Name: standard test method astm d 7998-19 for the cohesive strength development of wood adhesives
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Description: Watch this Scientific Journal Video about Standard Test Method ASTM D 7998-19 for the Cohesive Strength Development of Wood Adhesives at JoVE.com

This work was supported by the&#160;United Soybean Board grant&#160;1940-352-0701-C and the U.S.&#160;Department of Agriculture\Forest&#160;Service. We appreciate the support and detailed information&#160;from Phil Humphrey of AES.

1. Preparation of substrates
<ol>
	<li>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, and it is a diffuse porous and high modulus hardwood. Maple face veneers are commonly used in cabinetry construction and are usually free from defects.</li>
	<li>Condition the wood, unstacked, at 21 &#176;C and 50% relative humidity (RH) for at least a day prior to use. Avoid veneers that are excessively wavy, have an uneven surface, and contain defects including discoloration. 
	NOTE: Other wood species can be used to understand the bond performance of the adhesive with these species. However, diffuse-porous hardwoods and softwoods with a gradual earlywood-to-latewood transition are recommended for their uniformity. Take care because wood can be acidic or basic or have extractives on the surface that can alter the adhesive curing process. In addition, the processing of the tree from time of cutting to the veneer production can alter the bond strength12,13. Because the ABES uses a small amount of wood, it is less affected by wood variations that occur with other tests, such as wood moisture content and veneer check depth.</li>
	<li>Ensure that the sides of the veneer are free of any loose fibers along the edge and the bonded product does not have any significant adhesive squeeze out as these will tend to overestimate the bond strength since there is no post bonding modification of the samples.</li>
</ol>
2. Preparation of specimens
<ol>
	<li>Condition the wood specimens at 21 &#176;C and 50% RH for at least a day. Check the veneer for any cracks, discoloration, or grain irregularities to be avoided when cutting the specimens.</li>
	<li>Make sure that the pneumatically driven specimen cutting device is operational.</li>
	<li>Use a special die cutter that cuts the required specimen size of 20 mm by 117 mm from 0.6 to 0.8 mm thick maple veneer (Figure 1, Table of Materials).
	<ol>
		<li>Place a piece of veneer, at least 150 mm by 300 mm, under the cutting blades so that the veneer grain is parallel with the long direction and depress the air pressure button to cut each piece of wood of 20 mm by 117 mm.</li>
		<li>Move the piece of veneer under the cutting blades to an uncut area and depress the button again to cut another piece of wood. Continue until the piece of veneer is completely cut into pieces. 
		NOTE: If the long direction of the specimen is not parallel with the grain direction, during a test early fracture can occur in the wood away from the bonded portion.</li>
	</ol>
	</li>
	<li>For materials other than wood, cut the specimens using the appropriate techniques. If the material cannot be cut with the specimen cutter, use whatever will cut the material to cut it to the required size. Due to the small bonding area, it is important that cutting be accurate and the specimens free of debris along the edges and on the bonding surfaces.</li>
</ol>
3. Operability of the equipment
<ol>
	<li>For the bonding process, make sure that the ABES equipment is operating properly according to a standard operating procedure11. The settings on the front of the ABES unit for bonding and breaking samples are: LP Press 0.2 MPa, HP Press 0.2 MPa, Pull 0.65 MPa, and Cool Air 0.2 MPa.</li>
	<li>Use air supply pressure of at least 0.62 MPa (90 psig) because pressure that is too low will cause the gripping clamps and platens to close too slowly or unevenly on the sample resulting in incorrect bond strengths (Figure 2, top).</li>
	<li>Clean the platens of any adhesive resulting from squeeze out from the prior sample. Adjust the temperature of the platens to the desired temperature and equilibrate before bonding samples.</li>
	<li>To bond wood, operate the equipment in a room that is at 21 &#176;C and 50% RH. If this is not possible, keep the conditioned specimens in a plastic bag until bonding because of the rapid change in wood moisture due to the small size of the specimens.</li>
	<li>For obtaining kinetic cure data, design the method such that the mechanical and electronic speeds are sufficient to collect data accurately as outlined in ASTM D7998-1911.</li>
</ol>
4. Bonding of specimens with the adhesive
NOTE: The application of the adhesive is a critical issue for wood adhesives because of the wide variation in viscosity and percent solids going from a lamination adhesive as in plywood to a spray able adhesive for binder applications. Wood adhesives are generally water-borne so evaporation is only a minor problem. However, water soaking into the porous wood is important.
<ol>
	<li>Spread 5 mg of the adhesive being studied over the terminal 0.5 cm sufficiently to cover the bonding area and transfer to the other specimen but without excessive squeeze out. To obtain a relatively constant adhesive spread rate, tare the wood specimen on a balance and re-weigh after adhesive application.</li>
	<li>Exercise great care in distributing the adhesive, overlapping the specimens and making sure the two specimens are aligned, since a small bonding area is used and strengths are determined as the pull force over the bonded area (Figure 2 bottom). Different bonding areas can be used, but the strength is not necessarily comparable due to variation in the mechanics of lap shear tests. 
