Preparation and Testing of Plant Seed Meal-based Wood Adhesives

Summary

To facilitate the effort in seeking more economic and environment-friendly formulations of natural product-based wood adhesives, this work demonstrates the preparation and testing of plant seed-based wood adhesives. This protocol allows one to assess plant seed-based agricultural products as suitable candidates for the substitution of synthetic-based wood adhesives.

Abstract

Recently, the interest in plant seed meal-based products as wood adhesives has steadily increased, as these plant raw materials are considered renewable and environment-friendly. These natural products may serve as alternatives to petroleum-based adhesives to ease environmental and sustainability concerns. This work demonstrates the preparation and testing of the plant seed-based wood adhesives using cottonseed and soy meal as raw materials. In addition to untreated meals, water washed meals and protein isolates are prepared and tested. Adhesive slurries are prepared by mixing a freeze-dried meal product with deionized water (3:25 w/w) for 2 hr. Each adhesive preparation is applied to one end of 2 wood veneer strips using a brush. The tacky adhesive coated areas of the wood veneer strips are lapped and glued by hot-pressing. Adhesive strength is reported as the shear strength of the bonded wood specimen at break. Water resistance of the adhesives is measured by the change in shear strength of the bonded wood specimens at break after water soaking. This protocol allows one to assess plant seed-based agricultural products as suitable candidates for substitution of synthetic-based wood adhesives. Adjustments to the adhesive formulation with or without additives and bonding conditions could optimize their adhesive properties for various practical applications.

Introduction

Adhesive bonding of wood plays an increasing role in the forest product industry and is a key factor for efficiently utilizing timber resources¹. Interest in the use of natural product-based adhesives for wood increased steadily from the 1930s to reach a peak around 1960². After this period, the price of petroleum-based adhesives became so low that they displaced protein adhesives from several traditional markets. In the past two decades, this trend has reversed with renewed interest in the use of materials that are renewable, biodegradable, and more environmentally acceptable. These natural resources include, but are not limited to, soy protein<....

Protocol

1. Cottonseed and Soy Meal-based Products (Figure 1)

1. Obtain the raw materials, defatted cottonseed and soy meals, from commercially available sources.
2. Obtain the working meal by grinding the solid defatted meal in a cyclone sample mill to pass a 0.5 mm steel screen¹⁶.
3. Prepare water washed meals from the working meals after water extraction (25 g meal:200 ml water) to separate water soluble components in the meals²¹.
4. Prepare protein isolates from the working meals by alkali extraction and acid precipitation¹⁶.

2. Preparation of Wood Veneer Strips

1. Cu....

Results

Each adhesive formulation’s performance is determined by the shear strength of the bonded wood specimen at break and the values vary depending on the dimensions of the wood veneer used. For example, in Table 1, the dry and soaked adhesive strength values of the bonded specimens are lower when thinner and narrower maple strips are used (see Cottonseed-1), as opposed to the thicker and wider strips of Cottonseed-2 recommended in the protocol, using the same cottonseed-based adhesive formulation. Also obser.......

Discussion

This paper presents a basic procedure to prepare and test plant seed-based products as wood adhesives. The adhesive slurries exampled in this protocol are simply the defatted seed meal product and water. Various adhesive formulations can be reached by addition of testing reagents (such as sodium dodecyl sulfate, sodium bisulfite or tung oil)^5,6,23 and/or changes in mixing conditions (such as pH, ratio of solid and water)^3,24,25. Adjustment of the adhesive formulation is also needed if the rheologica.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Defatted cottonseed meal	Kentwood Co-op		Kentwood, LA, USA
Defatted soy meal	Kentwood Co-op		Kentwood, LA, USA
Wood veneers	Certainly Wood, Inc.		East Aurora, NY, USA
Cyclone sample mill (model 3010-014)	UDY Corporation		Fort Collins, CO, USA
Benchtop heated press (model 3856)	Carver, Inc.		Wabash, IN, USA
Materials tester	Zwick GmbH & Co.		Ulm, Germany