Non-Wood Lignocellulosic Composites

It would seem that with appropriate treatment almost any agricultural residue may be used as a suitable raw material for the wood-based panels like particle- and fiberboard production. The literature on wood-ligno-cellulose plant composite boards highlights steady interest for the design of new structures and technologies towards products for special applications with higher physical-mechanical properties at relatively low prices. Experimental studies have revealed particular aspects related to the structural composition of ligno-cellulose materials, such as the ratio between the different composing elements, their compatibility, and the types and characteristics of the used resins. Various technologies have been developed for designing and processing composite materials by pressing, extrusion, airflow forming, dry, half-dry, and wet processes, including thermal, chemical, thermo-chemical, thermo-chemo-mechanical treatments, etc. Researchers have undertaken to determine the manufacturing parameters and the physical-mechanical properties of the composite boards and to compare them with the standard PB, MDF, HB, SB made from single-raw material (wood). A great emphasis is placed on the processability of the ligno-cellulose composite boards by classical methods, by modified manufacturing processes, on the types of tools and processing equipment, the automation of the manufacturing technologies, the specific labor conditions, etc. The combinations of wood and plant fibers are successful, since there is obvious compatibility between the macro- and microscopic structures, their chemical composition, and the relatively low manufacturing costs and high performances, as compared to synthetic fiber-based composite materials.

Surface and Subsurface Quality Evaluation of Engineered Wood Products by Ultrasonic Means

The use of ultrasonic techniques to evaluate the properties of engineered wood-based materials is discussed with respect to research to date and the use of more advanced techniques. The latter is critical because of the rapid evolution from solid wood to reconstituted structural materials. In addition, although considerable research has been done, there have been few introductions into manufacturing. This chapter traces the history of the use and latest developments of ultrasonics in several key areas, particularly the measurement of adhesive curing and quality in composites and laminates, and detection of flaws in solid wood materials. The techniques reviewed apply to product development, material properties, process control, product quality assessment, and evaluation of products in service.

Natural Adhesives, Binders, and Matrices for Wood and Fiber Composites

Recent developments and trends in the field of bio-based adhesives are reviewed. The more recent developments in tannin adhesives without the use of aldehyde-yielding compounds under the conditions of processing, or even without the use of hardeners, are described. Lignin adhesives are discussed next. The combination of these two types to yield natural environmentally friendly matrices for non-woven fiber mats is also reviewed. Several new trends in the developments of protein adhesives and in carbohydrate adhesives are then addressed. Unsaturated oil adhesives based on epoxidized unsaturated vegetable oils are also described as well as an example of cashew nut shell oil modified by a new and inexpensive method to yield an adhesive by self-condensation of the material. The chapter addresses last the new process of solid wood friction welding without the use of adhesive, in which the wood interface itself is used as the binder.

Wood and Fiber Panel Technology

The influence on the preparation of wood and fiber panels of adhesives and wood, with concepts such as surface wettability, wood plasticization, glass transition temperature, and models of cell walls buckling are presented and discussed. Parameters of manufacturing at the industrial level are presented, and the relationship between panel properties and a number of manufacturing parameters such as press temperature, type of pressing cycle, maximum pressure, and relative surface/core moisture content are discussed. The scanning electron microscopy showing the appearance of the adhesive/wood interface is briefly presented. The concept of density profile in relation to panel properties and how to influence it is discussed. Different manufacturing equipment is presented, in particular fundamental differences between single daylight, multi-daylight, and continuous panel presses and their effect on panel properties and performance.

Bonding Defect Imaging in Glulam with Novel Air-Coupled Ultrasound Testing

The objective of this chapter is to provide an overview of novel non-destructive testing methodologies for bonding quality assessment in glued laminated timber developed within a recently completed Swiss National Science Foundation research project (Sanabria, 2012). The focus is set on air-coupled ultrasound testing, which has previously been applied to wood-based panels typically up to 50 mm thick. A novel prototype capable of transmitting ultrasound signals through up to 500 mm thick glulam was developed. A computerized-scanning system allowed imaging of the position and geometry of defects within the bonding planes. A normal transmission setup allows a global assessment of defective bonding planes stacks. Latest results are as well shown for a recently patented slanted lateral transmission setup, which allows separate assessment of individual bonding planes with unlimited beam height and length. The investigations allowed an improved understanding of the wave propagation phenomena in thick laminated timber components through both analytical calculations and finite-difference numerical simulations. An overview of the main findings is as well provided. Future research is planned to combine the developed theoretical and experimental tools in a tomographic inspection method.