	NOTE: The literature recommends several ways to apply the adhesive to the wood depending on the adhesive consistency. The originally recommended adhesive application method used a purpose-designed microspraying device10, but this was found to be messy, slow, and very dependent on the adhesive rheology. Although this method applied the adhesive as discrete dots as used in binder applications for particleboard and oriented strandboard, a printing method seems more reliable14. The micro-pipette application method can supply a reproducible volume of adhesive10, but it is somewhat difficult to distribute evenly. The spatula method has worked the best for obtaining an even distribution of the adhesive on the bonding area, and a microbalance for obtaining a measured amount is recommended11.</li>
	<li>Final strength data
	<ol>
		<li>Bond the specimens at 120 &#176;C for 2 min and condition them overnight at 21 &#176;C and 50% RH since the hot pressing during bonding dries out the wood. To bond the wood, lock a sample in place by closing the grips on the ABES tester, making sure that the sample is aligned with the tester. Then press the start button on the machine to have the 120 &#176;C platens press on the overlapped section for 2 min, before retracting the platens and loosening the grips so that the samples can be removed. 
		NOTE: The time and temperature for curing are dictated by the application and adhesive chemistry. The bonding temperature and time should be optimized so that the strength reaches the highest plateau by using different bonding temperatures and times to determine conditions for maximum strength. For wood bonds, testing dry shear strength is valuable, but wet testing is generally more critical to determine adhesive durability and requires a 4 hour room temperature soak of the sample in water.</li>
		<li>For testing, lock a sample in place by closing the grips on the ABES tester making sure that the sample is aligned with the tester. Then by pressing the start button, the instrument pulls on one end through a servodrive while the other end of the sample pulls on a load cell attached to the grips. This pulling continues until the bond breaks. The computer records the maximum force the sample can withstand, which is recorded as bond strength.
		<ol>
			<li>Use the same procedure for the dry and water-soaked samples. In measuring the breaking force, take care to ensure that the grips hold the wood tightly because if the adhesive is very strong, the wood might slip. If the sample breaks outside the bonded area, discard the value since this is measuring the wood strength, not the adhesive.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Kinetic strength development
	<ol>
		<li>Determine the rate of strength development of an adhesive to estimate the press time required for large scale products. Follow the same procedure as in step 4.3, except vary the temperature and time. Begin the testing of strength at 100 &#176;C platen temperature, using bonding times of 10, 30, 60, 90, 120, 150, 180, and 210 seconds. Subsequently, raise the temperature by 10 &#176;C, and repeat the bonding times until there is no longer any linear section of strength versus time at the low bonding times.</li>
		<li>After bonding, retract the platens and use the air cooling feature of the ABES to cool the sample to near room temperature and then measure the sample strength. By starting at a low pressing time and increasing first the time for subsequent samples, collect the strength versus time data until increasing time results in little or no increasing strength. Then doing the same sequence at higher temperatures will yield the resulting plot of strength versus time and the cure rate as the slope (Figure 3). 
		NOTE: The phenolic adhesive data in Figure 3a10 shows the effect of temperature on the strength development at different times. Figure 3b shows the regressed isothermal strength development rate versus temperature. To obtain the isothermal strength development, the sample was cooled before testing. A few adhesives, such as urea formaldehyde15, have an optimum bonding time and temperature before degradation starts to take place. This method can detect this problem and determine optimum conditions.</li>
	</ol>
	</li>
	<li>Heat resistance
	<ol>
		<li>If the product needs to meet a certain temperature resistance, clamp the bonded sample into the ABES unit. After the platens are heated to that temperature, for example 220 &#176;C, above which wood starts to degrade, close them onto the pre-bonded sample for 2 min and then open to measure the bond strength as in 4.3.2 to determine any thermal softening of the adhesive compared to the bonding temperature of 120&#176;C.</li>
		<li>Repeat this test except that the platens are closed on the sample for 30 min and then tested for strength to determine strength if the adhesive is thermally degraded. Release of the platens and testing strength will determine the heat resistance of the sample compared to the value before heating. This type of procedure was used to test wood adhesives16. Since the ABES uses rapid heating and can measure strength while hot without moving the sample to another machine, it can be used to differentiate between the two modes of failure (i.e., thermal softening or degradation). Thermal softening produces strength loss immediately upon heating, and is typically recoverable. Chemical degradation occurs gradually over time at high temperature and does not recover mechanical strength on cooling. 
		NOTE: Adhesive manufacturers need to differentiate whether strength loss is from thermal softening or chemical degradation, because these problems require different solutions. There are many methods which can measure softening transitions including other thermal analyses, but they do not distinguish between a change in mechanical properties and chemical structure.</li>
	</ol>
	</li>
</ol>
5. Image analysis of failed bonding surface
<ol>
	<li>Because the main objective is to determine the adhesive strength or rate of cohesive strength development, make sure that failure is within the adhesive and not with adhesion to the substrate (Figure 4) or substrate failure. If substrate failure occurs, then the adhesive has sufficient strength. Alternatively, cohesive failure in the bulk adhesive indicates adhesive weakness. However, deciding between adhesion and adhesive interphase failure can be difficult17. A variety of methods have been developed for wood analysis18.</li>
</ol>

