw extruder until two extrusion cycles were completed. These samples were exposed to grinding and melt reprocessed with 75% and 90% of the same virgin polymer. The blends were characterized by tensile tests and rheological tests. The results obtained showed that while multiple extrusions affected the mechanical and rheological properties of the polymer, the concentration of the reprocessed material present in the blends only very slightly affected the properties of the virgin material. In addition, the experimentally observed trends were accurately predicted by the additive model adopted

Analysis on Isotropic and Anisotropic Samples of Polypropylene/Polyethyleneterephthalate Blend/Graphene Nanoplatelets Nanocomposites: Effects of a Rubbery Compatibilizer

Over the past few years, polymer nanocomposites have garnered a significant amount of interest from both the scientific community and industry due to their remarkable versatility and wide range of potential uses in various fields, including automotive, electronics, medicine, textiles and environmental applications. In this regard, this study focuses on the influence of a compatibilizer rubber on a nanocomposite incorporating graphene nanoparticles (GNPs), with a polymer matrix based on a blend of polypropylene (PP) and polyethylene terephthalate (PET). This effect has been investigated on both isotropic samples and on anisotropic/spun fiber samples. The influence of the compatibilizer rubber on morphological, rheological and mechanical properties was analysed and discussed. Mechanical and morphological properties were evaluated on both isotropic samples obtained by compression moulding and melt-spun fibers. The addition of the rubbery compatibilizer increased the viscosity, improving interfacial adhesion, and the same effect was observed for the melt strength and breaking stretching ratios. Mechanical properties, including the elastic modulus, tensile strength and elongation at break, improved in both types of samples but more significantly in the fibers. These improvements were attributed to the orientation of the matrix, the formation of PET microfibrils, and the reduction in the size of graphene nanoparticles due to the action of the elongational flow. This reduction, facilitated by the elongation flow and the action of the compatibilizer, improved matrix-nanofiller adhesion due to the increased contact area between the two polymeric phases and between the filler and matrix. Finally, a transition from brittle to ductile behaviour was observed, particularly in the system with the compatibilizer, attributed to defect reduction and improved stress transmission