Wood/polymer/nanoclay composites, environmentally friendly sustainable technology: A review

Stronger Together. Poly(Styrene) Gels Reinforced by Soft Gellan Gum

This study targets the synthesis of novel semi-interpenetrating networks and amphiphilic conetworks, where hydrophilic soft matter (Gellan Gum, GG) was combined with hydrophobic rigid poly(styrene), PSt. To achieve that, GG was chemically modified with 4-vinyl benzyl chloride to form a reactive macromonomer with multiple double bonds. These double bonds were used in a copolymerization with styrene to initially form semi-interpenetrating networks (SIPNs) where linear PSt was intertwined within the GG-PSt conetwork. The interpenetrating linear PSt and unreacted styrene were extracted over 3 consecutive days with yields 18–24%. After the extraction, the resulting conetworks (yields 76–82%) were able to swell both in organic and aqueous media. Thermo-mechanical tests (thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis) and rheology indicated that both SIPNs and conteworks had, in most cases, improved thermal and mechanical properties compared to pure poly(styrene) and pure GG gels. This crosslinking strategy proved that the reactive combination of a synthetic polymer and a bio-derived constituent would result in the formation of more sustainable materials with improved thermo-mechanical properties. The binding ability of the amphiphilic conetworks towards several organic dyes was high, showing that they could be used as potential materials in environmental clean-up.

Reactive Cellu-mers-A Novel Approach to Improved Cellulose/Polymer Composites

In this paper, we describe a novel method for preparation of polymer composites with homogeneous dispersion of natural fibers in the polymer matrix. In our approach, Williamson ether synthesis is used to chemically modify cellulose with polymerizable styrene moieties and transform it into a novel multifunctional cellu-mer that can be further crosslinked by copolymerization with styrene. Reactions with model compounds (cellobiose and cellotriose) successfully confirm the viability of the new strategy. The same approach is used to transform commercially available cellulose nanofibrils (CNFs) of various sizes: Sigmacell and Technocell™ 40, 90 and 150. The styrene-functionalized cellulose oligomers and CNFs are then mixed with styrene and copolymerized in bulk at 65 °C with 2,2'-azobisisobutyronitrile as initiator. The resulting composites are in a form of semi-interpenetrating networks (s-IPN), where poly(styrene) chains are either crosslinked with the uniformly dispersed cellulosic component or entangled through the network. Non-crosslinked poly(styrene) (31-41 w%) is extracted with CHCl3 and analyzed by size-exclusion chromatography to estimate the extent of homopolymerization and reveal the mechanism of the whole process. Electron microscopy analyses of the networks show the lack of cellu-mer agglomeration throughout the polymer matrix. The homogeneous distribution of cellulose entities leads to improved thermal and mechanical properties of the poly(styrene) composites compared to the physical mixtures of the same components and linear poly(styrene) of similar molecular mass.

Hybridization of MMT/Lignocellulosic Fiber Reinforced Polymer Nanocomposites for Structural Applications: A Review

In the recent past, significant research effort has been dedicated to examining the usage of nanomaterials hybridized with lignocellulosic fibers as reinforcement in the fabrication of polymer nanocomposites. The introduction of nanoparticles like montmorillonite (MMT) nanoclay was found to increase the strength, modulus of elasticity and stiffness of composites and provide thermal stability. The resulting composite materials has figured prominently in research and development efforts devoted to nanocomposites and are often used as strengthening agents, especially for structural applications. The distinct properties of MMT, namely its hydrophilicity, as well as high strength, high aspect ratio and high modulus, aids in the dispersion of this inorganic crystalline layer in water-soluble polymers. The ability of MMT nanoclay to intercalate into the interlayer space of monomers and polymers is used, followed by the exfoliation of filler particles into monolayers of nanoscale particles. The present review article intends to provide a general overview of the features of the structure, chemical composition, and properties of MMT nanoclay and lignocellulosic fibers. Some of the techniques used for obtaining polymer nanocomposites based on lignocellulosic fibers and MMT nanoclay are described: (i) conventional, (ii) intercalation, (iii) melt intercalation, and (iv) in situ polymerization methods. This review also comprehensively discusses the mechanical, thermal, and flame retardancy properties of MMT-based polymer nanocomposites. The valuable properties of MMT nanoclay and lignocellulose fibers allow us to expand the possibilities of using polymer nanocomposites in various advanced industrial applications.