<ol>
	<li>Lambuth, A., Pizzi, A., Mittal, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+adhesives+for+wood.">Protein adhesives for wood.</a> Handbook of Adhesive Technology. , 457-477 (2003).</li><li>Keimel, F. A., Pizzi, A., Mittal, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Historical+development+of+adhesives+and+adhesive+bonding.">Historical development of adhesives and adhesive bonding.</a> Handbook of Adhesive Technology. , 1-12 (2003).</li><li>Marra, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Technology of Wood Bonding: Principles in Practice. , 454 (1992).</li><li>Dunky, M., Pizzi, A., Mittal, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adhesives+in+the+Wood+Industry.">Adhesives in the Wood Industry.</a> Handbook of Adhesive Technology. , 511-574 (2017).</li><li>River, B. H., Vick, C. B., Gillespie, R. H., Minford, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wood+as+an+adherend.">Wood as an adherend.</a> Treatise on Adhesion and Adhesives. , (1991).</li><li>Liswell, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploration+of+Wood+DCB+Specimens+Using+Southern+Yellow+Pine+for+Monotonic+and+Cyclic+Loading.">Exploration of Wood DCB Specimens Using Southern Yellow Pine for Monotonic and Cyclic Loading.</a> Engineering Mechanics. , (2004).</li><li>Frihart, C. R., Rowell, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wood+Adhesion+and+Adhesives.">Wood Adhesion and Adhesives.</a> Handbook of Wood Chemistry and Wood Composites. , 255-313 (2013).</li><li>Humphrey, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+device+to+test+adhesive+bonds.">A device to test adhesive bonds.</a> U.S. Patent. , (2003).</li><li>Humphrey, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temperature+and+reactant+injection+effects+on+the+bonding+kinetics+of+thermosetting+adhesives.">Temperature and reactant injection effects on the bonding kinetics of thermosetting adhesives.</a> Wood adhesives. , (2005).</li><li>Humphrey, P. E., Frihart, C. R., Hunt, C., Moon, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outline+Standard+for+Adhesion+Dynamics+Evaluation+Employing+the+ABES+(Automated+Bonding+Evaluation+System)+Technique.">Outline Standard for Adhesion Dynamics Evaluation Employing the ABES (Automated Bonding Evaluation System) Technique.</a> International Conference on Wood Adhesives 2009. , 213-223 (2010).</li><li>ASTM International. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> D 7998-19 Standard Test Method for Measuring the Effect of Temperature on the Cohesive Strength Development of Adhesives using Lap Shear Bonds under Tensile Loading, in Vol. 15.06. , (2019).</li><li>Rohumaa, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+felling+season+and+log-soaking+temperature+on+the+wetting+and+phenol+formaldehyde+adhesive+bonding+characteristics+of+birch+veneer.">The influence of felling season and log-soaking temperature on the wetting and phenol formaldehyde adhesive bonding characteristics of birch veneer.</a> Holzforschung. 68 (8), 965-970 (2014).</li><li>Rohumaa, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Log+Soaking+and+the+Temperature+of+Peeling+on+the+Properties+of+Rotary-Cut+Birch+(Betula+pendula+Roth)+Veneer+Bonded+with+Phenol-Formaldehyde+Adhesive.">Effect of Log Soaking and the Temperature of Peeling on the Properties of Rotary-Cut Birch (Betula pendula Roth) Veneer Bonded with Phenol-Formaldehyde Adhesive.</a> Bioresources. 11 (3), 5829-5838 (2016).</li><li>Smith, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+some+process+variables+on+the+lap-shear+strength+of+aspen+strands+uniformly+coated+with+pmdi-resin.">The effect of some process variables on the lap-shear strength of aspen strands uniformly coated with pmdi-resin.</a> Wood and Fiber Science. 36 (2), 228-238 (2004).</li><li>Pizzi, A., Pizzi, A., Mittal, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Urea-formaldehyde+adhesives.">Urea-formaldehyde adhesives.</a> Handbook of Adhesive Technology. , 635-652 (2003).</li><li>O'Dell, J. L., Hunt, C. G., Frihart, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+temperature+performance+of+soy-based+adhesives.">High temperature performance of soy-based adhesives.</a> Journal of Adhesion Science and Technology. 27 (18-19), 2027-2042 (2013).</li><li>Frihart, C. R., Beecher, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+that+lead+to+failure+with+wood+adhesive+bonds.">Factors that lead to failure with wood adhesive bonds.</a> World Conference on Timber Engineering 2016. , (2016).</li><li>Hunt, C. G., Frihart, C. R., Dunky, M., Rohumaa, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+wood+bonds:+going+beyond+what+meets+the+eye.">Understanding wood bonds: going beyond what meets the eye.</a> Reviews of Adhesives and Adhesion. 6 (4), 369-440 (2018).</li><li>Frihart, C. R., Dally, B. N., Wescott, J. M., Birkeland, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bio-Based+Adhesives+and+Reliable+Rapid+Small+Scale+Bond+Strength+Testing.">Bio-Based Adhesives and Reliable Rapid Small Scale Bond Strength Testing.</a> International Symposium on Advanced Biomass Science and Technology for Bio-based Products. , (2009).</li></ol>

