Review Articles

Because of the impending energy crisis and the environmental problems caused by the excessive use of fossil fuels, biofuels produced from renewable energy biomass have been playing a more significant role in the world. This follows from their obvious environmental and economic advantages. Bioethanol, the most widely used transportation biofuel, is typically derived from plant-based feedstock sources such wheat, sugar beet, corn, straw, and wood. However, the main problem with bioethanol production is that despite the range of feedstock, raw material availability varies considerably from season to season, as there is no systematic framework. By combining technological paradigm theory with literature mining, we found that bioethanol feedstock production development has followed a three-stage trajectory, which is in accordance with the traditional technological paradigm – the S-curve. This new curve can be divided into BFDP (bioethanol feedstock development paradigm) competition, BFDP diffusion, and BFDP shift. Each phase has a different generation of feedstock; first-generation bioethanol in BFDP competition, second-generation bioethanol in BFDP diffusion, and third-generation bioethanol in BFDP shift. Further, based on the technological support, literature mining, and a realistic background, the second-generation bioethanol (mainly lignocellulosic biomass) is expected to continue to be a significant future trend in the world. The new BFDP framework presented in this paper may provide scholars with research ideas for the future.

This paper reviews the published and ongoing research work on kenaf/synthetic and Kevlar®/cellulosic fiber-reinforced composite materials. The combination of natural fibers with synthetic fibers in hybrid composites has become increasingly applied in several different fields of technology and engineering. As a result, a better balance between performance and cost is expected to be achieved by 2015, through appropriate material design. This review is intended to provide an outline of the essential outcomes of those hybrid composite materials currently utilized, focusing on processing and mechanical and structural properties.

The chemical industry is being forced to evaluate new strategies for more effective utilization of renewable feedstocks to diminish the use of fossil resources. In this literature review, the integration of both acidic and alkaline pretreatment phases of hardwood and softwood chips with chemical pulping is discussed. Depending on the pretreatment conditions, high-volume sulfur-free fractions with varying chemical compositions can be produced. In case of acidic pretreatments, the major products include carbohydrates (mono-, oligo-, and polysaccharides), whereas under alkaline (i.e., aqueous NaOH) pretreatment conditions, the sulfur-free fractions of aliphatic carboxylic acids, lignin, and extractives are primarily obtained. All these fractions are potentially interesting groups of compounds and can be used in a number of applications. Finally, the effects of pretreatments on pulping are also considered. Although it is believed that there are important advantages to be gained by integrating this type of renewable raw material-based production, in particular, with kraft pulping, sulfur-free pulping methods such as soda-AQ and oxygen/alkali delignification processes are also briefly discussed.

Contact angle methods are widely used to evaluate the wettability of cellulose-based surfaces and to judge their suitability for different applications. Wettability affects ink receptivity, coating, absorbency, adhesion, and frictional properties. There has been a continuing quest on the part of researchers to quantify the thermodynamic work of adhesion between cellulosic surfaces and various probe liquids and to account for such components of force as the London/van der Waals dispersion force, hydrogen bonding, and acid and base interactions. However, due in part to the rough, porous, and water-swellable nature of cellulosic materials, poor fits between various theories and contact angle data have been observed. Such problems are compounded by inherent weaknesses and challenges of the theoretical approaches that have been employed up to this point. It appears that insufficient consideration has been given to the challenging nature of cellulosic materials from the perspective of attempting to gain accurate information about different contributions to surface free energy. Strong hysteresis effects, with large differences between advancing and receding contact angles, have been overlooked by many researchers in attempting to quantify the work of adhesion. Experimental and conceptual approaches are suggested as potential ways to achieve more reliable and useful results in future wettability studies of cellulosic surfaces.

Anaerobic digestion is a well-established biological process for converting biomass in waste streams into a renewable energy source, and it also contributes to the treatment of these waste streams. In this introductory mini-review, some fundamental aspects of anaerobic digestion for use in the pulp and paper industry and other sectors are briefly summarized. The contents include the basics of anaerobic digestion, feedstocks, key process parameters, and typical anaerobic digesters/reactors and their representative manufactures. Fostering the more efficient and widespread commercial use of anaerobic digestion technologies would be a critical strategy to address the issues of energy, the environment, and sustainability.

