Towards more sustainable material formulations: a comparative assessment of PA11-SGW flexural performance versus oil-based composites

The replacement of commodity polyolefin, reinforced with glass fiber (GF), by greener alternatives has been a topic of research in recent years. Cellulose fibers have shown, under certain conditions, enough tensile capacities to replace GF, achieving competitive mechanical properties. However, if the objective is the production of environmentally friendlier composites, it is necessary to replace oil-derived polymer matrices by bio-based or biodegradable ones, depending on the application. Polyamide 11 (PA11) is a totally bio-based polyamide that can be reinforced with cellulosic fibers. Composites based on this polymer have demonstrated enough tensile strength, as well as stiffness, to replace GF-reinforced polypropylene (PP). However, flexural properties are of high interest for engineering applications. Due to the specific character of short-fiber-reinforced composites, significant differences are expected between the tensile and flexural properties. These differences encourage the study of the flexural properties of a material prior to the design or development of a new product. Despite the importance of the flexural strength, there are few works devoted to its study in the case of PA11-based composites. In this work, an in-depth study of the flexural strength of PA11 composites, reinforced with Stoneground wood (SGW) from softwood, is presented. Additionally, the results are compared with those of PP-based composites. The results showed that the SGW fibers had lower strengthening capacity reinforcing PA11 than PP. Moreover, the flexural strength of PA11-SGW composites was similar to that of PP-GF compositesPostprint (published version

Bacterial Cellulose Network from Kombucha Fermentation Impregnated with Emulsion-Polymerized Poly(methyl methacrylate) to Form Nanocomposite

The use of bio-based residues is one of the key indicators towards sustainable development goals. In this work, bacterial cellulose, a residue from the fermentation of kombucha tea, was tested as a reinforcing nanofiber network in an emulsion-polymerized poly(methyl methacrylate) (PMMA) matrix. The use of the nanofiber network is facilitating the formation of nanocomposites with well-dispersed nanofibers without using organic solvents or expensive methodologies. Moreover, the bacterial cellulose network structure can serve as a template for the emulsion polymerization of PMMA. The morphology, size, crystallinity, water uptake, and mechanical properties of the kombucha bacterial cellulose (KBC) network were studied. The results showed that KBC nanofibril diameters were ranging between 20-40 nm and the KBC was highly crystalline, >90%. The 3D network was lightweight and porous material, having a density of only 0.014 g/cm(3). Furthermore, the compressed KBC network had very good mechanical properties, the E-modulus was 8 GPa, and the tensile strength was 172 MPa. The prepared nanocomposites with a KBC concentration of 8 wt.% were translucent with uniform structure confirmed with scanning electron microscopy study, and furthermore, the KBC network was homogeneously impregnated with the PMMA matrix. The mechanical testing of the nanocomposite showed high stiffness compared to the neat PMMA. A simple simulation of the tensile strength was used to understand the limited strain and strength given by the bacterial cellulose network. The excellent properties of the final material demonstrate the capability of a residue of kombucha fermentation as an excellent nanofiber template for use in polymer nanocomposites

Life cycle assessment of PE and PP multi film compared with PLA and PLA reinforced with nanoclays film

Plastic has become essential for our economy and the packaging industry. However, plastic use is linked to environmental problems such as waste generation and loss of resources, since only 42% of the plastic used for packaging purposes is recycled. Another problem associated with the use of plastic materials is caused by their abandonment in the environment since they are non-degradable polymers. This paper analyses the environmental performance of using biodegradable poly-lactic acid bags, pure (PLA) and reinforced with nanoclays (PLA + NC), in comparison to conventional alternatives made of polyethylene (PE) and polypropylene (PP) for being used to pack fresh bakery products. The results reveal that for Climate Change and Fossil Resources use, PLA + NC performs better than the alternatives. In the case of Climate Change, it has 45% less impact than low density polyethylene (LDPE), 39% less than PP, and 2% less than PLA. However, the use of PLA + NC, results in higher impacts on Land Use and Water Use, because this is produced from crops. Compared with PLA, PLA + NC has 5% less impact on these impact categories, but between 99 and 100% more impact on Land Use and between 79 and 81% more impact on Water use than PP and LDPE. Thus, poly-lactic acid bags reinforced with nanoclays are shown as an alternative for fossil-based polymers (PE and PP) for certainty type of applications when we focus on Climate Change and Fossil resources use reduction. In this sense, the results also reveal that the most environmentally friendly end-of-life for PLA and PLA + NC is incineration instead of composting.Peer ReviewedPostprint (published version