The authors have nothing to disclose.

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 &#1...

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 testing standards with higher performance expectations than achievable with most bio-based adhesives. The synthetic adhesives also made possible the bonding of particles including sawdust to form particleboards, fibers to form fiberboards with varying densities, chips to provide oriented strandboard and parallel strand lumber, veneers to yield plywood and laminated veneer lumber, as well as finger jointed lumber, glulam, cross laminated lumber, and wood I-joists3. Each of these products have their own testing criteria4. Thus, the development of a new adhesive can require a lot of formulation work and extensive testing to determine if there is any potential for developing sufficient strength. This time-consuming testing and the complexity of wood properties and wood bonding5 has limited the development of new adhesives. In addition, the mechanical properties of wood adhesives can be different when cured between wood surfaces as opposed to neat6. Curing in contact with wood allows water and low molecular weight components from the adhesive to escape, in addition to complex interphase and chemical interactions of the adhesive with the wood3,7.
The development of the Automated Bonding Evaluation System (ABES) has been very helpful for understanding the strength development of wood adhesives because it is rapid and easy to use8,9,10. The system is an integral unit that bonds lap-shear samples and then measures the force under tension needed to break the bond. Its utility has led to development of ASTM method D7998-19 that uses this system11. Although this system was originally designed to measure adhesive strength development as a function of temperature and time, it can also measure the heat resistance of cured adhesives, as well as routine bond strength evaluation. Although the ABES test is a very useful preliminary screening tool, like any test, it has its limitations and does not replace all specific product strength and durability testing.
While there are many means of gauging the curing characteristics of adhesives, ranging from gel-time rheometry to differential scanning calorimetry, dynamic mechanical analysis, and spectroscopy of many types, only the ABES method measures the development of mechanical strength. This requires an instrument that is tightly controlled for heating, cooling, and in-place tensile testing11.

