Tech Talk Blog

Diallyl Phthalate (DAP)
The term DAP is used both for the monomeric and polymeric forms. The monomer [C₆H₄(COOCH₂CHCH₂)₂] is used as a cross-linking agent in unsaturated polyester resins. As a polymer, it is used in the production of thermosetting molding powders, casting resins and laminates. This material can be bonded using most epoxies. Paint adhesion can be improved using plasma pretreatment.

Epoxy
Thermosetting resins that, in the uncured form, contain one or more reactive epoxide or oxirane groups. These epoxide groups serve as cross-linking points in the subsequent curing step, in which the uncured epoxy is reacted with a curing agent or hardener. Cross-linking is accomplished through the epoxide groups as well as through hydroxyl groups that may be present. Most conventional unmodified epoxy resins are produced from epichlorohydrin (chloropropylene oxide) [CH₂OCHCH₂Cl] and bisphenol A [(CH₃)₂C(C₆H₄OH)₂]. The other types of epoxy resins are phenoxy resins, novolac resins, and cycloaliphatic resins. Epoxy resins are used as protective coatings, bonding adhesives, in building and construction, and for electrical , and many other uses….This material can be modfied for improved strength and or temperature resistance.

Fluoropolymer
A family of thermoplastic resins analogous to polyethylene in which some of the hydrogen atoms attached to the carbon chain are replaced by fluorine or fluorinated alkyl groups. In some cases, other halogens such as chlorine are also part of the molecule. The most common commercial fluoropolymers are: FEP (fluorinated ethylene-propylene) from tetrafluoroethylene [C₂F₄] and hexa-fluoropropylene [C₃F₆]; PTFE (polytetra fluoroethylene) from the polymerization of tetrafluoroethylene and ethylene [C₂H₄]; PFA (perfluoroalkoxy) from tetrafluoroethylene and perfluoropropyl vinyl ether [C₃H₇C₄OF₅]; PCTFE (polychlorotrifluoro-ethylene) from chlorotrifluoro-ethylene monomer [C₂F₃CI]; CTFE-VDF (polychlorotrifluoroethylenevinylidene fluoride) from chlorotrifluoroethylene and vinylidene fluoride [C₂H₂F₂]; E-CTFE (polyethylenechlorotrifluoroethylene) from chlorotrifluoroethylene and ethylene; PVDF (polyvinylidene fluoride) from vinylidene fluoride monomer; and PVF (polyvinyl fluoride) from vinyl fluoride monomer [C₂H₃F]. Typical applications for fluoropolymers are found in electrical/ electronic uses and pipe and chemical processing equipment. Requires chemical etch or plasma treatment for adhesion.

Melamine-Formaldehyde
Thermosetting resins formed by the condensation reaction of formaldehyde [HCHO] and melamine [C₃N₃(NH₂)₃]. The chemistry is analogous to that of ureaformaldehyde except that the three amino groups of melamine provide more possibilities for cross-linking, are more highly reactive, and all six hydrogen atoms of melamine will react, forming the hexamethyl compound. Typical applications are found in bonding and adhesives, coatings, and consumer products.

Nitrile Resins
Thermoplastic resins composed of acrylonitrile [CH₂CHCN] along with comonomer such as acrylates, methacrylates, butadiene [CH₂CHCHCH₂] and styrene [C₆H₅CHCH₂]. Both straight copolymers and copolymers grafted onto elastomeric backbones are available. The unique property of these materials is outstanding resistance to passage of gases and water vapor, making them useful in packaging applications.

Nylon
A generic name for a family of long-chain polyamide engineering thermoplastics which have recurring amide groups [-CO-NH-] as an integral part of the main polymer chain. Nylons are synthesized from intermediates such as dicarboxylic acids, diamines, amino acids and lactams, and are identified by numbers denoting the number of carbon atoms in the polymer chain derived from specific constituents, those from the diamine being given first. The second number, if used, denotes the number of carbon atoms derived from a diacid. Commercial nylons are as follows: nylon 4 (polypyrrolidone)-a polymer of 2-pyrrolidone [CH₂CH₂CH₂C(O)NH]; nylon 6 (polycaprolactam)-made by the polycondensation of caprolactam [CH₂(CH₂)₄NHCO]; nylon 6/6-made by condensing hexamethylenediamine [H₂N(CH₂)₆NH₂] with adipic acid [COOH(CH₂)₄COOH]; nylon 6/10-made by condensing hexamethylenediamine with sebacic acid[COOH(CH₂)₈COOH]; nylon 6/12-made from hexamethylenediamine and a 12-carbon dibasic acid; nylon 11-produced by polycondensation of the monomer 11-amino-undecanoic acid [NH₂CH₂(CH₂)₉COOH]; nylon 12-made by the polymerization of laurolactam [CH₂(CH₂]₁₀CO)or cyclododecalactam, with 11 methylene units between the linking -NH-CO- groups in the polymer chain. Typical applications for nylons are found in automotive parts, electrical/electronic uses, and packaging. This material can be easily bonded after plasma treatment or with methylene chloride/ethylene dichloride.

