Strategies for strengthening toughened poly(lactic acid) blend via natural reinforcement with enhanced biodegradability: A review

The growing popularity of poly(lactic acid) (PLA) can be attributed to its favorable attributes, such as excellent compostability and robust mechanical properties. Two notable limitations of PLA are its high brittleness and slow biodegradation rate. Both of blending and copolymerization strategies work well to improve PLA's toughness while sacrificing the good tensile strength and modulus properties of PLA. One of the most effective and economical approaches to address this challenge is to incorporate natural reinforcing agents into the toughened PLA system, thereby simultaneously promoting the biodegradation rate of PLA. Nevertheless, the enhancement of tensile strength and modulus is accompanied by a notable decrease in elongation. Therefore, this review provides comprehensive information on the literature works related to the tensile strength, modulus, elongation at break and impact strength of the toughened PLA and its natural fiber reinforced composites. The impact of natural reinforcing agent on the tensile fracture mechanism as well as the synergistic effect on strengthening and toughening performance will be discussed. This review also focuses on the factors boosting the biodegradability of toughened PLA blend by using natural reinforcing fiber. Review presents potential future insights into the development of biodegradable and balanced strengthened-toughened PLA based advanced materials.

PLA-Based Hybrid Biocomposites: Effects of Fiber Type, Fiber Content, and Annealing on Thermal and Mechanical Properties

In this study, we utilized a hybridization approach for two different fibers to overcome the drawbacks of single-fiber-reinforced PLA composites. Coir fiber and bamboo leaf fiber were used as reinforcing natural fibers as their properties complement one another. Additionally, we combined thermal annealing with hybridization techniques to further improve the overall properties of the composites. The results showed that the hybridization of BF: CF with a ratio of 1:2 gave PLA-based hybrid composites optimal mechanical and thermal properties. Furthermore, the improvement in the thermal stability of hybrid composites, attributable to an increase in crystallinity, was a result of thermal annealing. The improvement in HDT in annealed 1BF:2CF hybrid composite was about 13.76% higher than that of the neat PLA. Annealing of the composites led to increased crystallinity, which was confirmed using differential scanning calorimetry (DSC). The synergistic effect of hybridization and annealing, leading to the improvement in the thermal properties, opened up the possibilities for the use of PLA-based composites. In this study, we demonstrated that a combined technique can be utilized as a strategy for improving the properties of 100% biocomposites and help overcome some limitations of the use of PLA in many applications.

Mechanical Behaviour and Impact of Various Fibres Embedded with Eggshell Powder Epoxy Resin Biocomposite

Natural fiber composites are becoming an alternate material to synthetic fiber composites, and the use of eggshell bio-filler has been explored in polymer composites as environmental protection. Jute, coir, and sisal fibers were utilized in this research to make composites out of natural fibers. Polymer composites were made using epoxy resin with different amounts of eggshell powder (ESP) as fillers (2%, 4%, 6%, 8%, and 10% of weight). The mechanical and biodegradability properties of the synthesized composites were investigated. The testing results showed that composites with an optimum percentage of 6% ESP as filler improved mechanical characteristics significantly in all three fiber composites. Among the three fibers, coir fiber with 6% ESP added showed a substantial increase in tensile, flexural, impact, and hardness strength properties by 34.64%, 48.50%, 33.33%, and 35.03%, respectively. In addition, the percentage weight loss of coir fiber composites at 9 weeks is noteworthy in terms of biodegradability testing. As a result, epoxy composites containing eggshell fillers could be employed in applications requiring better tensile, flexural, impact, and hardness strength.