<table><tbody><tr><td>Adhesive</td><td>Supplied by user</td><td></td><td></td></tr><tr><td>Balance</td><td>Normal supply house</td><td></td><td></td></tr><tr><td>Mark II Automated Bonding Evaluation System (ABES-II)</td><td>Adhesive Evaluation Systems Inc</td><td></td><td></td></tr><tr><td>Pneumatically driven sample cutting device</td><td>Adhesive Evaluation Systems Inc</td><td></td><td></td></tr><tr><td>Regular spatula</td><td>Normal supply house</td><td></td><td></td></tr><tr><td>Wood supply &amp;ndash; Hard maple</td><td>Besse Forest Products Group</td><td></td><td></td></tr></tbody></table>

standard test method astm d 7998-19 for the cohesive strength development of wood adhesives

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.

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...

Watch this Scientific Journal Video about Standard Test Method ASTM D 7998-19 for the Cohesive Strength Development of Wood Adhesives at JoVE.com

Standard Test Method ASTM D 7998-19 for the Cohesive Strength Development of Wood Adhesives

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 &#176;C.

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 ...

standard-test-method-astm-d-7998-19-for-cohesive-strength-development

Universidad de Cartagena UDEC

Research

JoVE Journal

Bioengineering

2.8K Views.  USDA, Forest Service. 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.

Video: Standard Test Method ASTM D 7998-19 for the Cohesive Strength Development of Wood Adhesives

Preparation and Testing of Plant Seed Meal-based Wood Adhesives

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.

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.

Recently, the interest in plant seed meal-based products as wood adhesives has steadily increased, as these plant raw materials are considered renewable ...

Environment

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs ...

Engineering

Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they can delay or even prevent debonding failure. However, a major concern faced by designers is the premature failure of the anchors due to stress concentration. Poor installation quality and preparation of the clearance holes can result in stress concentration that provokes this premature failure. This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provide a proper quality control of the preparation of the drill hole. The method involves three parts: the drilling and cleaning of the holes, the smoothing of the hole edges with a customized drill bit, and the installation of the anchor itself, including the impregnation of the anchor dowel and its insertion. Anchor fans (the free length of the spikes) are then bonded to the external FRP reinforcement. For the end anchorage, and in the case of reinforcements with multiple plies, it is recommended that the anchor fan be inserted between two plies to assist the stress-transfer mechanism. 
The proposed procedure is complemented with a design approach for spike anchors, based on an extensive database. It is proposed that the design follow a number of steps, namely: selection of the anchor diameter and subsequent tensile strength of the connector (that is to say, the anchor before fanning out the free end), evaluation of the reduction in the tensile strength due to bending, provision of enough embedment to prevent slippage failure, and consideration of the number and spacing of anchors for a given reinforcement. In this sense, it should be noted that further research is needed in order to obtain a general expression for the contribution of spike anchors to overall bond strength of FRP reinforcements.

This manuscript presents a method for controlling the quality of installation for spike anchors designed to delay delamination of externally bonded fiber reinforced polymers. The protocol includes the preparation of the drill hole and the insertion process. The most influential parameters on the efficiency of the anchors are discussed.

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they ...

