Lignocellulosic Fibers and Wood Handbook

Renewable Materials for Today's Environment

Mohamed Naceur Belgacem, A. Pizzi, Mohamed Naceur Belgacem, A. Pizzi

• Publisher: Wiley-Scrivener
• Year: 2016
• Print ISBN: 9781118773529
• eBook ISBN: 9781118773550
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

This book will focus on lignocellulosic fibres as a raw material for several applications. It will start with wood chemistry and morphology. Then, some fibre isolation processes will be given, before moving to composites, panel and paper manufacturing, characterization and aging.

Part 1

WOOD AND FIBRES: RAW MATERIALS

Chapter 1

Introduction and State-of-the-Art

Mohamed Naceur Belgacem and Antonio Pizzi

Industry is using several types of fibers in various applications such as composites, nonwoven materials, textiles, paper, etc. These strong materials can be classified as synthetic, artificial or natural fibers. Other classification criteria are available such as metallic, inorganic or organic fibers, optical, etc. Several subdivisions may also be given, as, for example, vegetal or animal fibers concerning the natural fibers family, or regenerated or modified regenerated types associated with artificial fibers.

Synthetic fibers are produced from synthetic polymers (the starting monomers are originating from fossil resources). The most common manufacturing processes of synthetic fibers are the Melt-Spinning and/or Solution-Spinning techniques. In both cases, the polymer is molten or dissolved in a solvent and drawn through well-calibrated nozzles, as quickly as possible. Such a process yields anisotropic fibers and allows the alignment of the polymer macromolecules in a parallel arrangement, providing them an easy crystallization, which in turn gives strong mechanical strength. In the Melt-Spinning process, the drying of the fibers is ensured by heat-loss, whereas in the Solution-Spinning technique this operation is guaranteed by solvent loss. The commercial synthetic fibers dominating the market are nylon, polyester, acrylic and polyolefin. Synthetic fibers are more durable than most natural fibers. They have several other advantages, such as stretching ability and water and stain resistance.

Lignocellulosic fibers are a worldwide natural material available from different sources. Moreover, this organic material possesses several advantages such as abundance, renewable character, low price, availability in different chemical composition and morphologies, low density, biodegradability at the end of life and many others. This remarkable raw material has always contributed to fulfilling the needs of industrial societies and has also played a key role in the development of a sustainable global economy. In fact, wood and its derivatives, as well as cellulose (used in the preparation of panels, textile and paper-based products), have played an important role as materials for humanity through their exploitation in a progressively more elaborated fashion. They have progressively shifted from empirical exploitation to more sophisticated technologies associated with papermaking, textile and wood processing.

Economic and environmental issues associated with the use of depleting fossil resources have placed the focus on lignocellulosic materials as a potential alternative feedstock for the production of chemicals, fuels and biocompatible materials. Thus, nowadays, in addition to the classical use of such materials (paper, wood and wood-based products and textiles), large contributions are emerging everywhere in the world that deal with the use of such a raw material for the production of bioethanol, biodiesel and as a reinforcing component in polymer composites. In fact, in the last context, wood-plastic and natural fibers-reinforced polymeric composites are a well-established industrial reality, even if more work is needed to achieve economically efficient industrialization in several sectors.

Lignocellulosic materials in general, and as fibers in particular, possess three major drawbacks: (i) they are highly polar and consequently very sensitive to water uptake and release; (ii) their chemical composition could vary as a function of the vegetal species, the growing conditions and soils, the season, the plant age, etc. This makes their industrial exploitation very hard to rationalize and renders them difficult to characterize. Thus, several innovative methods of lignocellulosic materials characterization are needed. In this context, recently, several advanced analytical techniques were developed, namely: time-of-flight secondary ion mass spectrometry, 2D heteronuclear single quantum correlation Nuclear Magnetic Resonance Spectroscopy, Atomic Force Microscopy, Field Emission Gun Scanning Electron Microscopy, Matrix Assisted Laser Desorption Ionization Mass Spectrometry and Raman microscopy.

