Review Articles

It is critical to develop sustainable, effective, and innovative technologies for society, particularly for processing of biomass, so that the green/ sustainable advantages can be extended to the final products. This review examined two-step biological-mechanical defiberization of lignocellulosic biomass to produce fibers. Two biological pretreatment methods of fungi and enzymes were mainly introduced, with particular focus on the energy consumption. Potential application methods, advantages, disadvantages, process economics, and future prospects of two biological pretreatment methods were considered to derive a complete road map for the proposed process. With the help of biological pretreatment, the mechanical pulping production could not only improve the paper strength, but also decrease energy consumption at about 40%. This process fits well with the green/sustainable strategy to produce lignocellulosic fibers with reasonable quality while having minimal environmental impact.

In the past decade, the Chinese paper industry, which is highly polluting and energy intensive, has shown overall increases in production, sales, income, and profit, although the growth rate has declined. Overall, China’s paper industry exhibits small-scale and scattered distribution, characterized by continuous overcapacity and outdated technical knowledge. This has inevitably resulted in a variety of serious environmental problems during its development. Owing to the environmental problems resulting from the development of the paper industry, various environmental regulatory policies and measures have been adopted in China, mainly command-and-control, market-based, and voluntary policies and measures. This study identifies and analyzes particular issues inherent to China’s environmental regulatory policies and measures regarding the paper industry and proposed policy suggestions for improving the environmental regulation of China’s paper industry.

The color, texture, and natural defects of wood are important factors affecting its commercial value. Change of wood’s surface color is a primary way to improve its value. This study analyzes and summarizes the development status and existing problems of the traditional wood dyeing process and induced discoloration process. It is proposed that color improvement with photonic crystal structure color is a clean and pollution-free ecological biomimetic coloring technology. Its research status in the fields of fiber, fabric, wood, wood-based panel surface color improvement, new coatings for wood, and lignocellulose nanocrystalline structure color film are reviewed. The following aspects were studied: 1) construction and mechanistic study of the wood surface structure color film, 2) light response and interface mechanistic study of the wood surface structure color film, 3) large-scale application technology study of the wood surface biomimetic structure color film, and 4) preparation and functional development of structural color films of lignocellulose nanocrystal.

Oil palm biomass is readily available in Malaysia. However, its high lignin content makes it undesirable for further processing. Pretreatment is employed to reduce the amount of lignin. Many resources exist on pretreatment methods for lignocellulosic biomass, but there are few articles specifically on oil palm biomass. Therefore, this review focuses on pretreatment methods for oil palm biomass, comparing their main strengths and limitations. Furthermore, this review tabulates different pretreatment conditions utilized, combinations of pretreatment methods, the resulting yields, and the potential applicability in producing value-added products. Because the main limitation of pretreatment is the formation of toxic compounds such as furfural and hydroxymethylfurfural, this review also discusses chemical detoxification methods for oil palm biomass residues. According to this review, among all types of oil palm biomass, oil palm empty fruit brunch is the most widely studied, and alkaline pretreatment is the most popular of all pretreatment methods. Combination of pretreatment methods is suitable for biomass with greater lignin content, to increase delignification efficiency. Furthermore, a combination of overliming and activated carbon treatment removes the maximum amount of toxic by-products.

This review considers three aspects of the weathering of wood – natural weathering, accelerated weathering, and simulated weathering. Natural weathering begins when unprotected wood, such as an unpainted board, is exposed to cycles of solar radiation and rain. Unpainted barns and fenceposts take on a gray coloration and their surfaces may become rough, loosened, or checked with the passage of time. The underlying causes of such changes involve ultraviolet light, the effects of cyclic wetting and drying, and the action of certain fungi. Accelerated weathering tests have been used not only to evaluate the effectiveness of varnishes and paints, but also to aid in the understanding of factors affecting natural weathering. Simulated weathering usually has the goal of quickly and conveniently changing the appearance of fresh wood to give the impression of weathering. This might increase its appeal for various decorative purposes. Information about simulated weathering, though largely absent from the scientific literature, is very much alive in social media. This article considers the science behind all three types of weathering in the light of published accounts.