Maleic anhydride polylactic acid coupling agent prepared from solvent reaction: synthesis, characterization and composite performance

In the present work, a functionalization of polylactic acid (PLA) has been carried out to anchor maleic anhydride onto the main polymer chain to promote improvement in the compatibility of this polymer matrix with cellulose fibres. Low-molecular-weight PLA has been reacted with maleic anhydride following different procedures: a bulk reaction in an internal mixer and a solution reaction. The presence of oxygen during bulk processing did not allow for functionalization, guiding the reaction towards a decrease in the molecular weight of the material. On the contrary, a controlled reaction under an inert atmosphere in the presence of dioxane as the solvent, at reflux temperature, led to the functionalization of the polymer reaching different yields depending on the percentage of radical initiator and maleic anhydride added and reaction time. The yield of functionalization has been monitored by acid number titration as well as 1H NMR, with optimal yield values of functionalization being up to 3.5%. The PLA-functionalized formula has been used to make commercial PLA compatible with cellulose fibres derived from a thermomechanical treatment. The addition of 10% w/w of fibres to PLA increases the ultimate tensile strength (UTS) of PLA by up to 15%. The incorporation of 4 w/w of the already-functionalized coupling agent to the composite produces improvements in UTS of up to 24% regarding PLA, which confirms the functionalization from a performance point of view.Peer ReviewedPostprint (published version

Simulated environmental conditioning of PHB composites reinforced with barley fibres to determine the viability of their use as plastics for the agriculture sector

Nowadays, the search for new materials with a sustainable character to reduce the production of residues is under continuous research. In this sense, fully biodegradable composites based on polyhydroxybutyrate and different pretreated fibres coming from barley straw have been fabricated, and their resistance to environmental controlled conditions have been characterized. The materials were already compounded in a kinetic mixer and injection-moulded as specimens for tensile assay to be aged in a Xenotest chamber so as to simulate environmental conditioning. The samples, after accelerated aging, were characterized thus: mechanical characterization (tensile assay), water uptake (immersion and contact angle), and surface observation (optical and SEM microscopy). The incorporation of the fibres helps the composite to keep its structure for a longer time. On the other hand, the presence of the fibres increases the water uptake capacity to allow water permeation in the composite, which allows final degradation, characterised by a significant drop in properties after one month of exposure to simulated environmental conditions.Peer ReviewedPostprint (published version

Nanoclay effect into the biodegradation and processability of poly(lactic acid) nanocomposites for food packaging

One of the most promising expectations in the design of new materials for food packaging is focused on the development of biodegradable systems with improved barrier character. In this sense PLA reinforced with nanoclay is a potential alternative to the use of conventional oil-derivative polymers due to the synergetic effect of the biodegradable character of PLA and the barrier-induced effect derived from the dispersion of nanoparticles. In this work, composite materials based on PLA and reinforced with bentonite nanoparticles (up to 4% w/w) (NC) have been prepared to produce films with improved barrier character against water vapor transportation. Additionally, the biodegradable character of the composites depending on the crystallinity of the polymer and percentage of NC have been evaluated in the presence of an enzymatic active medium (proteinase K). Finally, a study of the capacity to film production of the composites has been performed to determine the viability of the proposals. The dispersion of the nanoparticles induced a tortuous pathway of water vapor crossing, reducing this diffusion by more than 22%. Moreover, the nanoclays materials were in all the cases acceptable for food packing in terms of migration. A migration lower than 1 mg/m2 was obtained in all the materials. Nonetheless, the presence of the nanoclays in decreased biodegradable capacity was observed. The time was enlarged to more than 15 days for the maximum content (4% w/w). On the other hand, the incorporation of NC does not avoid the processability of the material to obtain film-shaped processed materials.Postprint (published version

Valorization Strategy for Leather Waste as Filler for High-Density Polyethylene Composites: Analysis of the Thermal Stability, Insulation Properties and Chromium Leaching.