Potential use of waste from tree pruning and recovered plastic to obtain a building material: Case study of Merida, Mexico

This work presents a study on the use of wood and plastic wastes generated in abundance in Merida, Mexico, to help to reduce them in order to mitigate environmental deterioration. The use of these wastes is proposed to obtain a low-cost building material. So, the escalation process (i.e., extrusion) at the pilot level to obtain a prototype of a wood-plastic composite (WPC) corrugated sheet to evaluate the technical feasibility to make a low-cost product is reported. A corrugated sheet with recycled high-density polyethylene (R-HDPE) was produced. The R-HDPE was collected from Merida's Separation Plant. The wood came from the trimmings of different varieties of trees and shrubs that are periodically pruned. WPC sheets with virgin HDPE were prepared to assess its effect on the materials' mechanical performance. The wood/HDPE weight ratio was 40/60. The performance of the WPC sheets was compared with that of commercial products with similar characteristics, namely acrylic and polyester sheets reinforced with fibreglass, and black asphalt-saturated cardboard sheets. Thus, the effect of natural weathering on the maximum tensile tearing force and on the maximum flexural load of the different types of sheets was evaluated. Although the mechanical performance of the WPC sheets was lower than that of the acrylic and polyacrylic sheets, their performance was much better than that of the cheap black asphalt-saturated cardboard sheets. So, they are a good option to be used as low-cost temporary roofing.

Calcium-Based Sustainable Chemical Technologies for Total Carbon Recycling

Calcium carbide, a stable solid compound composed of two atoms of carbon and one of calcium, has proven its effectiveness in chemical synthesis, due to the safety and convenience of handling the C≡C acetylenic units. The areas of CaC₂ application are very diverse, and the development of calcium-mediated approaches resolves several important challenges. This Review aims to discuss the laboratory chemistry of calcium carbide, and to go beyond its frontiers to organic synthesis, life sciences, materials and construction, carbon dioxide capturing, alloy manufacturing, and agriculture. The recyclability of calcium carbide and the availability of large-scale industrial production facilities, as well as the future possibility of fossil-resource-independent manufacturing, position this compound as a key chemical platform for sustainable development. Easy regeneration and reuse of the carbide highlight calcium-based sustainable chemical technologies as promising instruments for total carbon recycling.

Effect of Surface Modification of Palygorskite on the Properties of Polypropylene/Polypropylene-g-Maleic Anhydride/Palygorskite Nanocomposites

The effect of surface modification of palygorskite (Pal) on filler dispersion and on the mechanical and thermal properties of polypropylene (PP)/polypropylene grafted maleic anhydride (PP-g-MAH)/palygorskite (Pal) nanocomposites was evaluated. A natural Pal mineral was purified and individually surface modified with hexadecyl tributyl phosphonium bromide and (3-Aminopropyl)trimethoxysilane; the pristine and modified Pals were melt-compounded with PP to produce nanocomposites using PP-g-MAH as compatibilizer. The grafting of Pal surface was verified by FT-IR and the change in surface hydrophilicity was estimated by the contact angle of sessile drops of ethylene glycol on Pal tablets. The extent of Pal dispersion and the degree of improvement in both the mechanical and thermal properties were related to the surface treatment of Pal. Modified Pals were better dispersed during melt processing and improved Young’s modulus and strength; however, maximum deformation tended to decrease. The thermal stability of PP/PP-g-MAH/Pal nanocomposites was considerably improved with the content of modified Pals. The degree of crystallinity increased with Pal content, regardless of the surface modification. Surfactant modified Pal exhibited better results in comparison with silane Pal; it is possible that longer alkyl chains from surfactant molecules promoted interactions with polymer chains, thereby improving nanofiller dispersion and enhancing the properties.