Effect of lyocell fiber cross-sectional shape on structure and properties of lyocell/PLA composites

Three kinds of lyocell fibers with different cross-sectional profiles including circular, Y-shape, and H-shape (abbreviated as O-, Y-, and H-lyocell) and similar mechanical properties were used to reinforce polylactic acid (PLA) by melt compounding and injection molding. The influence of lyocell cross-section shape on the interfacial shearing force, interface morphology, and mechanical properties of lyocell/PLA composites was investigated. Single fiber pull-out tests showed that the interfacial shearing force between lyocell fibers and PLA matrix was in the order of H-lyocell > Y-lyocell > O-lyocell, which was correlated with the fiber non-roundness factor. The higher the non-roundness factor of lyocell fibers, the better were the mechanical properties of lyocell/PLA composites. The tensile strength, impact strength, and initial dynamic storage modulus of different lyocell/PLA composites were in the order of H-lyocell/PLA > Y-lyocell/PLA > O-lyocell/PLA, which was attributed to higher interfacial contact area and stronger interfacial adhesion of profiled lyocell/PLA composites. Therefore, profiled lyocell fibers may be more promising for use in bio-composite reinforcement than conventional circular lyocell fibers.

Critical Review on Polylactic Acid: Properties, Structure, Processing, Biocomposites, and Nanocomposites

Composite materials are emerging as a vital entity for the sustainable development of both humans and the environment. Polylactic acid (PLA) has been recognized as a potential polymer candidate with attractive characteristics for applications in both the engineering and medical sectors. Hence, the present article throws lights on the essential physical and mechanical properties of PLA that can be beneficial for the development of composites, biocomposites, films, porous gels, and so on. The article discusses various processes that can be utilized in the fabrication of PLA-based composites. In a later section, we have a detailed discourse on the various composites and nanocomposites-based PLA along with the properties’ comparisons, discussing our investigation on the effects of various fibers, fillers, and nanofillers on the mechanical, thermal, and wear properties of PLA. Lastly, the various applications in which PLA is used extensively are discussed in detail.

Modification of Fibres and Matrices in Natural Fibre Reinforced Polymer Composites: A Comprehensive Review

Composite materials derived from eco-friendly natural fibres and other biodegradable materials have gained prominence in industrial applications due to their sustainability and reduced greenhouse gas emissions attributes in comparison with conventional reinforcements such as glass and carbon fibres. Application of natural fibre-polymer composites (NFPCs) in different industrial applications provides competitive edge due to its lightweight, higher specific mechanical properties than glass fibres, sustainability and lesser cost involved in production. There are certain challenges associated with natural fibers and its reinforcement in composites such as poor bonding between the fibres and matrix due to its contradictory nature of characteristics, moisture absorption, lower thermal properties and poor interfacial adhesion between the natural fibre and polymer matrix. The challenges involved in NFPCs needs to be overcome to produce materials with relatively equivalent properties to that of conventional compositesand other metallic structures. Several researchers around the globe have conducted investigations with the primary attention being paid to the modification of natural fibers and matrix by employing surface treatments and other chemical treatment methods. In order to address the need for eco-friendly and sustainable materials in different domains, a comprehensive review on natural fibers and its sources, available matrix materials, modification techniques, mechanical and thermal properties of NFPCs is needed for better understanding of behavior of NFPCs.This work provides the information and wholistic view of natural fibre reinforced composites based on the results obtained from modification techniques,with the view of focusing the review in terms of different chemical and physical treatment techniques, modification of fibers and matrix and enhanced mechanical and thermal properties in the composites. This article is protected by copyright. All rights reserved.

Banana Fiber-Reinforced Epoxy Composites: Mechanical Properties and Fire Retardancy

Currently, the growing field of technology has paved the way for using environmental friendly resources; in particular, plant origin holds ecological concern and renewable aspects. Currently, natural fiber composites have widening attention, thanks to their eco-friendly properties. In the present work, the composite material is reinforced with natural fibers from the bark of banana trees (banana fibers), a material available in Vietnam. Banana fibers are extracted from banana peels, pretreated with NaOH 5%, and then cut to an average length of 30 mm. Banana fiber is reinforced for epoxy resin Epikote 240 with mass percents: 10 wt.%, 15 wt.%, 20 wt.%, and 25 wt.%. The results were evaluated through structural morphology (SEM), mechanical properties, fire resistance, and thermal properties. Experimental results show that the tensile, compressive, and impact strengths of biosynthetic materials up to 20% by weight have increased compared to epoxy neat. Flame retardant and thermal properties are kept stable; 20 wt.% banana fiber gives a limiting oxygen index of 20.8% and satisfactory thermal stability.

