Craftsmanship

Diana wunderle — Fri, 03 Oct 2008 07:22:14 GMT

(Our motto, here, is... "KNOW YOUR STUFF!")

This section is devoted to issues, tips, tricks, and the business of craftsmanship. Ever wondered how they got that magnificent finish? How others manage to make thier craft pay? Or perhaps whether or not there is a cheaper alternative to using those very expensive retail products?

Whether you are a hobby crafter or a dedicated professional, you will find information and resources, here, of benefit. This is where we will attempt to answer such questions. Not only myself, but perhaps a guest or two. After all, I don't have ALL the answers. Fortunately, I have a wealth of experts to call upon who are willing to divulge some of the best kept secrets of Master Craftsmen. So, if you have a question please send me an email. I will do my best to provide you with the best, time tested and latest trends, in Craftsmanship.

Our topic this month is adhesives:

Generally speaking...

**The manufacturers are the best source of information about a product.

I keep these on hand:

*Elmer's variety of paper and wood glue

* sticky dots

* super glue (very limited application), epoxies, plastic weld, u-tac, spray adhesive.

* Spar varnish may double as adhesive for certain wood projects.

* Gorilla Glue looks like spar varnish, but works well with polymer clay. The amber color gives an aging effect.

* Clear casting resin is a good, self leveling, adhesive for plastics and acrylic.

**ALWAYS pay attention to health warnings and recommendations!!!

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There are a wide variety of adhesives out there, under so many brand names. What are they, really? You might be shocked by some of the features of the most common types of household and craft glues. But I will give you a run down on a few that you might not be so familiar with, also.

To begin with, you might want to recall some of the chemistry lessons from high school or college. Adhesives are binders. You will find them in everything from food and medicine to just about any man made item.

Historically speaking, mankind probably learned about binders from watching animals. (Beavers and mud daubers come to mind.) In any case, binders and binding agents are a very basic necessity of human existence, and have been with us for as long as we have been putting two sticks together.

Nature made binders include such things as a variety of muds, sands, lime, hot lava, calcium, tree saps, tars, animal fats and feces.

It's no surprise that the adhesives we work with today are all based upon the same principles and chemical interactions as the nature made materials. No matter how much we synthesize, manipulate, or alter... we are still working with the basic principles of our environment. We utilize nature and natural principles, because that is the extent of what is available to us. This is an important basic concept from which to proceed when discussing chemical processes, because we will be discussing toxicity and caustic aspects of these elementary principles, also.

Beginning with a common name...

Elmer's Glue is one of the most common brand names known to us in the USA. A variety of popular household and craft adhesives are marketed under this name, including wood glue, paper glue, and the paste your kids ate in kindergarten. You may not know that Elmer's hosts an entire family of products under various names, including Beinfang and KrazyGlue:

Elmer's.com XACTO.com KrazyGlue.com ForFramersOnly.com ColorLoco.com GiddyUp.com RossGlue.com ScientificExplorer.com GALT.com

Elmer's Glues are chemical based. They are made or formulated from chemicals which are synthesized (created by Man). These chemicals were originally obtained or manufactured from petroleum, natural gas and other raw materials found in Nature. The exact formula and specific ingredients used in making Elmer's products are considered proprietary information, therefore, we cannot share those with you.

Manufacturers are required by law to provide MSDS (Material Safety Data)information about all products. http://www.elmers.com/product/prod_list.asp?prodCat=1

Thier white glue is a PVAC BASED ADHESIVE, the pastes are METHYL CELLULOSE.

Polyvinyl acetate (PVA or PVAc) is a rubbery synthetic polymer. It is prepared by polymerization of vinyl acetate monomer, also referred to as VAM. Partial or complete hydrolysis of the polymer is used to prepare polyvinyl alcohol. Hydroylized alcohol product is typically in the 87% to 99% range (converted PVA). It was discovered in Germany by Dr. Fritz Klatte in 1912.

As an emulsion in water, PVA is sold as an adhesive for porous materials, particularly wood, paper, and cloth. It is the most commonly used wood glue, both as "white glue" and the yellow "carpenter's glue." PVA is widely used in bookbinding and book arts due to its flexibility, and because it is non-acidic, unlike many other polymers.