Petroleum Resins
Thermoplastic resins obtained from a variable mixture unsaturated monomers recovered as byproduct from cracked and distilled petroleum streams. They also contain indene [C₆H₄CH₂CHCH], which is copolymerized with a variety of other monomers including styrene [C₆H₅CHCH₂], vinyl toluene [CH₂CHC₆H₄CH₃], and methyl indene [C₆H₃CH₃CH₂CHCH]. Typical applications are found in adhesives, printing inks, rubber compounding, and surface coatings.

Phenolic
These thermosetting resins are credited with being the first commercialized wholly synthetic polymer or plastic. The basic raw materials are formaldehyde [HCHO] and phenol [C₆H₅OH], although almost any reactive phenol or aldehyde can be used. The phenols used commercially are phenol, cresols [CH₃C₆H₄OH], xylenols [(CH₃)₂C₆H₃OH], p-t-butylphenol [C₄H₉C₆H₄OH], p-phenylphenol [C₆H₅C₆H₄OH], bisphenols [(C₆H₄OH)₂], and resorcinol [C₆H₄(OH)₂]. The aldehydes used are formaldehyde and furfural [C₄H₃OCHO]. In the uncured and semi- cured condition, phenolic resins are used as adhesives, casting resins, potting compounds, and laminating resins. As molding powders, phenolic resins can found in electrical uses. Easily bonded using epoxies. Enhanced paint and coating adhesion can be accomplished using plasma treatments.

Polyamide-Imide
Engineering thermoplastic resins produced by the condensation reaction of trimellitic anhydride [OCC₆H₂C₂O₃] and various aromatic diamines. Typical applications are found in aerospace, automotive and heavy equipment industries. Plasma treatment is very effective at improving coating and adhesive adhesion.

Polyarylates
Engineering thermoplastic resins produced by interfacial polymerization of an aqueous solution of the disodium salt of bisphenol A [(CH₃)₂C(C₆H₄OH)₂] with phthalic acid chlorides [C₆H₄(CO)₂Cl₂] in methylene chloride (CH₂Cl₂]. The major use of polyarylates is in outdoor lighting.

Polybutylene
Thermoplastic resins produced via stereospecific Ziegler-Natta polymerization of butene-1 monomer [CH₂CHCH₂CH₃]. Typical applications are found in pipe and packaging film.

Polycarbonate
Engineering thermoplastic resins produced by (1) phosgenation of dihydric phenols, usually bisphenol A [(CH₃)₂C(C₆H₄OH)₂], (2) ester exchange between diaryl carbonates and dihydric phenols, usually between diphenyl carbonate [(C₆H₅O)₂CO] and bisphenol A and (3) interfacial polycondensation of bisphenol A and phosgene [COCl₂]. Typical applications are found in glazing, appliances, and electrical uses. Can be bonded using solvents like ethylene dichloride. But, a more “green” approach is by using plasma treatments.

If you have any questions about the list, Ask The Experts. And if you’re a visual learner, look to our Video Learning Center for more information.

Part 3 is on its way…

Acetal
An engineering thermoplastic produced by the polymerization of purified formaldehyde [CH₂O] into both homopolymer and copolymer types. Typical applications are found in consumer products, automotive parts, and industrial machinery parts. Bonding or painting this material requires plasma treatment.

Acrylics
A family of thermoplastic resins of acrylic esters [CH₂CHCOOR] or methacrylic esters [CH₂C(CH₃)COOR]. The acrylates may be methyl, ethyl, butyl, or 2-ethylhexyl. Usual methacrylates are the methyl, ethyl, butyl, laural and stearyl. Typical applications are found in lighting fixtures, glazing and automotive parts. Bonding or painting this material can be accomplished with solvents or plasma treatments. Solvent bonding may be prohibited in some areas, in this case plasma treatment is necessary.

