Evaluation of the Mechanical and Thermal Properties Decay of PHBV/Sisal and PLA/Sisal Biocomposites at Different Recycle Steps

Environmental sustainability assessment of biodegradable bio-based poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from agro-residues: Production and end-of-life scenarios

In the context of a circular bio-based economy, more public attention has been paid to the environmental sustainability of biodegradable bio-based plastics, particularly plastics produced using emerging biotechnologies, e.g. poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or PHBV. However, this has not been thoroughly investigated in the literature. Therefore, this study aimed to address three aspects regarding the environmental impact of PHBV-based plastic: (i) the potential environmental benefits of scaling up pellet production from pilot to industrial scale and the environmental hotspots at each scale, (ii) the most favourable end-of-life (EOL) scenario for PHBV, and (iii) the environmental performance of PHBV compared to benchmark materials considering both the pellet production and EOL stages. Life cycle assessment (LCA) was implemented using Cumulative Exergy Extraction from the Natural Environment (CEENE) and Environmental Footprint (EF) methods. The results show that, firstly, when upscaling the PHBV pellet production from pilot to industrial scale, a significant environmental benefit can be achieved by reducing electricity and nutrient usage, together with the implementation of better practices such as recycling effluent for diluting feedstock. Moreover, from the circularity perspective, mechanical recycling might be the most favourable EOL scenario for short-life PHBV-based products, using the carbon neutrality approach, as the material remains recycled and hence environmental credits are achieved by substituting recyclates for virgin raw materials. Lastly, PHBV can be environmentally beneficial equal to or even to some extent greater than common bio- and fossil-based plastics produced with well-established technologies. Besides methodological choices, feedstock source and technology specifications (e.g. pure or mixed microbial cultures) were also identified as significant factors contributing to the variations in LCA of (bio)plastics; therefore, transparency in reporting these factors, along with consistency in implementing the methodologies, is crucial for conducting a meaningful comparative LCA.

Impact of Multiple Reprocessing on Properties of Polyhydroxybutyrate and Polypropylene

Biobased plastics have the potential to be sustainable, but to explore their circularity further, current end-of-life options need to be broadened. Mechanical recycling is one of the most accepted methods to bring back plastics into the loop. Polyhydroxybutyrates (PHBs) are biobased and biodegradable in nature with promising properties and varied applications in the market. This study focuses on their potential for mechanical recycling by multiple extrusion cycles (E1-E5) and multi-faceted characterization of the virgin (V) and reprocessed materials from E1 to E5. The behavior is compared to polypropylene (PP) as a reference with a similar property profile, which has also been reprocessed five times. The thermal properties of both series showed a stable melting point and thermal decomposition temperature from thermal analyses (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)). However, a steady increase in the degree of crystallinity was observed which could counterbalance the decrease in molecular weight due to repeated extrusion measured by gel permeation chromatography and resulted in similar values of tensile strength across the cycles. The strain at break was impacted after the first extrusion, but no significant change was observed thereafter; the same was observed for impact strength. Even in scanning electron microscopy (SEM) images, virgin and E5 samples appeared similar, showing the stability of morphological characteristics. Fourier transform infrared spectroscopy (FTIR) results revealed that no new groups are being formed even on repeated processing. The deviation between the PHB and PP series was more predominant in the melt mass flow rate (MFR) and rheology studies. There was a drastic drop in the MFR values in PHB from virgin to E5, whereas not much difference was observed for PP throughout the cycles. This observation was corroborated by frequency sweeps conducted with the parallel plate method. The viscosity dropped from virgin to E1 and E2, but from E3 to E5 it presented similar values. This was in contrast to PP, where all the samples from virgin to E5 had the same values of viscosity. This paper highlights the possibilities of mechanical recycling of PHB and explains why future work with the addition of virgin material and other additives is an area to be explored.

Comparative Verification of the Accuracy of Implant Models Made of PLA, Resin, and Silicone

Polylactic acid (PLA) has gained considerable attention as an alternative to petroleum-based materials due to environmental concerns. We fabricated implant models with fused filament fabrication (FFF) 3D printers using PLA, and the accuracies of these PLA models were compared with those of plaster models made from silicone impressions and resin models made with digital light processing (DLP). A base model was obtained from an impact-training model. The scan body was mounted on the plaster, resin, and PLA models obtained from the base model, and the obtained information was converted to stereolithography (STL) data by the 3D scanner. The base model was then used as a reference, and its data were superimposed onto the STL data of each model using Geomagic control. The horizontal and vertical accuracies of PLA models, as calculated using the Tukey-Kramer method, were 97.2 ± 48.4 and 115.5 ± 15.1 μm, respectively, which suggests that the PLA model is the least accurate among the three models. In both cases, significant differences were found between PLA and gypsum and between the PLA and resin models. However, considering that the misfit of screw-retained implant frames should be ≤150 µm, PLA can be effectively used for fabricating implant models.