PVA is a common copolymer with more expensive acrylics, used extensively in paper, paint and industrial coatings, referred to as vinyl acrylics. It can also be used to protect cheese from fungi and humidity. It is slowly attacked by alkali, forming acetic acid as a hydrolysis product. Boron compounds like boric acid or borax will form tackifying precipitates by causing the polymer to cross-link.

PVA is also commonly recommended for use in making leather handcrafted works and papier-mâché.

"http://en.wikipedia.org/wiki/Polyvinyl_acetate"

Methylcellulose (or methyl cellulose) is a chemical compound derived from cellulose. It is a hydrophilic white powder in pure form and dissolves in cold (but not in hot) water, forming a clear viscous solution or gel. It is sold under a variety of trade names and is used as a thickener and emulsifier in various food and cosmetic products, and also as a treatment of constipation. Like cellulose, it is not digestible, not toxic, and not allergenic.

Chemistry

Chemically, methylcellulose is a methyl ether of cellulose, arising from substituting the hydrogen atoms of some of cellulose's hydroxyl groups -OH with methyl groups -CH₃, forming -OCH₃ groups.

Different kinds of methylcellulose can be prepared depending on the number of hydroxyl groups so substituted. Cellulose is a polymer consisting of numerous linked glucose molecules, each of which exposes three hydroxyl groups. The Degree of Substitution (DS) of a given form of methylcellulose is defined as the average number of substituted hydroxyl groups per glucose. The theoretical maximum is thus a DS of 3.0, however more typical values are 1.3 - 2.6.

Different methylcellulose preparations can also differ in the average length of their polymer backbones.

Methylcellulose does not occur naturally and is synthetically produced by heating cellulose with caustic solution (e.g. a solution of sodium hydroxide) and treating it with methyl chloride.

The CAS number of methylcellulose is 9004-67-5.

Retrieved from WIKI: http://en.wikipedia.org/wiki/Methylcellulose

Addressing adhesion failure, I will borrow from Wiki:

Failure of the adhesive joint

When subjected to loading, debonding may occur at different locations in the adhesive joint. The major fracture types are the following:

Cohesive fracture

“Cohesive” fracture" is obtained if a crack propagates in the bulk polymer which constitutes the adhesive. In this case the surfaces of both adherents after debonding will be covered by fractured adhesive. The crack may propagate in the centre of the layer or near an interface. For this last case, the “cohesive” fracture can be said to be “cohesive near the interface”. Most quality control standards consider that a “good” adhesive bonding must be “cohesive”.

Interfacial fracture

The fracture is “adhesive” or “interfacial” when debonding occurs between the adhesive and the adherent. In most cases, the occurrence of “interfacial” fracture for a given adhesive goes along with a smaller fracture toughness. The “interfacial” character of a fracture surface is usually to identify the precise location of the crack path in the interphase.

Failure of the adhesive joint can occur in different locations

Other types of fracture

Beside these two cases, other types of fracture are

The “mixed” fracture type which occurs if the crack propagates at some spots in a “cohesive” and in others in an “interfacial” manner. “Mixed” fracture surfaces can be characterised by a certain percentage of “adhesive” and “cohesive” areas.
The “alternating crack path” fracture type which occurs if the cracks jumps from one interface to the other. This type of fracture appears in the presence of tensile pre-stresses in the adhesive layer.
Fracture can also occur in the adherent if the adhesive is tougher than the adherent. In this case the adhesive remains intact and is still bonded to one substrate and the remnants of the other. For example, when one removes a price label, adhesive usually remains on the label and the surface. This is cohesive failure. If, however, a layer of paper remains stuck to the surface, the adhesive has not failed. Another example is when someone tries to pull apart Oreo cookies and all the filling remains on one side. The goal in this case is an adhesive failure, rather than a cohesive failure.

The Wondercraft Reporter

Craftsmanship

Cohesive fracture

Interfacial fracture

Other types of fracture