This paper presents the results of a structured review of published articles that discuss stakeholders’ perceptions of bioenergy, including both biofuels and biopower. An electronic search process using numerous key terms identified 44 peer-reviewed publications from 2000 to 2013 that focused on stakeholders’ perceptions, understanding, and acceptance of bioenergy. These findings indicate that in the last decade the research community has been more active in publications focused on the societal and public perceptions of the bioenergy industry compared to prior years. Among the reviewed studies, most (84%) are based in the US and Europe, and only a few recent studies have focused on stakeholders in Asia and other parts of the world. This review revealed no standardized methods for evaluation of stakeholder perception, for data collection, or statistical analysis of the data. Among stakeholder groups, the majority of studies focused on the general public or the consumer’s opinion about bioenergy (79% of studies). Overall findings show that the stakeholder groups show low to moderate support for the bioenergy industry. As anticipated, the stakeholder groups had varied views about the opportunities and risks associated with bioenergy industry, and these views varied based on their experiences.

Recent developments in low consistency refining in mechanical pulping have raised questions about the differences between low and high consistency refining. This paper, originally presented to the UBC Energy Reduction in Mechanical Pulping Committee on 10 June 2015 at the PACWEST Conference in Whistler, BC, Canada, discusses the author’s perspectives on these issues as well as on mechanical pulping in general.

Trends in the production and applications of torrefied wood/biomass are reviewed in this article. The thermochemical conversion of biomass is a promising technology because biomass is an environmentally friendly fuel that produces substantially lower CO2 emissions compared to fossil fuel. Torrefaction is the thermal treatment of biomass at temperatures from 200 to 300 ˚C in the absence of air or oxygen to liberate water and release volatile organic compounds, primarily through the decomposition of the hemicelluloses. Torrefied biomass has a higher heating value, is more hydrophobic, resists rotting, and has a prolonged storage time. The different torrefaction technologies and reactors are described. An overview of the applications of torrefied biomass, the economic status, and future prospects of torrefaction technology are presented and discussed. Currently, torrefaction demonstration plants have technical problems that have delayed their commercial operation. Torrefaction reactors still require optimization to economically meet end-use requirements and attain product standardization for the market. Several characteristics of torrefaction need to be demonstrated or scaled up for successful commercialization.

The prospects of biofuel production from microalgal carbohydrates and lipids coupled with greenhouse gas mitigation due to photosynthetic assimilation of CO2 have ushered in a renewed interest in algal feedstock. Furthermore, microalgae (including cyanobacteria) have become established as commercial sources of value-added biochemicals such as polyunsaturated fatty acids and carotenoid pigments used as antioxidants in nutritional supplements and cosmetics. This article presents a comprehensive synopsis of the metabolic basis for accumulating lipids as well as applicable methods of lipid and cellulose bioconversion and final applications of these natural or refined products from microalgal biomass. For lipids, one-step in situ transesterification offers a new and more accurate approach to quantify oil content. As a complement to microalgal oil fractions, the utilization of cellulosic biomass from microalgae to produce bioethanol by fermentation, biogas by anaerobic digestion, and bio-oil by hydrothermal liquefaction are discussed. Collectively, a compendium of information spanning green renewable fuels and value-added nutritional compounds is provided.

Issues of cost and product quality have caused papermakers to place increased attention on the use of mineral additives, which are the subject of this review article. Technologists responsible for the production of paper can choose from a broad range of natural and synthetic mineral products, each of which has different characteristic shapes, size distributions, and surface chemical behavior. This article considers methods of characterization, and then discusses the distinguishing features of widely available filler products. The mechanisms by which fillers affect different paper properties is reviewed, as well as procedures for handling fillers in the paper mill and retaining them in the paper. Optical properties of paper and strategies to maintain paper strength at higher filler levels are considered. The goal of this review is to provide background both for engineers working to make their paper products more competitive and for researchers aiming to achieve effects beyond the current state of the art.