Modern Testing of Wood-Based Panels, Process Control, and Modeling

The fast development of the wood-based panels industry during the last decades resulted in a substantially increased production capacity of manufacturing lines. The utilization of advanced manufacturing systems created a large output of different panel types with a production of more than 1,000 m3 per day on at least 300 days within a year. Therefore, it is important to take into account the new requirements for an on-line control of the manufacturing process. Only on-line Non-Destructive Testing (NDT) technologies are able to survey, detect, and forecast the quality of the raw materials, level of production parameters, and development of the panel properties. Main parameters like moisture content, resination level, mat area weight, thickness, and density profile influence the final properties of the panels. For over a decade there has been no other choice to control these and other process parameters than NDT methods using microwave (water content), IR (moisture and color), X-ray (mat and board area weight and density profile), ultrasound (blisters or density variation), etc. The determination of the effective resin content on the wood particle or the density, temperature, and moisture development during the hot pressing are further requirements for the future production units. The on-line measurement of free formaldehyde remaining after resin curing and other volatile substances from wood and resin seems to be a further subject of major interest. The intelligent implementation and integration, use, and understanding of on-line NDT methods in wood panel manufacturing is a big challenge that includes a better understanding of the overall process and its limits, an updated state of the art of knowledge, as well as an open and continuous dialog between the equipment producers, board manufactures, and users that could be another important key for the development of an environmentally friendly modern wood-based panel industry in the world.

Wood-Based Composites

Wood composites are made from various wood or ligno-cellulosic non-wood materials (shape and origin) that are bonded together using either natural bonding or synthetic resin (e.g. thermoplastic or duroplastic polymers), or organic- (e.g. plastics)/inorganic-binder (e.g. cement). This product mix ranges from panel products (e.g., plywood, particleboard, strandboard, or fiberboard) to engineered timber substitutes (e.g., laminated veneer lumber or structural composite lumber). These composites are used for a number of structural and nonstructural applications in product lines ranging from interior to exterior applications (e.g. furniture and architectural trim in buildings). Wood composite materials can be engineered to meet a range of specific properties. When wood materials and processing variables are properly selected, the result can provide high performance and reliable service. Laminated composites consist of wood veneers bonded with a resin-binder and fabricated with either parallel- (e.g. Laminated Veneer Lumber with higher performance properties parallel to grain) or cross-banded veneers (e.g. plywood, homogenous and with higher dimensional stability). Particle-, strand-, or fiberboard composites are normally classified by density (high, medium, low) and element size. Each is made with a dry woody element, except for fiberboard, which can be made by either dry or wet processes. Hybrid composites based on wood wool, particles, and floor mixed with cement or gypsum are used in construction proving high weathering and fire resistance in construction. The mixture with plastics (PP or PE) and wood floor open a new generation of injected or molded Wood Plastic Composites (WPC), which are able to substitute plastics for some utilizations. In addition, sandwich panels with light core made from plastic foams or honeycomb papers are used in the furniture industry.

Inventory of Experimental Works on Cutting Tools’ Life for the Wood Industry

Woodworking is based on a trinomial machine/piece/tool. For maximum quality of the manufactured piece, it is important not to separate this trinomial, but the limited life of tools prevents that permanent contact. This phenomenon is due to the wear of the cutting parts of the tools. The prevention of wear is based on two methods. The first is to anticipate the end point of tool wear, changing these after a fixed period, no matter what. The other school is to recognize the tool wear at the event: the tools are changed once they are really worn out, finding faults on manufactured parts. A worn tool generates pieces with non-compliant quality or even unusable. A deeper understanding of wear and its consequences would change the tool at the right time. The tool wear for wood is due to several phenomena interacting with each other. The first dominating phenomenon is a corrosive attack that decreases the mechanical strength of the surface. The second is an abrasive attack whose work is facilitated by the reduced resistance of the surface. Repeated shocks can be in the degradation of the cutting edge, temperature acting as amplifier to wear. Understanding of the wear patterns can characterize the life of tools by wear measurement to find ways to extend this period with development of tool coatings, while maintaining optimal conditions for woodworking to get the best finish.

3D Non-Destructive Evaluation Techniques for Wood Analysis

Non-destructive testing techniques allow the analysis of wood characteristics without altering its end-use capabilities. Wood morphology, wood density, moisture content, and wood decay are some of the features detectable by means of different non-destructive methods. Among them, Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) stand out because of their ability to measure information in a three-dimensional fashion. This enables one to scan volumetrically an entire tree log, giving measurements of each location of the analyzed volume. The output data can provide information about internal structures or physiological features, which can then be used for optimizing industrial processing or for research purposes. In this chapter, the authors describe CT and MRI in terms of their operational principles, sampling conditions, data outputs, and advantages and disadvantages.