Acrylonitrile-Butadiene-Styrene (ABS)
A class of thermoplastic terpolymers including a range of resins, all prepared with usually more than 50% styrene [C₆H₅CHCH₂] and varying amounts of acrylonitrile [CH₂CHCN] and butadiene [CH₂CHCHCH₂]. The three components are combined by a variety of methods involving polymerization, graft copolymerization, physical mixtures and combinations thereof. Typical applications are found in appliances, automotive parts, pipe, business machine and telephone components. Bonding or painting this material can be accomplished with solvent or plasma treatments.

Alkyds (Thermosets)
Thermosetting unsaturated polyester resins produced by reacting an organic alcohol with an organic acid, dissolved in and reacted with unsaturated monomers such as styrene [C₆H₅CHCH₂], diallyl phthalate [C₆H₄(COOCH₂CHCH₂)₂], diacetone acrylamide [CH₃COCH₂C(CH₃)₂CHCHCONH₂] or vinyl toluene [CH₂CHC₆H₄CH₂]. Typical applications are found in electrical uses, automotive parts, and as coatings. Most can be bonded with epoxies or nitrile-phenolic adhesives. Painting this material usually requires plasma treatment.

Cellulosics
A family of thermoplastic resins manufactured by chemical modification of cellulose [(C₆H₁₀O₅)n]. Included are: cellophane—regenerated cellulose made by mixing cellulose xanthate [ROCSSH] with a dilute sodium hydroxide [NaOH] solution to form a viscose, then extruding the viscose into an acid bath for regeneration; cellulose acetate—an acetic acid ester [CH₃COOC₂H₅] of cellulose; cellulose acetate butyrate—a mixed ester produced by treating fibrous cellulose with butyric acid [CH₃CH₂CH₂COOH], butyric anhydride [(CH₃CH₂CH₂CO)₂O], acetic acid [CH₃COOH] and acetic anhydride [(CH₃CO)₂O] in the presence of sulfuric acid [H₂SO₄]; cellulose propionate— formed by treating fibrous cellulose with propionic acid [CH₃CH₂CO₂H] and acetic acid and anhydrides in the presence of sulfuric acid; cellulose nitrate—made by treating fibrous cellulosic materials with a mixture of nitric [HNO₃] and sulfuric acids. Typical applications are found in packaging, consumer products, and automotive parts. This material can be bonded or painted using solvents, but plasma treatment with most standard adhesives also works very well and is a more “green” approach.

Coumarone-Indene
Thermoplastic resin obtained by heating mixtures of coumarone [C₈H₆O] and indene [C₆H₄CH₂CHCH] with sulfuric acid [H₂SO₄] to promote polymerization. These resins have no commercial applications when used alone. They are used primarily as processing aids, extenders and plasticizers with other resins in asphalt floor tile. There is no hope bonding this material.

Stand-by for part 2… If you have more questions, Ask The Experts – they know a thing or two. Or surf the TriStar site to learn more yourself!

However, because the substrates are deformed in tension, the shear stresses are concentrated at the ends of the overlap in a lag effect. When a joint is loaded the adhesive stresses beyond its elasticity point and on further loading the adhesive is stressed beyond its yield point in shear and regions of uniform stress develop at the edges of the joint. As the load is increased, these uniform shear regions will spread through the whole of the overlap and a limit will be reached when the joint can carry no further load. An upper limit on strength can therefore be derived as

Pmax = tyLb

Where:

1. Pmax     is the maximum joint strength possible
2. ty            is the adhesive yield stress in shear

This maximum strength is not achieved because the shear strains exceed the limits for the adhesive, the effect of peels stresses and failure of the substrate.

Lap shear bond stresses without load

Lap shear bond stresses without a load

Lap shear bond under load

Lap shear bond under load

Experimental data for the shear stress distribution indicate that:

Where:

1. tmax     is the maximum adhesive shear stress
2. Ga          is the shear modulus of the adhesive
3. Es           is the Young’s modulus of the substrate
4. ta            is the thickness of the adhesive layer
5. ts            is the thickness of the substrate

Thus, the bigger the ratio between the stiffness of the substrate and the adhesive layer, the more uniform the shear stress distribution.

The next post will illustrate examples of bonding joints with qualitative comments as to their performance.

