Introduction: (Initial Observation)
Wood glue is widely used at homes and businesses for construction or repair of wooden products. Wood glue is also used in connecting processed wood products such as papers and cardboards.
Many different materials have traditionally been used as wood glue. Some of such materials were extracted from animal and plant products. Modern wood glues are synthetic resins similar to plastics.
Not all wood glues are made of high quality resins. Some manufacturers use less glue in their products and add more water and more thickening material in order to reduce the cost.
In this project you will perform experiments to compare three or more different commercially available wood glues for their strength.
Information Gathering:
Gather information about wood glues. Read books, magazines or ask professionals who might know in order to learn about active ingredients of wood glues and how they work. Keep track of where you got your information from.
Following are samples of information that you may find.
Since 1500-1000 B.C. glue have been a method of assembly. Material used as glues at that time included sticky resins from tree sap, Egg white, fish and animal glues.
Other natural ingredients used to prepare glue were blood, bones, hide (skin of animals), milk, cheese, vegetables, and grains. Tar and beeswax have been used to caulk the planking in boats and ships.
The first commercial glue factory was started in Holland to manufacture animal glue from hides. About 1750, the first glue patent was issued in Britain for a fish glue. Patents were then rapidly issued for adhesives using natural rubber, animal bones, fish, starch, and milk protein (casein).
Animal Glues are made from the protein extracted from the bones, hide, hoofs, and horns of animals by boiling. The extract is cooked to form a gelatin material. The gelatin can the be re-liquified with heat, which gives it quick setting properties. Its major use has been in the wood and furniture industry. If you have seen a heated glue pot with a brush in it, it was probably an animal glue. Animal byproducts from meat processing have been the source of supply for this type of glue as well as the sources of jokes about old Dobbin being past his prime and only good for the “glue pot”.
Fish Glue is a similar protein-based glue made from the skins and bones of fish. An exceptionally clear adhesive can be made from fish and was the first adhesive used for photographic emulsions for photo film and photo resist coatings for photoengraving processes.
Casein Glue is made from a protein isolated from milk. The extraction process creates an adhesive that is waterproof. Its first use was in bonding the seam of cigarette paper. It provides a fast-setting bond that requires very little adhesive; one gram of adhesive can bond 2,000 cigarettes.
Starch is a carbohydrate extracted from vegetable plants such as corn, rice, wheat, potatoes, and is probably better known as paste. Major use area is in bonding paper and paper products such as bookbinding, corrugated boxes, paper bags, and wallpaper paste (nonremovable); it is also used as a sizing in textiles. The laundry uses starch on your shirt collars to stiffen and give shape to your shirt.
Cellulose Adhesive is made from a natural polymer found in trees and woody plants. It is the adhesive used on the cellophane wrapper on cigarette packs; it is the adhesive on decals we put on windows; and, interestingly enough, the adhesive used on the strippable wallpaper we have in our homes that allows us to remove the paper easily.
Rubber-Based Solvent Cements are adhesives made by combining one or more rubbers or elastomers in a solvent. These solutions are further modified with additives to improve the tack or stickiness, the degree of peel strength, flexibility, viscosity, or body. Rubber-based adhesives are used in a wide variety of applications, such as contact adhesive for plastic laminates like counter tops, cabinets, desks, and tables. It is the adhesive on pressure-sensitive tapes used as floor tile adhesive and carpeting adhesive. Self- sealing envelopes and shipping containers use rubber cements. Solvent-based rubber adhesives have been the mainstay of the shoe and leather industry.
Epoxies are adhesive systems made by a complex chemical reaction. Various resins are made synthetically by reacting two or more chemicals. The resultant resin can then be reacted or cured by the addition of another chemical called a hardener, or catalyst. The basic epoxy resin systems are further modified to change their physical properties by the addition of such things as: flexibilizers for impact resistance and flexibility; dilutents or solvents to reduce the viscosity fillers; and reinforcements like glass fiber, alumina, silica sand, clay, metal powders and flakes to change properties such as heat and electrical resistance, fire retardance, strength and adhesion to certain substrates or materials.
Epoxy adhesives can bond a wide variety of substrates (particularly metals) with high strength. They have been used to replace some traditional metalworking methods of joining like nuts and bolts, rivets, welding, crimping, brazing, and soldering. High- strength epoxies are used to construct rotor blades for helicopters and to attach aluminum skins to the struts of aircraft wings and tail sections. Those of you who ski may know that your skis are laminates of plastics, wood, and metal joined with an epoxy. If you are a golfer, the heads of your clubs are bonded with an epoxy.
Hot Melt Adhesives are thermoplastic polymers that are tough and solid at room temperature but are very liquid at elevated temperatures. The origin of hot melts probably started with the use of sealing wax used to seal documents and letters with a signature ring or stamp, but the art of hot melts was not pursued until the 1960s.
The major use of hot melt adhesive is in case and carton sealing. Probably if you purchased products such as frozen food, breakfast cereal, laundry detergent, a case of beer, or anything shipped in a corrugated box, the flaps were bonded with a hot melt adhesive. Hot melts are also used in home workshops for fast repairs around the home.
Other adhesives that you may have heard of that represent higher technology and/or complicated chemical processes include:
RTV Silicone Adhesives are a rubber-like polymer called polydimethysiloxanes. RTV stands for itroom temperature vulcanizing,ll or simply a rubber that cures at room temperature. Silicone rubber adhesives are made from a complicated process that turns elemental silicon metal made from sand (silica) into a rubbery polymer when cured. Silicone rubber adhesives/sealants have excellent resistance to heat (500-600F) and moisture, which makes them exceptionally suited for outdoor weathering applications as sealants and caulking compounds in the construction industry.