Leather waste (BF) and high-density polyethylene (HDPE) were compounded in a lab scale internal mixer and processed by means of injection molding. In this study, leather waste and HDPE composites were characterized by instrumental techniques such as differential scanning calorimetry (DSC), thermo-gravimetric Analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). Physical integrity of composites against chemical exposure and chromium-leaching properties of the composites were also investigated. This study shows that the incorporation of 30% leather waste fiber into HDPE composites decreases the thermal conductivity of the composite samples by 17% in comparison to that of neat HDPE samples. Composites showed no thermal degradation during processing cycle. Strong interfacial bonding between leather waste and polymer results in comparable low-leachate levels to maximum allowed concentration for nonhazardous waste, and good chemical resistance properties. The BF/HDPE composites could be a promising low-cost alternative in industrial application areas of HDPE, where high-mechanical strength and low-thermal conductivity is required.This research was funded by the Spanish Ministry of Science and Innovation, project KAIROS-BIOCIR (PID2019-104925RB-C32

Evaluation of thermal and thermomechanical behaviour of bio-based polyamide 11 based composites reinforced with lignocellulosic fibres

In this work, polyamide 11 (PA11) and stone ground wood fibres (SGW) were used, as an alternative to non-bio-based polymer matrices and reinforcements, to obtain short fibre reinforced composites. The impact of the reinforcement on the thermal degradation, thermal transitions and microstructure of PA11-based composites were studied. Natural fibres have lower degradation temperatures than PA11, thus, composites showed lower onset degradation temperatures than PA11, as well. The thermal transition and the semi-crystalline structure of the composites were similar to PA11. On the other hand, when SGW was submitted to an annealing treatment, the composites prepared with these fibres increased its crystallinity, with increasing fibre contents, compared to PA11. The differences between the glass transition temperatures of annealed and untreated composites decreased with the fibre contents. Thus, the fibres had a higher impact in the composites mechanical behaviour than on the mobility of the amorphous phase. The crystalline structure of PA11 and PA11-SGW composites, after annealing, was transformed to ’ more stable phase, without any negative impact on the properties of the fibresPostprint (published version

Study of the flexural modulus of lignocellulosic fibers reinforced bio-based polyamide11 green composites

The stiffness of a material has high impact when its industrial use is considered. Moreover, this property has interest in the case of short fiber reinforced materials due to its dependence on the orientation of the fibers against the loads. Due to nowadays-environmental concerns, greener alternatives to oil-based composites are under study and development showing some promising results. In this work, a polyamide 11 reinforced with lignocellulosic fiber composite is evaluated as such sustainable alternative. Previous works showed the suitability of PA11-based composites to replace glass fiber reinforced polypropylene. Nonetheless, there is a lack of information about the flexural modulus behavior of these composites. This is of interest because, under some conditions, flexural modulus is more representative of a material behavior than Young's modulus. The flexural moduli of these composites were analyzed under a three point bending test and the results were evaluated from macro and micromechanical points of view. The increment of the modulus with the fiber contents implied a good dispersion of the reinforcements. Nonetheless, the results were lower than those observed for the tensile modulus. This was unexpected due to the anisotropy of the bending test. The micromechanics analysis showed a lower performance of the fiber during the flexural test. These lower results were related with a non-optimal interface or with the non-adequate compression of the fibers. Additionally, the calculus of the void volume showed low void contentsPostprint (published version

Valorization strategy for leather waste as filler for high-density polyethylene composites: analysis of the thermal stability, insulation properties and chromium leaching

Leather waste (BF) and high-density polyethylene (HDPE) were compounded in a lab scale internal mixer and processed by means of injection molding. In this study, leather waste and HDPE composites were characterized by instrumental techniques such as differential scanning calorimetry (DSC), thermo-gravimetric Analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). Physical integrity of composites against chemical exposure and chromium-leaching properties of the composites were also investigated. This study shows that the incorporation of 30% leather waste fiber into HDPE composites decreases the thermal conductivity of the composite samples by 17% in comparison to that of neat HDPE samples. Composites showed no thermal degradation during processing cycle. Strong interfacial bonding between leather waste and polymer results in comparable low-leachate levels to maximum allowed concentration for nonhazardous waste, and good chemical resistance properties. The BF/HDPE composites could be a promising low-cost alternative in industrial application areas of HDPE, where high-mechanical strength and low-thermal conductivity is required.This research was funded by the Spanish Ministry of Science and Innovation, project KAIROS-BIOCIR (PID2019-104925RB-C32).Peer ReviewedPostprint (published version