As always, you can check out our Shooting Star Archives to read about real-world applications or visit the TriStar site.

The design of an adhesive bond may be simple or complicated depending on the adhesives function. For optimum performance of the materials and adhesive, some general principles should be considered:

1. Stress in the direction of maximum strength
2. Maximize bonding surface
3. Adhesive applied uniformly
4. Adhesive is thin and continuous
5. Minimize stressed areas

It is important to know the duration, direction and load of the forces being applied to designed joint. Most adhesives used for structural purposes are relatively strong in shear. Conversely, these same adhesives have relatively low adhesive strength in tensile or peel.

The design of the bond line should take into consideration the forces that occur when the device is under load. A simple lap shear bond has peel forces at the ends while the center observes little stress.

For lap joints loaded in tension, the load is transferred predominantly by shear stresses in the adhesive layer. If the adhesive was loaded uniformly then

ta = [ P / (Lb) ]

Where:

1. ta         is the adhesive shear stress
2. P          is the load
3. L          is the overlap length
4. b          is the width

The next post will expand on this discussion and provide more details about shear bonds under stress…

But if you can’t wait – look to our Video Learning Center for more information right now!

Acrylic or poly(methyl 2-methylpropenoate) is a specific group of thermoplastics. Methyl methacrylate is polymerized in bulk or suspension methods using free-radical initiators.

PMMA - polymer chain

The presence of the pendant methyl (CH₃) groups prevents the polymer chains from packing closely in a crystalline fashion and from rotating freely around the carbon-carbon bonds. As a result, PMMA is strong, transparent and somewhat inert.

Bonding untreated PMMA to itself is limited to either cyanoacrylate, dichloromethane (CH₂Cl₂), or trichloromethane (CHCl₃). The bond strength using these methods is strong and can exceed the strength of the acrylic substrates. Unfortunately, these adhesive may not be effective when bonding acrylic to other materials. When acrylic is to be bonded to materials other than itself, plasma treatment can assist in enhancing the bond strength.

A plasma is a quasineutral cloud of ion, electrons, and radicals. The diffuse cloud is capable of doing chemistry on the surface of materials that is unique, providing wettable or adherent surfaces on materials that are otherwise inert.

The PMMA samples in this study were subjected to a specific plasma gas mixture to induce and adherent surface for a structural epoxy adhesive. The results are as follows:

In summary, PMMA can be bonded using mechanical or solvent chemical methods. Yet, it has been proven that plasma surface modification is a viable, environmentally friendly, invisible treatment that can enhance the bonding performance significantly. For more informtion about this process please contact us at our Tristar Plasitics Corp. website.

Using simple plasma surface modification techniques, we are able to manipulate the surface of most plastic devices to contain fluids or direct flow.

Surface treatment zone

the surface treatment zone shown in the picture above is 0.9mm. The wet zones are hydrophilic drawing water into the narrow zone while the other areas are hydrophobic to the natural polystyrene material.

If you would like more information about this process, please vist our website.

There are two primary reasons that dye fades:

1.) The dye is loosely attached into a device and “falls out”. A good analogy to visualize this effect is water on a screen door. Visualize the dye as the water and the screen as the polymer.The dye will remain in place until the polymer is stressed; like snapping the wet screen.

2.) The dye molecules are ‘excited” by UV and combine on contact with the oxygen in the air. In other words they are pulled out of the material by a chemical reaction that occurs normally.

Dyes can also fade to some extent due to the heating of the polymer in hot weather conditions, perspiration and cleaning. Most customers are instructed to wash polymers in warm, soapy water. When the lenses are cleaned the top most layer of the dye molecules is wiped away. You can reduce the effect of the first, but can do nothing to prevent the second. Unless a clear top coat from TriStar Plastic’s product line is used. To discuss your particular needs, please visit our website Tristar Plastics.

The expansion due to applied heat under ideal circumstances will occur in three dimensions, but with thin film flexible substrates, a mismatch in the coefficient of thermal expansion will result in interfacial stress causing curl.

Case 1.  The coating has a higher coefficient of thermal expansion vs. the substrate:

Case 2.  The coating has a lower coefficient of thermal expansion vs. the substrate:

Case 3. Coatings of relatively higher modulus may respond to interfacial stress to the extent that any substrate thermal expansion will cause cracking, crazing, and loss of adhesion.  Such failure may not occur until the system has been repeatedly cycled through extremes of temperature.