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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

We present a procedure, ASTM D7998-19, for a rapid and more consistent evaluation of both dry and wet strength of adhesive bonds on wood. The method can also be used to provide information on strength development as a function of temperature and time or strength retention up to 250 °C.

Abstract

The properties of cured wood adhesives are difficult to study because of the loss of water and other components to the wood, the influence of wood on the adhesive cure, and the effect of adhesive penetration on the wood interphase; thus, normal testing of a neat adhesive film is generally not useful. Most tests of wood adhesive bond strength are slow, laborious, can be strongly influenced by the wood and do not provide information on the kinetics of cure. Test method ASTM D 7998-19, however, can be used for fast evaluation of the strength of wood bonds. The use of a smooth, uniform, and strong wood surface, like maple face-veneer, and sufficient bonding pressure reduces the adhesion and wood strength effects on bond strength. This method has three main applications. The first is to provide consistent data on bond strength development. The second is to measure the dry and wet strengths of bonded lap shear samples. The third is to better understand the adhesive heat resistance by quickly evaluating thermal sensitivity and distinguishing between thermal softening and thermal degradation.

Introduction

Wood bonding is the largest single adhesive market and has led to efficient use of forest resources. For many centuries, solid wood was used for most applications, except for furniture construction, with no test criteria except product in-use durability. However, bonded wood products became more common, starting with plywood and glulam beams, using bio-based adhesives1,2. Although these products were satisfactory at the time, the replacement of soy, casein, and blood glues by synthetic adhesives containing formaldehyde led to improved properties. The higher performance of these new adhesives led to defined tes....

Protocol

1. Preparation of substrates

  1. Use a substrate surface that is suitable for the application. For wood, use a sliced veneer of about 0.6 to 0.8 mm thick from a reliable producer because these veneers are used for plywood and laminated veneer lumber (LVL) manufacturing. These are obtained from a veneer supplier, as sheets of 0.6 to 0.8 mm thickness and cut into 305 mm on a side. A consistent substrate is a hard maple (Acer saccharum) face veneer because of its surface smoothness and consistent thickness,.......

Representative Results

The procedure has been used extensively for the study of protein adhesives at the Forest Products Laboratory. It has been found that less than 2 MPa wet bond strength was insufficient to warrant further wood adhesive testing, while greater than 3 MPa was a promising result for further testing19. It has been shown to be useful in demonstrating sensitivity of wood processing conditions12,13. Further examples can be found in Frihart publicati.......

Discussion

Critical steps in the procedure are as follows: selection of substrates, preparation of specimens, operability of the equipment, and bonding of samples.

The substrate must be strong, have minimal defects (smooth, flat, no cracks and no discoloration. Unsanded, rotary cut cabinetry face veneer of a diffuse porous hardwood with sugar maple (Acer saccharum) preferred. Sanding creates a less even and more fragmented surface7. After conditioning the veneer at 21 .......

Acknowledgements

This work was supported by the United Soybean Board grant 1940-352-0701-C and the U.S. Department of Agriculture\Forest Service. We appreciate the support and detailed information from Phil Humphrey of AES.

....

Materials

NameCompanyCatalog NumberComments
AdhesiveSupplied by user
BalanceNormal supply house
Mark II Automated Bonding Evaluation System (ABES-II)Adhesive Evaluation Systems Inc
Pneumatically driven sample cutting deviceAdhesive Evaluation Systems Inc
Regular spatulaNormal supply house
Wood supply – Hard mapleBesse Forest Products Group

References

  1. Lambuth, A., Pizzi, A., Mittal, K. L. Protein adhesives for wood. Handbook of Adhesive Technology. , 457-477 (2003).
  2. Keimel, F. A., Pizzi, A., Mittal, K. L. Historical development of adhesives and adhesive bonding. Handbook of Adhesive Techn....

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ASTM D 7998 19Wood AdhesivesAbes Automatic Bond Evaluation SystemShear Bond StrengthAdhesive CuringSubstrate PreparationWood VeneerSpecimen PreparationAutomated Bonding Evaluation SystemAdhesive ApplicationSpecimen Bonding

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