The Effect of Construction and Demolition Waste Plastic Fractions on Wood-Polymer Composite Properties

Construction and demolition waste (CDW), including valuable materials such as plastics, have a remarkable influence on the waste sector. In order for plastic materials to be re-utilized, they must be identified and separated according to their polymer composition. In this study, the identification of these materials was performed using near-infrared spectroscopy (NIR), which identified material based on their physical-chemical properties. Advantages of the NIR method are a low environmental impact and rapid measurement (within a few seconds) in the spectral range of 1600-2400 nm without special sample preparation. Limitations include its inability to analyze dark materials. The identified polymers were utilized as a component for wood-polymer composite (WPC) that consists of a polymer matrix, low cost fillers, and additives. The components were first compounded with an agglomeration apparatus, followed by production by extrusion. In the agglomeration process, the aim was to compound all materials to produce uniformly distributed and granulated materials as pellets. During the agglomeration process, the polymer (matrix) was melted and fillers and other additives were then mixed into the melted polymer, being ready for the extrusion process. In the extrusion method, heat and shear forces were applied to a material within the barrel of a conical counter-rotating twin-screw type extruder, which reduces the risk of burning the materials and lower shear mixing. The heated and sheared mixture was then conveyed through a die to give the product the desired shape. The above-described protocol proved the potential for re-utilization of CDW materials. Functional properties must be verified according to the standardized tests, such as flexural, tensile, and impact strength tests for the material.

Secondary material streams have been shown to include potential raw materials for production. Presented here is a protocol in which CDW-plastic waste as a raw material is identified, followed by various processing steps (agglomeration, extrusion). As a result, a composite material was produced, and mechanical properties were analyzed.

Construction and demolition waste (CDW), including valuable materials such as plastics, have a remarkable influence on the waste sector. In order for ...

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to diversify the fiber choices in the United States body armor market, copolymer fibers based on the combination of 5-amino-2-(p-aminophenyl) benzimidazole (PBIA) and the more conventional PPTA were introduced. Little is known regarding the long-term stability of these fibers, but as condensation polymers, they are expected to have potential sensitivity to moisture and humidity. Therefore, characterizing the strength of the materials and understanding their vulnerability to environmental conditions is important for evaluating their use lifetime in safety applications. Ballistic resistance and other critical structural properties of these fibers are predicated on their strength. To accurately determine the strength of the individual fibers, it is necessary to disentangle them from the yarn without introducing any damage. Three aramid-based copolymer fibers were selected for the study. The fibers were washed with acetone followed by methanol to remove an organic coating that held the individual fibers in each yarn bundle together. This coating makes it difficult to separate single fibers from the yarn bundle for mechanical testing without damaging the fibers and affecting their strength. After washing, fourier transform infrared (FTIR) spectroscopy was performed on both washed and unwashed samples and the results were compared. This experiment has shown that there are no significant variations in the spectra of poly(p-phenylene-benzimidazole-terephthalamide-co-p-phenylene terephthalamide) (PBIA-co-PPTA1) and PBIA-co-PPTA3 after washing, and only a small variation in intensity for PBIA. This indicates that the acetone and methanol rinses are not adversely affecting the fibers and causing chemical degradation. Additionally, single fiber tensile testing was performed on the washed fibers to characterize their initial tensile strength and strain to failure, and compare those to other reported values. Iterative procedural development was necessary to find a successful method for performing tensile testing on these fibers.

The primary goal of the study is to develop a protocol to prepare consistent specimens for accurate mechanical testing of high strength copolymer aramid fibers, by removing a coating and disentangling the individual fiber strands without introducing significant chemical or physical degradation.

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to ...

Chemistry

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, where the yarns in each layer are oriented parallel to each other and held in place using binder resins and thin polymer films. The armor is constructed by stacking the unidirectional layers in different orientations. To date, only very preliminary work has been performed to characterize the ageing of the binder resins used in unidirectional laminates and the effects on their performance. For example, during the development of the conditioning protocol used in the National Institute of Justice Standard-0101.06, UD laminates showed visual signs of delamination and reductions in V50, which is the velocity at which half of the projectiles are expected to perforate the armor, after ageing. A better understanding of the material property changes in UD laminates is necessary to comprehend the long-term performance of armors constructed from these materials. There are no current standards recommended for mechanically interrogating unidirectional (UD) laminate materials. This study explores methods and best practices for accurately testing the mechanical properties of these materials and proposes a new test methodology for these materials. Best practices for ageing these materials are also described.

The goal of the study was to develop protocols to prepare consistent specimens for accurate mechanical testing of high-strength aramid or ultra-high-molar-mass polyethylene-based flexible unidirectional composite laminate materials and to describe protocols for performing artificial ageing on these materials.

