Cellulose-Reinforced Polylactic Acid Composites for Three-Dimensional Printing Using Polyethylene Glycol as an Additive: A Comprehensive Review.

Growing concerns about environmental issues and global warming have garnered increased attention in recent decades. Consequently, the use of materials sourced from renewable and biodegradable origins, produced sustainably, has piqued the interest of scientific researchers. Biodegradable and naturally derived polymers, such as cellulose and polylactic acid (PLA), have consistently been the focus of scientific investigation. The objective is to develop novel materials that could potentially replace conventional petroleum-based polymers, offering specific properties tailored for diverse applications while upholding principles of sustainability and technology as well as economic viability. Against this backdrop, the aim of this review is to provide a comprehensive overview of recent advancements in research concerning the use of polylactic acid (PLA) and the incorporation of cellulose as a reinforcing agent within this polymeric matrix, alongside the application of 3D printing technology. Additionally, a pivotal additive in the combination of PLA and cellulose, polyethylene glycol (PEG), is explored. A systematic review of the existing literature related to the combination of these materials (PLA, cellulose, and PEG) and 3D printing was conducted using the Web of Science and Scopus databases. The outcomes of this search are presented through a comparative analysis of diverse studies, encompassing aspects such as the scale and cellulose amount added into the PLA matrix, modifications applied to cellulose surfaces, the incorporation of additives or compatibilizing agents, variations in molecular weight and in the quantity of PEG introduced into the PLA/cellulose (nano)composites, and the resulting impact of these variables on the properties of these materials.

Effect of Spent Coffee Grounds on the Crystallinity and Viscoelastic Behavior of Polylactic Acid Composites.

This work investigated the addition of spent coffee grounds (SCG) as a valuable resource to produce biocomposites based on polylactic acid (PLA). PLA has a positive biodegradation effect but generates poor proprieties, depending on its molecular structure. The PLA and SCG (0, 10, 20 and 30 wt.%) were mixed via twin-screw extrusion and molded by compression to determine the effect of composition on several properties, including mechanical (impact strength), physical (density and porosity), thermal (crystallinity and transition temperature) and rheological (melt and solid state). The PLA crystallinity was found to increase after processing and filler addition (34-70% in the 1st heating) due to a heterogeneous nucleation effect, leading to composites with lower glass transition temperature (1-3 °C) and higher stiffness (~15%). Moreover, the composites had lower density (1.29, 1.24 and 1.16 g/cm3) and toughness (30.2, 26.8 and 19.2 J/m) as the filler content increased, which is associated with the presence of rigid particles and residual extractives from SCG. In the melt state, polymeric chain mobility was enhanced, and composites with a higher filler content became less viscous. Overall, the composite with 20 wt.% SCG provided the most balanced properties being similar to or better than neat PLA but at a lower cost. This composite could be applied not only to replace conventional PLA products, such as packaging and 3D printing, but also to other applications requiring lower density and higher stiffness.

Waste Paper as a Valuable Resource: An Overview of Recent Trends in the Polymeric Composites Field.

This review focuses on polymeric waste-paper composites, including state-of-the-art analysis with quantitative and qualitative discussions. Waste paper is a valuable cellulose-rich material, produced mainly from office paper, newspaper, and paper sludge, which can be recycled and returned to paper production or used in a new life cycle. A systematic literature review found 75 publications on this material over the last 27 years, with half of those published during the last five years. These data represent an increasing trend in the number of publications and citations that have shown an interest in this field. Most of them investigated the physicomechanical properties of composites using different contents of raw waste paper or the treated, modified, and cellulose-extracted types. The results show that polyethylene and polypropylene are the most used matrices, but polylactic acid, a biodegradable/sourced polymer, has the most citations. The scientific relevance of waste-paper composites as a subject includes the increasing trend of the number of publications and citations over the years, as well as the gaps identified by keyword mapping and the qualitative discussion of the papers. Therefore, biopolymers and biobased polymers could be investigated more, as well as novel applications. The environmental impact in terms of stability and degradation should also receive more attention regarding sustainability and life cycle analyses.

Valorization of Spent Coffee Grounds as Precursors for Biopolymers and Composite Production.