Poly(vinyl alcohol)/cellulose nanofibril hybrid aerogels with an aligned microtubular porous structure and their composites with polydimethylsiloxane

Superhydrophobic poly(vinyl alcohol) (PVA)/cellulose nanofibril (CNF) aerogels with a unidirectionally aligned microtubular porous structure were prepared using a unidirectional freeze-drying process, followed by the thermal chemical vapor deposition of methyltrichlorosilane. The silanized aerogels were characterized using various techniques including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and contact angle measurements. The structure of the aerogels fully filled with polydimethylsiloxane (PDMS) was confirmed by SEM and optical microscopy. The mechanical properties of the resulting PDMS/aerogel composites were examined using both compressive and tensile tests. The compressive and tensile Young's moduli of the fully filled PDMS/aerogel composites were more than 2-fold and 15-fold higher than those of pure PDMS. This study provides a novel alternative approach for preparing high performance polymer nanocomposites with a bicontinuous structure.

Cytotoxicity and mutagenicity assessment of organomodified clays potentially used in food packaging

Modern food packaging has made great advances as result of global trends and consumer preferences, which are oriented to obtain improved food quality and safety. In this regard, clay minerals, and mainly Montmorillonite (Mt) are attracting considerable interest in food packaging because of the improvements developed in mechanical and barrier properties. Hence, the present work aim to assess the toxicity of four Montmorillonite-based clay minerals, an unmodified clay, Cloisite®Na+ (CNa+), and three modified Mt clays: Cloisite®30B (C30B), a commercial clay, and Clay1 and Clay2, two novel modified organoclays developed by the Packaging, Transport, & Logistics Research Institute (ITENE). First, the cytotoxic effects were studied in the Human Umbilical Vein Endothelial Cells (HUVEC). In addition, the potential mutagenicity of the clays was evaluated by the Ames test. Clay1 did not induce any cytotoxic effects in HUVEC, although it exhibited potential mutagenicity in TA98 Salmonella typhimurium strain. In contrast, Clay2 produced cytotoxicity in endothelial cells but no mutagenicity was recorded. However, CNa+ was not cytotoxic neither mutagenic. And finally, C30B showed positive results in both assays. Therefore, results showed that clay minerals have a different toxicity profile and a case by case toxicity evaluation is required.

Toxic effects of a modified montmorillonite clay on the human intestinal cell line Caco-2

The incorporation of the natural mineral clay montmorillonite into polymeric systems enhances their barrier properties as well as their thermal and mechanical resistance, making them suitable for a wide range of industrial applications, e.g., in the food industry. Considering humans could easily be exposed to these clays due to migration into food, toxicological and health effects of clay exposure should be studied. In the present work, the cytotoxic effects induced by two different clays (the unmodified clay Cloisite(®) Na(+) , and the organically modified Cloisite(®) 30B) on Caco-2 cells were studied after 24 and 48 h of exposure. The basal cytotoxicity endpoints assessed were total protein content, neutral red uptake and a tetrazolium salt reduction. Our results showed that only Cloisite(®) 30B induced toxic effects. Therefore, the effects of subcytotoxic concentrations of this clay on the generation of intracellular reactive oxygen species, glutathione content and DNA damage (comet assay) were investigated. Results indicate that oxidative stress may be implicated in the toxicity induced by Closite(®) 30B, in regards of the increases in intracellular reactive oxygen species production and glutathione content at the highest concentration assayed, while no damage was observed in DNA. The most remarkable morphological alterations observed were dilated cisternae edge in the Golgi apparatus and nucleolar segregation, suggesting impairment in the secretory functions, which could be related to inhibition in the synthesis of proteins.