Accuracy of Dental Models Fabricated Using Recycled Poly-Lactic Acid

Based on the hypothesis that the fabrication of dental models using fused deposition modeling and poly-lactic acid (PLA), followed by recycling and reusing, would reduce industrial waste, we aimed to compare the accuracies of virgin and recycled PLA models. The PLA models were recycled using a crusher and a filament-manufacturing machine. Virgin PLA was labeled R, and the first, second, and third recycles were labeled R1, R2, and R3, respectively. To determine the accuracies of the virgin and reused PLA models, identical provisional crowns were fitted, and marginal fits were obtained using micro-computed tomography. A marginal fit of 120 µm was deemed acceptable based on previous literature. The mesial, distal, buccal, and palatal centers were set at M, D, B, and P, respectively. The mean value of each measurement point was considered as the result. When comparing the accuracies of R and R1, R2, and R3, significant differences were noted between R and R3 at B, R and R2, R3 at P, and R and R3 at D (p < 0.05). No significant difference was observed at M. This study demonstrates that PLA can be recycled only once owing to accuracy limitations.

Fit accuracy of resin crown on a dental model fabricated using fused deposition modeling 3D printing and a polylactic acid filament

Purpose We considered the possibility of reducing industrial waste by fabricating and reusing dental models prepared using a fused deposition modeling (FDM) 3D printer and polylactic acid (PLA) filaments. The purpose of this study was to verify the accuracy of models fabricated using FDM and PLA.Methods The same provisional crown was used to check the marginal fit on PLA models prepared using an intraoral scanner (IOS) and FDM, plaster models made with silicone impression material and plaster, and resin models prepared using an IOS and stereolithography apparatus (SLA) 3D printer. The marginal fit was measured using micro-computed tomography at four points on the tooth: the buccal center (B), palatal center (P), mesial center (M), and distal center (D) points.Results At point B, the marginal gaps were 118 ± 21.7, 62 ± 16.4, and 50 ± 26.5 μm for the PLA, resin, and plaster models, respectively, with a significant difference between the PLA model and the other two. However, the marginal gap at all other measurement points was not significantly different between the models (P > 0.05).Conclusions We compared the accuracy of the models fabricated using the FDM, SLA, and conventional methods. The combination of FDM and PLA filaments showed no significant differences from the other models, except at point B, indicating its usefulness. Therefore, FDM and PLA may become necessary materials for dental treatment in the future.

Influence of PCL and PHBV on PLLA Thermal and Mechanical Properties in Binary and Ternary Polymer Blends

PLLA, PCL and PHBV are aliphatic polyesters which have been researched and used in a wide range of medical devices, and all three have advantages and disadvantages for specific applications. Blending of these materials is an attractive way to make a material which overcomes the limitations of the individual polymers. Both PCL and PHBV have been evaluated in polymer blends with PLLA in order to provide enhanced properties for specific applications. This paper explores the use of PCL and PHBV together with PLLA in ternary blends with assessment of the thermal, mechanical and processing properties of the resultant polymer blends, with the aim of producing new biomaterials for orthopaedic applications. DSC characterisation is used to demonstrate that the materials can be effectively blended. Blending PCL and PHBV in concentrations of 5-10% with PLLA produces materials with average modulus improved by up to 25%, average strength improved by up to 50% and average elongation at break improved by 4000%, depending on the concentrations of each polymer used. PHBV impacts most on the modulus and strength of the blends, whilst PCL has a greater impact on creep behaviour and viscosity. Blending PCL and PHBV with PLLA offers an effective approach to the development of new polyester-based biomaterials with combinations of mechanical properties which cannot be provided by any of the materials individually.