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, ...

Fabrication and Design of Wood-Based High-Performance Composites

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber ...

Evaluation of the Curing of Adhesive Systems by Rheological and Thermal Testing

The analysis of thermal processes associated to the curing of adhesives and the study of mechanical behavior once cured, provide key information to choose the best option for any specific application. The proposed methodology for the curing characterization, based on thermal analysis and rheology, is described through the comparison of three commercial adhesives. The experimental techniques used here are Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Rheology. TGA provides information about the thermal stability and filler content, DSC allows the evaluation of some thermal events associated to the cure reaction and to thermal changes of the cured material when subjected to temperature changes. Rheology complements the information of the thermal transformations from a mechanical point of view. Thus, the curing reaction can be tracked through the elastic modulus (mainly the storage modulus), the phase angle and the gap. In addition, it is also shown that although DSC is of no use to study the curing of moisture curable adhesives, it is a very convenient method to evaluate the low temperature glass transition of amorphous systems.

An experimental methodology based on thermal and rheological measurements is proposed to characterize the curing process of adhesives with to obtain useful information for industrial adhesive selection.

The analysis of thermal processes associated to the curing of adhesives and the study of mechanical behavior once cured, provide key information to choose ...

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as source of mechanical reinforcement in fully bio-based fiberboards was developed. Various lignocellulosic crop by-products have already been successfully pre-treated through this process, e.g., cereal straws (especially rice), coriander straw, shives from oleaginous flax straw, and bark of both amaranth and sunflower stems.
The extrusion process results in a marked increase in the average fiber aspect ratio, leading to improved mechanical properties of fiberboards. The twin-screw extruder can also be fitted with a filtration module at the end of the barrel. The continuous extraction of various chemicals (e.g., free sugars, hemicelluloses, volatiles from essential oil fractions, etc.) from the lignocellulosic substrate, and the fiber refining can, therefore, be performed simultaneously.
The extruder can also be used for its mixing ability: a natural binder (e.g., Organosolv lignins, protein-based oilcakes, starch, etc.) can be added to the refined fibers at the end of the screw profile. The obtained premix is ready to be molded through hot pressing, with the natural binder contributing to fiberboard cohesion. Such a combined process in a single extruder pass improves the production time, production cost, and may lead to reduction in plant production size. Because all the operations are performed in a single step, fiber morphology is better preserved, thanks to a reduced residence time of the material inside the extruder, resulting in enhanced material performances. Such one-step extrusion operation may be at the origin of a valuable industrial process intensification.
Compared to commercial wood-based materials, these fully bio-based fiberboards do not emit any formaldehyde, and they could find various applications, e.g., intermediate containers, furniture, domestic flooring, shelving, general construction, etc.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pretreatment on lignocellulosic biomass was developed, which leads to an increased average fiber aspect ratio. A natural binder can also be added continuously after fiber refining, leading to bio-based fiberboards with improved mechanical properties after hot pressing of the obtained extruded material.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as ...

Determination of the Mechanical Properties of Flexible Connectors for Use in Insulated Concrete Wall Panels

This document contains recommendations for performing a non-standard, double-shear test suitable for both continuous and discrete insulated concrete sandwich wall panels (ICSWPs). Such a standardized test does not exist, but several iterations of this and similar tests have been performed in the literature to varying degrees of success. Further, the tests in the literature are rarely-if ever-described in detail or discussed at length with respect to the testing, data analysis, or safety procedures. A test specimen configuration is recommended herein, and variations are discussed. Important mechanical properties are identified from the load versus displacement data, and their extraction is detailed. The use of test data for design, such as for determining the stiffness of the connectors, is briefly demonstrated to show how ICSWP deflection and cracking behavior may be calculated. The strength behavior of panels may be determined using the full load versus displacement curve or only the maximum connector strength. Shortcomings and unknowns are acknowledged, and significant future work is delineated.

We propose a testing protocol that can be combined with widely available analytical methods to assess the mechanical properties of shear connectors for use in the design of insulated concrete wall panels to predict full-scale insulated panel behavior.

This document contains recommendations for performing a non-standard, double-shear test suitable for both continuous and discrete insulated concrete ...