Towards More Sustainable Materials for Geo-Environmental Engineering: The Case of Geogrids

Plastic materials are widely used in geotechnical engineering, especially as geosynthetics. The use of plastic-based products involves serious environmental risks caused by their degradation. Innovative research has been focusing on biodegradable polymers of natural origin, especially on poly(lactic acid) (PLA), to reduce the use of plastics. This study aims to explore the potentiality of biopolymers for the production of geogrids, measuring the chemical and mechanical characteristics of raw materials and of prototype samples, similar to those available on the market. First, chemical composition and optical purity were determined by hydrogen nuclear magnetic resonance (1H-NMR) and polarimetry. Furthermore, samples of uniaxial and biaxial geogrids were custom-molded using a professional 3D printer. Mechanical properties were measured both on the filament and on the prototype geogrids. The maximum tensile resistance was 6.76 kN/m for the neat-PLA filament and 10.14 kN/m for uniaxial prototype geogrids produced with PLA-based polymer mixed with titanium dioxide. PLA-based materials showed higher tensile properties than polypropylene (PP), the most common petroleum derivative. Conversely, such biomaterials seem to be more brittle and with scarce elongation rate respect PP. Nonetheless, these results are encouraging and can support the use of PLA-based materials for innovative biodegradable geosynthetics production, especially if used in combination with live plants.

Biocomposite Fabrication from Enzymatically Treated Nanocellulosic Fibers and Recycled Polylactic Acid

Recycled polylactic acid (PLAr) was reinforced with treated nanocellulosic hemp fibers for biocomposite fabrication. Cellulosic fibers were extracted from hemp fibers chemically and treated enzymatically. Treated nanocellulosic fibers (NCF) were analyzed by Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Biocomposite fabrication was done with PLAr and three concentrations of treated NCF (0.1%, 0.25%, and 1% (v/v)) and then studied for thermal stability and mechanical properties. Increased thermal stability was observed with increasing NCF concentrations. The highest value for Young’s modulus was for PLAr + 0.25% (v/v) NCF (250.28 ± 5.47 MPa), which was significantly increased compared to PLAr (p = 0.022). There was a significant decrease in the tensile stress at break point for PLAr + 0.25% (v/v) NCF and PLAr + 1% (v/v) NCF as compared to control (p = 0.006 and 0.002, respectively). No significant difference was observed between treatments for tensile stress at yield.

Hybrid and Nonhybrid Laminate Composites of Sugar Palm and Glass Fibre-Reinforced Polypropylene: Effect of Alkali and Sodium Bicarbonate Treatments

In recent years, the hybrid composites of cellulosic and synthetic fibres are tailored to yield materials with reduced cost and weight. Prior to the fabrication of the hybrid composite, in most case, the cellulosic fibre needs surface modification for proper bonding. Therefore, this study investigates the effect of sodium bicarbonate treatment on the physical and mechanical properties of the hybrid and nonhybrid laminate composites of sugar palm and glass fibre-reinforced polypropylene. The findings will be compared with the conventional alkali treatment. The laminate composites were fabricated using the film stacking technique and hot compression process. Prior to the fabrication process, the sugar palm fibre in it which is naturally woven mat was treated with 4 wt% and 10 wt% alkali and sodium bicarbonate, respectively. All the laminate composites were investigated by tensile, flexural, and impact test, water absorption, and morphological examination. The tensile strength increased with both alkaline and sodium bicarbonate treatments for the hybrid and nonhybrid composites. The increase was more pronounced with the alkaline-treated SPF composite (L03) which displayed the highest value of 61.75 MPa, while that of the sodium bicarbonate-treated SPF composite (L04) recorded 58.76 MPa against 53.01 MPa for the untreated SPF composite (L02). The same trend was observed for the flexural strength. In overall, the alkaline treatment yielded better performance in comparison with sodium bicarbonate treatment.