Acute toxicity of bioplastic leachates to Paracentrotus lividus sea urchin larvae

In an attempt to ensure that bioplastics, progressively replacing petrochemical-derived plastics, do not release any harmful compound to the environment, the study assessed the toxic effects of three innovative bioplastic products: polyhydroxybutyrate resin (PHB), polylactic acid cups (PLA) and a polylactic acid/polyhydroxyalkanoate 3D printing filament (PLA/PHA), together with a synthetic polyvinyl chloride (PVC) toy in Paracentrotus lividus sea urchin larvae. PVC toy was the most toxic material, likely due to the added plasticizers; remarkably, even if PHB is conceived as a nontoxic polymer, it showed a slight toxicity and Gas Chromatography-Mass Spectometry analysis (GC-MS) revealed the presence of a wide range of additives. Conversely, PLA cups and PLA/PHA filament were innocuous for the larvae, a positive outcome for these renewable solutions. Proven that additives are also used in some bioplastic formulations, they should be carefully addressed to ensure that they are as safe as regarded.

Physical Properties and Non-Isothermal Crystallisation Kinetics of Primary Mechanically Recycled Poly(l-lactic acid) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The physical properties and non-isothermal melt- and cold-crystallisation kinetics of poly (l-lactic acid) (PLLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biobased polymers reprocessed by mechanical milling of moulded specimens and followed injection moulding with up to seven recycling cycles are investigated. Non-isothermal crystallisation kinetics are evaluated by the half-time of crystallisation and a procedure based on the mathematical treatment of DSC cumulative crystallisation curves at their inflection point (Kratochvil-Kelnar method). Thermomechanical recycling of PLLA raised structural changes that resulted in an increase in melt flow properties by up to six times, a decrease in the thermal stability by up to 80 °C, a reduction in the melt half-time crystallisation by up to about 40%, an increase in the melt crystallisation start temperature, and an increase in the maximum melt crystallisation rate (up to 2.7 times). Furthermore, reprocessing after the first recycling cycle caused the elimination of cold crystallisation when cooling at a slow rate. These structural changes also lowered the cold crystallisation temperature without impacting the maximum cold crystallisation rate. The structural changes of reprocessed PHBV had no significant effect on the non-isothermal crystallisation kinetics of this material. Additionally, the thermomechanical behaviour of reprocessed PHBV indicates that the technological waste of this biopolymer is suitable for recycling as a reusable additive to the virgin polymer matrix. In the case of reprocessed PLLA, on the other hand, a significant decrease in tensile and flexural strength (by 22% and 46%, respectively) was detected, which reflected changes within the biobased polymer structure. Apart from the elastic modulus, all the other thermomechanical properties of PLLA dropped down with an increasing level of recycling.

Curved-Mechanical Characteristic Measurements of Transparent Conductive Film-Coated Polymer Substrates Using Common-Path Optical Interferometry

This study proposes a method for measuring curved-mechanical characteristics based on a whole-folding test for transparent conductive film-coated polymer substrates using common-path optical interferometry. Accordingly, 80-, 160-, and 230-nm indium tin oxide films coated on 40 × 40 mm 125-μm-thick polyethylene terephthalate (PET) substrates, and monolayer graphene films coated on 40 × 40 mm 250-μm-thick PET substrates are inspected and analyzed under the curving conditions of 50-, 30-, 20-, and 10-mm radii before and after an 11,000 whole-folding cycle test based on a 10-mm folding radius. This study utilizes the changes in the phase retardations of transparent conductive film-coated polymer substrates under different curving conditions before and after 11,000 whole-folding cycles to analyze the substrates’ residual stress characteristics that were the direct result of manufacturing process parameters. The results from this study of curved-mechanical characteristic measurements of flexible transparent conductive substrates can provide designers with improved product development and can assist manufacturers in improving the manufacturing design of enhanced coating processes.

End-of-Life Options for (Bio)degradable Polymers in the Circular Economy

End-of-life options for plastics include recycling and energy recovery (incineration). Taking into account the polymeric waste, recycling is the intentional action that is aimed at reducing the amount of waste deposited in landfills by industrial use of this waste to obtain raw materials and energy. The incineration of waste leads to recovery of the energy only. Recycling methods divide on mechanical (reuse of waste as a full-valuable raw material for further processing), chemical (feedstock recycling), and organic (composting and anaerobic digestion). The type of recycling is selected in terms of the polymeric material, origin of the waste, possible toxicity of the waste, and its flammability. The (bio)degradable polymers show the suitability for every recycling methods. But recycling method should be used in such a form that it is economically justified in a given case. Organic recycling in a circular economy is considered to be the most appropriate technology for the disposal of compostable waste. It is addressed for plastics capable for industrial composting such as cellulose films, starch blends, and polyesters. The biological treatment of organic waste leads also to a decrease of landfills and thereby reducing methane emissions from them. If we add to their biodegradability the absence of toxicity, we have a biotechnological product of great industrial interest. The paper presents the overview on end-of-life options useful for the (bio)degradable polymers. The principles of the circular economy and its today development were also discussed.