Spent coffee grounds (SCG) are a current subject in many works since coffee is the second most consumed beverage worldwide; however, coffee generates a high amount of waste (SCG) and can cause environmental problems if not discarded properly. Therefore, several studies on SCG valorization have been published, highlighting its waste as a valuable resource for different applications, such as biofuel, energy, biopolymer precursors, and composite production. This review provides an overview of the works using SCG as biopolymer precursors and for polymer composite production. SCG are rich in carbohydrates, lipids, proteins, and minerals. In particular, carbohydrates (polysaccharides) can be extracted and fermented to synthesize lactic acid, succinic acid, or polyhydroxyalkanoate (PHA). On the other hand, it is possible to extract the coffee oil and to synthesize PHA from lipids. Moreover, SCG have been successfully used as a filler for composite production using different polymer matrices. The results show the reasonable mechanical, thermal, and rheological properties of SCG to support their applications, from food packaging to the automotive industry.

Effect of different degradation types on properties of plastic waste obtained from espresso coffee capsules.

In terms of large use of plastic products, a necessity exists to minimize effects of the waste produced on environment by recycling, reuse and application in new products. In Brazil, the espresso coffee capsules are an emerging plastic waste, representing 0.9% of the coffee consumed in 2017. Therefore, Nescafé Dolce Gusto espresso coffee capsules were chosen in order to understand the polypropylene stabilization and degradation initiators with the purpose of recycling by applying in a composite material, as home composting product. In this context, the plastic capsule wastes were exposed to chemical, thermal, accelerated weathering (ultraviolet radiation + humidity) and natural weathering in order to analyze the influence of exposure and possibilities of a real application in a composting environment. Masses of the samples were monitored before and during the weathering conditions. Thermal (TGA and DSC) and chemical (FTIR) analysis were carried out before and after exposure. No changes in thermal stability were observed, however, samples conditioned in acid solution presented thermal degradation event beginning at 131 °C. In addition, all samples presented a similar behavior of melting and crystallization points, which did not change with exposure. FTIR analysis showed a disappearance of CC and CO bonds on samples exposed to natural weathering and basic solution conditioning. It also showed formation of chromophores groups on samples exposed to accelerated weathering. The visual analysis showed huge differences in samples exposed to accelerated weathering and acid solution, which were the most damaged. On the other hand, samples exposed to natural weathering, thermal and basic conditioning did not presented significantly changes supported by the TGA and FTIR results.

Obtainment and characterization of nanocellulose from an unwoven industrial textile cotton waste: Effect of acid hydrolysis conditions.

Cellulose nanocrystals (CNCs) have a promising application in many advanced products, such as biomedical applications and hydrogels. In this research, industrial cotton waste was treated using alkali and bleaching to eliminate hemicellulose, lignin, and other amorphous contents. The efficiency of these treatments was proven by chemical compositions analysis, which showed an increase in cellulose percentage with the progression of treatments. Fibers were analyzed by X-ray diffraction, thermogravimetric, and Scanning Electron Microscopy (SEM). CNCs were then prepared by acid hydrolysis using different sulfuric acid concentrations (50 wt%, 60 wt% and 64 wt%) and two reactions time (60 min. and 75 min.) resulting in six CNCs suspensions. CNCs were analyzed by X-ray diffraction, thermogravimetric, zeta potential, and Transmission Electron Microscopy (TEM). CNCs obtained exhibited a good crystallinity index varying from 75 to 81% and thermal stability between 146 °C and 200 °C. TEM analysis showed that sulfuric acid concentration influenced in CNCs length (105 nm-5880 nm). By analyzing all results, the optimal parameters for acid hydrolysis were 64% (w/w) of acid concentration combined with 60 min. of reaction time. The preparation of CNCs in this work showed some prospects of using untraditional industrial cotton waste as an advanced material.

Preparation of nanocellulose from Imperata brasiliensis grass using Taguchi method.

Cellulose nanoparticles (CNs) were prepared by acid hydrolysis of the cellulose pulp extracted from the Brazilian satintail (Imperata Brasiliensis) plant using a conventional and a total chlorine free method. Initially, a statistical design of experiment was carried out using Taguchi orthogonal array to study the hydrolysis parameters, and the main properties (crystallinity, thermal stability, morphology, and sizes) of the nanocellulose. X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), zeta potential and thermogravimetric analysis (TGA) were carried out to characterize the physical-chemical properties of the CNs obtained. Cellulose nanoparticles with diameter ranging from 10 to 60 nm and length between 150 and 250 nm were successfully obtained at sulfuric acid concentration of 64% (m/m), temperature 35 °C, reaction time 75 min, and a 1:20 (g/mL) pulp-to-solution ratio. Under this condition, the Imperata Brasiliensis CNs showed good stability in suspension, crystallinity index of 65%, and a cellulose degradation temperature of about 117 °C. Considering that these properties are similar to those of nanocelluloses from other lignocellulosics feedstocks, Imperata grass seems also to be a suitable source for nanocellulose production.