Wood is a natural fibrous structural composite used by man for thousands of years as a construction material and to produce thermal energy. Wood is an organic material composed of cellulose fibers (reinforcing phase) embedded in lignin (a polyphenolic crosslinked polymer) as a matrix. Its third component is the hemicelluloses, which play the role of compatibilizing agent between the reinforcing cellulose fibers and the lignin matrix.

The amount of wood on earth is about one trillion tons, with a growing rate of about 3% per year. Wood has been always an important raw material for human needs. Thus, this remarkable natural material was used forever in construction of houses, doors, windows and boats. Wood has also served as water pipes. The use of engineered wood products is increasing in the construction industry, both for residential and commercial buildings, as structural and aesthetic materials. Cement- and concrete-based buildings also use wood as a supporting material, namely, as shuttering material (mold into which concrete is poured), interior doors and their frames, and as exterior cladding, wood flooring and others.

Wood can also be found in several other areas of applications, namely:

i. Sport articles: bats for cricket and baseball, NBA courts, skis, hockey sticks, lacrosse sticks. Some of these articles are now prepared using composite materials;

ii. Furniture (chairs and beds) and currently used disposable articles (chopsticks, toothpicks) and kitchen utensils, like spoons, but also outdoor furniture for public parks;

iii. Musical instruments of the violin and guitar families, clarinet, oboe, recorder, xylophone, and marimba;

iv. Art: sculptures, frames, etc.;

v. Communication and transport of goods and energy: telephone and electrical poles, wooden railway crossties, wooden pallets;

vi. Packaging for heavy articles and machinery, industrial goods, but also in the food industry such as cheese packaging and wooden crates for fragile fruits and vegetables. Finally, barrels for wine and luxury alcohols, such as Cognac, are also wood-based materials.

The wood industrial sector practically uses such a raw material in its integrality. Thus, wood waste, residue from construction wood unsuitable for construction, is mechanically milled to produce fibers or chips or chemically treated to prepare cellulose. The ensuing materials are used as a raw material for a variety of boards and panels. Thus, particleboard, oriented strandboard (OSB), hardboard and medium density fiberboard are all prepared by this route. An example is Medium-Density Fiberboard (MDF). MDF has several advantages, such as high stiffness and smoothness and the absence of knots, and it is isotropic and easily machined. During cutting and sanding, but also during the rest of its service life, although at a much lower rate, MDF can release hazardous substances, such as formaldehyde. Moreover, during these operations, very fine dust can be produced. Masks and goggles are recommended for people handling such operations.

Paper is a largely consumed commodity product throughout the world. In fact, the worldwide consumption of paper is around 400 millions of tons. The worldwide growing rate in this sector is around 3%. Several paper grades are available. They can be classified into three main categories: (i) printing and writing; (ii) packaging, and (iii) specialty paper grade. The first two families cover more than 90% of the overall paper marketed. They are commodity products. The last family is of high added value products. It includes security papers such as those used for money, passports, fiduciary documents, but also more common product such as carbonless, thermal (used for fax and invoices), fireproof papers, etc.

Paper has also been used for a long time by humanity. In the beginning it was mostly used as a communication medium, before shifting to a much larger number of applications. Most of them are classical, meaning conventional sectors like printing and writing paper, as well as packaging materials, tissues, photos, tubes and cores…. Others are very surprising, such as separator in batteries or in electrical capacitor, shuttering material, i.e., molds into which concrete is poured. Paper is also used to fulfill a very specific functionality in flexible films packaging, such as oil-proof, water-proof and release. The present tend...

Table of contents

• Cover
• Half Title page
• Title page
• Copyright page
• Dedication
• Preface
• Part 1: Wood and Fibres: Raw Materials
• Part 2: Wood and Fibres: Composites and Panels
• Part 3: Wood and Fibres: Paper
• Part 4: Wood and Fibres: Properties
• Index