Because of their exceptional properties, silicone adhesives have been used in some exotic applications, such as the soles of boots worn by the first astronauts to walk on the moon. Silicone adhesive/sealants are used to seal windows, doors, and portholes on the space shuttle and many satellite missiles. A special silicone adhesive is used to bond the heat shield tiles on the space shuttle.
Anaerobic Adhesives are derived from methacrylates, a monomer related to acrylics or more commonly known as plexiglass. The term anaerobic is used to describe this family of adhesives because this type of adhesive idcomes to lifele or hardens in the absence of air. There are many different types of anaerobics used for specific applications such as threadlocking, threadsealing, flangesealing, or retaining.
Cyanoacrylates are extremely rapid curing adhesives commonly called “superglue”. These adhesives were actually discovered by accident at Eastman Chemical Company. In trying to characterize certain polymers, they ended up gluing their microscope slides together. Cyanoacrylates are typically used in applications where there is a need for a rapid-curing, single- component adhesive that provides high adhesion, high tensile strength, and easy dispensing. The following list demonstrates a few common, everyday items that use adhesives in some form and that would most likely not be around today if not for the existence of adhesives.
Adhesive materials > Natural adhesives > Blood albumen glue
Glue of this type is made from serum albumen, a blood component obtainable from either fresh animal blood or dried soluble blood powder to which water has been added. Addition of alkali to albumen-water mixtures improves adhesive properties. A considerable quantity of glue products from blood is used in the plywood industry.
The American Society for Testing and Materials (ASTM) defines an adhesive as a substance capable of holding materials together by surface attachment. An adherend is a substrate held to another substrate by an adhesive. Adhesion is the state in which two surfaces are held together by interfacial forces, which may be valence forces, interlocking action, or both. Valence forces are forces of attraction produced by the interactions of atoms, ions, and molecules that exist within and at the surfaces of both adhesive and adherend.
Interlocking action, also called mechanical bonding, means surfaces are held together by an adhesive that has penetrated the porous surface while it is liquid, then anchored itself during solidification. The extent to which valence forces and interlocking action develop between adhesive polymers and wood adherends is uncertain, but both are generally acknowledged as essential for the most effective bonding. Bonding to porous surfaces, such as wood, paper, and textiles, was thought to be primarily mechanical, but now there is evidence supporting bonding by primary valence forces. In contrast, bonding to hard metal surfaces was believed to involve only valence forces, but this is no longer the accepted view. Metal surfaces roughened by chemical etching or made microscopically porous with a layer of oxide are capable of mechanical interlocking with an adhesive to pro-duce exceptionally strong and durable bonds.
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to compare a few different wood glues for their strength .
Identify Variables:
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variable (also known as manipulated variable) is the wood glue (type or brand)
Dependent variable (also known as responding variable) is the strength of the wood glue.
Controlled variables are temperature, light, moisture.
Constants are the type of wood, the amount of glue, the drying time and the test method.
Experiment Design:
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1:
Introduction:
To test which wood glue is the strongest you can glue wood dowels along each other and then test to see what force can brake them apart from the glue point. Wood dowels are wooden sticks with a round cross section. You may also use other wooden sticks with the same results.
Procedure:
- Use 6 wood dowels (or wooden sticks) for each of the wood glues that you want to test. Label or mark wood dowels to represent the glue for that group.
- Divide each group to 3 pairs. For each pair apply one drop of glue on one end of one wood dowel and then connect it to one end of the second wood dowel. Keep them vertical so they can dry in that position.
- Let all glued wood dowels to dry in this position for a fixed number of hours (at least 5 hours). Now in each group you should have 3 long wood dowels.
- Place each long wood dowel between two stands or supports and then enter pressure to the center (joint). Observe and record the force that can break the wood dowels apart. Record the highest force before breakage point as the strength for each pair. Calculate the average strength for each group.
Record your experiment results in a table like this:
| Glue Type/brand | Strength 1 | Strength 2 | Strength 3 | Strength Average |
| Titebond | ||||
| Pro Wood | ||||
| Elmer’s |
Notes: As a source of force, you may use a strong spring scale or simply hang weights to see what weight leads to breakage.
The picture in the right shows a strength test setup.
In this setup two hooks are mounted on a wooden board about 10 inches apart. A set of MiniScience spring scales were used to test the strength. Test started with a 2.5 Newton (250 grams) scale that can enter forces from 0 up to 250 grams. The glued stick did not brake with this force. The next spring scales tried were 5 Newton (500 grams), 10N (1000 grams), 20N (2000 grams), and 30N.
While doing this test, we gradually increase the force by pulling the spring scale until the wood brakes. If one spring scale did not have enough force to brake the stick, switch to the next stronger spring scale.
Draw a graph:
Use the above results table to draw a graph that can visually show the results of your experiments. For this project you must use a bar graph. Your graph will have one vertical bar for each of the glue types or brands that you test. The height of the bar represents the average strength of that glue in your tests.
Write the name of each glue under or over each bar. Write the average strength above each bar.
Material and Equipment:
- Wood dowels (or wood sticks) available in your local craft stores or hardware stores.
- Different wood glues (available at hardware stores and craft stores)
- spring scale (available at MiniScience.com, klk.com and other science suppliers)
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Following are some pictures from the wood dowel preparations of these experiment.
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Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Conclusion:
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Possible Errors:
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
References:
Your references are this website and the books that you will find in your local library about glue. You can also include the websites of manufacturers and some of the following:
- History of Hide Glue. (Hides are the skin of animals)
- History of fish glue
- Adhesives
- Protein based glues
- Wood Adhesives