Lignocellulosic biomass is a class of sustainable material that can be utilized as a raw feedstock in biofuel and chemical production. However, the complex matrix structure of lignocellulosic materials complicates conversion processes, such as enzymatic hydrolysis. Therefore, an efficient pretreatment process is required to disrupt the plant cell wall structure and maximize the recovery of valuable soluble components from lignocellulosic biomass during hydrolysis. In addition, an effective pretreatment method should use the minimum necessary amounts of energy and chemicals to minimize the cost of the end product. Further, it should reduce the formation of inhibitory compounds that affect enzymes and microorganisms during hydrolysis and fermentation, and it should be applicable to a wide variety of feedstocks. The research presented in this review has highlighted the pros and cons of the current technologies employed in pretreatment processes. Further study should be done to optimize and improve these technologies to enhance the efficiency of the production of biofuels and other valuable components.

Cocoa is among the most cultivated and important tropical crops in the world, and it is economically viable in the agro-pastoral systems of tropical Africa. Further, the amount of cocoa residue is steadily increasing due to the strong worldwide demand for chocolate products. This review of cocoa residue found that an average of 18 publications per year were published in the last 10 years. The most common type of publication on cocoa pod husks (CPH) was newspaper articles, which comprised 50% of the publications. This review examines the use of CHP in sustainable development, agrochemical materials, and agro-materials through their potential valorizations into high value-added products. Indeed, CPH is an abundant, accessible, and renewable resource of bioproducts, dietary fibers, nutraceuticals, functional foods, pectin, antioxidant compounds, theobromine, and minerals. Potential food applications of CPH include the production of flavor compounds, gums, texturing agents, and others. The production of biomaterials for food and non-food use, biofuels, and organic acids, such as lactic acid (the polymerization of which produces the PLA used in bioplastic production), are several potential areas for the biotechnological development of CPH and its fractions.

Society’s wish list for future packaging systems is placing some daunting challenges upon researchers: In addition to protecting contents during storage and shipping, the material must not bio-accumulate, and it should be readily recyclable by using practical processing steps. This article considers strategies employing bio-based plastics and reviews published information relative to their performance. Though bioplastics such as poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB) can be prepared from plant materials, their default properties are generally inferior to those of popular synthetic plastics. In addition, some bioplastics are not easily decomposed in soil or seawater, and the polymers can undergo chemical breakdown during recycling. This review considers strategies to overcome such challenges, including the use of biodegradable cellulose-based reinforcing particles. In addition to contributing to strength, the cellulose can swell the bioplastic, allowing enzymatic attack. The rate-controlling step in bioplastic degradation also can be abiotic, i.e. not involving enzymes. Though there is much more work to be done, much progress has been achieved in formulating bioplastic composites that are biodegradable, recyclable, and higher in strength compared to the neat polymer. Emphasis in this review is placed on PLA and PHB, but not to the exclusion of other bioplastic matrix materials.

This effort is focused on work completed publicly and privately within academic research and industrial sectors on the utilization of lignin to produce thermosets, thermoplastics, foams, hydrogels, and rubbers. The size of the plastics market and the current and projected influence of lignin on it were evaluated. Further, an analysis of patent activity was employed to show the direction of and interest for lignin in these markets. The market trends documented in the literature, when coupled with detailed patent research, offer a new approach to evaluate potential markets and future directions. The analysis of the commercial market sizes of bioplastics and segmentation showed low penetration of actual lignin-based bioplastics. This exposed the contradiction between the abundance of technologies for lignin-based materials and their little practical use. In addition, this finding highlighted a severe gap between lignin research and development and the actual market.

Liquid crystals (LC) have been found to have many unique characteristics during the last few decades. The liquid crystal phase is ubiquitous in the biological world, as well as in cellulose and its derivatives. Cellulose nanocrystals (CNC), which can obtain the chiral LC phase in aqueous suspension, have been attracting much attention. The unique size and properties of CNC, such as their light weight, special optical properties, non-toxicity, and biocompatibility, etc., have made them widely applicable in diverse fields. This brief literature review introduces the relationship between the LC phase and CNC. Advantages of CNC as a liquid crystal forming material and the preparation of CNC are discussed. The left-handed cholesteric phase structure and the corresponding unique optical properties of CNC-based LC are described in detail. The CNC-based LC aqueous suspension and three stages of forming LC phase are also described. Then, the main reasons accounting for the brittleness and non-uniformity of pristine CNC-based LC are summarized, as well as ways to overcome these problems. Finally, some optical applications of CNC-based LC films in anti-counterfeiting, colorimetric sensors, and composite devices are considered.