Fundamentals of Composite Processing
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United States Department of Agriculture Fundamentals of Forest Service Forest Composite Products Laboratory General Processing Technical Report FPL−GTR−149 Proceedings of a Workshop Presented by the U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, Wisconsin in cooperation with the Wood-Based Composites Center, Virginia Tech, Blacksburg, Virginia Abstract Contents The USDA Forest Service, Forest Products Laboratory Page (Madison, Wisconsin) and the Wood-Based Composites Center of Virginia Tech (Blacksburg, Virginia) co-sponsored Preface ................................................................................iii a conference, held November 5–6, 2003, in Madison, Wis- Overview of Composites Processing ..................................iv consin, on the fundamentals of composite processing. The goals were to assess what we know, define what we need to General Processing Considerations .................................iv know, and then establish the state of the art in hot-pressing of wood-based, particulate composites. Academic and indus- Oriented Strandboard ......................................................iv trial professionals from around North America and Europe were invited to participate because of their expertise and Fiberboard ........................................................................ v interest in this area of research. The workshop covered four critical topics associated with hot-pressing of composites: Fundamentals of Composite Processing..........................vi resin curing and bonding, press control, physics of hot- Workshop Introduction........................................................ 1 pressing, and computer simulations of the pressing process. This report is the official record of the presentations and Physics of Hot-Pressing ....................................................... 3 discussions that occurred during this workshop. Discussion ...................................................................... 19 Keywords: composites, processing, engineered wood Monitoring Resin Cure in the Mat for Hot-Compression Modeling............................................... 26 Adhesive Interactions With Wood..................................... 29 Discussion ...................................................................... 39 Press Control for Optimized Wood Composite Processing and Properties—Part 1: Pressing Variables and Sensors........................................................ 54 Press Control for Optimized Wood Composite June 2004 Processing and Properties—Part 2: Properties and Press Control Strategies .............................................. 65 Winandy, Jerrold E.; Kamke, Frederick A., Eds. 2004. Fundamentals of composite processing. Proceedings of a workshop; November 5–6, 2003; Discussion ...................................................................... 83 Madison, WI. Gen. Tech. Rep. FPL-GTR-149. Madison, WI: U.S. Depart- ment of Agriculture, Forest Service, Forest Products Laboratory. 118 p. Simulation of the Pressing Process .................................... 90 A limited number of free copies of this publication are available to the public from the Forest Products Laboratory, One Gifford Pinchot Drive, Discussion .................................................................... 102 Madison, WI 53726–2398. This publication is also available online at www.fpl.fs.fed.us. Laboratory publications are sent to hundreds Summary and Wrap-up .................................................... 113 of libraries in the United States and elsewhere. The Forest Products Laboratory is maintained in cooperation with the Appendix—Participant List ............................................. 116 University of Wisconsin. The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. Department of Agriculture of any product or service. The United States Department of Agriculture (USDA) prohibits discrimina- tion in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact the USDA’s TARGET Center at (202) 720–2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW, Wash- ington, DC 20250–9410, or call (202) 720–5964 (voice and TDD). USDA is an equal opportunity provider and employer. Fundamentals of Composite Processing Proceedings of a Workshop Presented by the U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, Wisconsin in cooperation with the Wood-Based Composites Center Virginia Tech, Blacksburg, Virginia November 5–6, 2003 Madison, Wisconsin Jerrold E. Winandy, Workshop Co-Chair and Editor U.S. Department of Agriculture Forest Service Forest Products Laboratory One Gifford Pinchot Drive Madison, Wisconsin 53726–2398 Frederick A. Kamke, Workshop Co-Chair Wood Science and Forest Products 1650 Ramble Road Blacksburg, VA 24061 3 4 Preface The goals and objectives of this November 2003 workshop were related to those of an earlier workshop on composite consolidation held at Virginia Tech, Blacksburg, Virginia, in September 1990. The consensus from that first workshop was that process engineering required knowledge of the levels and rates of heat and mass (that is, mois- ture) transfer within a consolidating mat, considering that it could consist of a diverse array of materials. That knowledge was then used to explain why and how much those thermodynamic factors influenced both the chemistries and physical states of wood ma- terials and resins within a consolidating composite mat. The use of models to interpolate between known conditions was endorsed. But, participants also reached consensus that models should not be black boxes spouting conditions. Rather, they should facilitate our understanding of what is going on and when events occur within a mat. The goal of this second workshop is to assess what have we learned since 1990, identify what it is that we still need to know, and then re-establish the state of the art in hot- pressing of wood-based, particulate composites. Academic and industrial professionals from around North America and Europe were invited to participate because of their expertise and interest in this area of research. This workshop was hosted by the U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, in cooperation with the Wood-Based Composites Center at Virginia Tech in Blacksburg, Virginia. It was chaired by Jerrold E. Winandy (FPL), with formal presentations offered by Chunping Dai (Forintek–Canada Ltd) Charles Frazier (WBC Center, Virginia Tech) Charles Frihart (FPL) Frederick A. Kamke (WBC Center, Virginia Tech) Heiko Thoemen (University of Hamburg) Siqun Wang (University of Tennessee) More than 30 participants also attended the workshop at their own expense. Those par- ticipants are listed in the Appendix. The organizers of this workshop would like to thank the presenters and all the workshop attendees for their valuable contributions to this re- appraisal of the state of the art and the fundamentals of composite processing. Jerrold E. Winandy Workshop Chairman Madison, Wisconsin iii Overview of Composites In the general manufacturing process for OSB, debarked logs are often heated in soaking ponds and then sliced into Processing thin wood elements. The strands are dried, blended with Before we begin this review of the presentations and discus- resin and wax, and formed into thick, loosely consolidated sion that occurred during our workshop, a brief, general mats that are pressed under heat and pressure into large overview may be appropriate to help some readers under- panels. Figure 1 shows an overview of the OSB manufactur- stand the current state of the art in composites processing. ing process. Oriented strandboard is made from long, narrow strands, with the strands of each layer aligned parallel to one Today, many wood-based composite materials are normal another but perpendicular to strands in adjacent layers, like materials in our day-to-day lives. These composites are the cross-laminated veneers of plywood. It is this perpen- usually available in panel form and are widely used in hous- dicular orientation of different layers of aligned strands that ing and furniture. Wood composites are typically made with gives OSB its unique characteristics and allows it to be a heat-curing adhesive that holds the wood fibers or wood- engineered to suit different uses. particle components together. Each type of wood-based fiber or wood-particle panel composites uses different wood Typically, logs are debarked and then sent to a soaking pond materials and resins and has different physical and mechani- or directly to the stranding process. Long log disk or ring cal properties and surface characteristics. Thus, their manu- stranders are commonly used to produce wood strands typi- facturing processes and intended uses vary accordingly. cally measuring 114 to 152 mm (4.5 to 6 in.) long, 12.7 mm (0.5 in.) wide, and 0.6 to 0.7 mm (0.023 to 0.027 in.) thick. General Processing Considerations Green strands are stored in wet bins and then dried in a Still, most products