Influence of the Degradation Medium on Water Uptake, Morphology, and Chemical Structure of Poly(Lactic Acid)-Sisal Bio-Composites

A series of poly(lactic acid) (PLA) and poly(lactic acid)-based bio-composites (sisal PLA) were prepared and studied by spectroscopic and microscopic techniques as such and after immersion at room temperature in different degradation mediums (i.e., distilled and natural sea water and solutions at pH = 2, 6, and 8). In these conditions, some of their macroscopic and microscopic properties were monitored during a period of 30 days. Water absorption increased with the increasing fiber content regardless of the immersion medium. The maximum water absorption was achieved at pH = 8 (~16%), indicating a more severe action of the alkaline mediums on the samples. The diffusivity, D, of PLA decreased with the addition of fibers and acidic mediums showed higher D, indicating higher diffusivity of water through the specimens with respect to those submerged in moderate or alkaline mediums. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analysis evidenced a weak interaction between the PLA matrix and the sisal fibers. Very limited degradation phenomena occur in our conditions: Despite some changes in the microstructure, the PLA backbone seems to be largely resistant to hydrolysis, almost regardless of the pH value and even at the highest sisal content.

Environmental Degradation of Plastic Composites with Natural Fillers-A Review

Polymer composites are widely used modern-day materials, specially designed to combine good mechanical properties and low density, resulting in a high tensile strength-to-weight ratio. However, materials for outdoor use suffer from the negative effects of environmental factors, loosing properties in various degrees. In particular, natural fillers (particulates or fibers) or components induce biodegradability in the otherwise bio inert matrix of usual commodity plastics. Here we present some aspects found in recent literature related to the effect of aggressive factors such as temperature, mechanical forces, solar radiation, humidity, and biological attack on the properties of plastic composites containing natural fillers.

The Influence of Compatibility on the Structure and Properties of PLA/Lignin Biocomposites by Chemical Modification

Lignin, a natural amorphous three-dimensional aromatic polymer, is investigated as an appropriate filler for biocomposites. The chemical modification of firsthand lignin is an effective pathway to accomplish acetoacetate functional groups replacing polar hydroxyl (–OH) groups, which capacitates lignin to possess better miscibility with poly(lactic acid) (PLA), compared with acidified lignin (Ac-lignin) and butyric lignin (By-lignin), for the sake of blending with poly(lactic acid) (PLA) to constitute a new biopolymer based composites. Generally speaking, the characterization of all PLA composites has been performed taking advantage of Fourier transform infrared (FTIR), scanning electron microscopy (SEM), dynamic Mechanical analysis (DMA), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), rheological analysis, and tensile test. Visibly, it is significant to highlight that the existence of acetoacetate functional groups enhances the miscibility, interfacial compatibility, and interface interaction between acetoacetate lignin (At-lignin) and PLA. Identical conclusions were obtained in this study where PLA/At-lignin biocomposites furthest maintain the tensile strength of pure PLA.

E, Bassyouni M, Zoromba M, Abdel-Aziz M, Mira H, Y. E. Fabrication and Characterization of Microcellular Polyurethane Sisal Biocomposites

In this study, microcellular polyurethane (PU)-natural fiber (NF) biocomposites were fabricated. Polyurethanes based on castor oil and PMDI were synthesized with varying volume ratios of sisal fiber. The effect of natural fiber treatment using water and alkaline solution (1.5% NaOH) and load effect were investigated. Biocomposites were mechanically and physically investigated using tensile, viscoelasticity, and water absorption tests. The interfacial adhesion between PU and sisal fiber was studied using SEM. Short NF loads (3%) showed a significant improvement in the mechanical properties of the PU-sisal composite such as modulus of elasticity, yield and tensile strength up to 133%, 14.35 % and 36.7% respectively. Viscoelastic measurements showed that the composites exhibit an elastic trend as the real compliance (J’) values were higher than those of the imaginary compliance (J’’). Increasing NF loads resulted in a decrease of J’. Applying variable temperatures (120–80 °C) caused an increase in the stiffness at different frequencies.