Tech Talk Blog

Blocking - The greater the level of treatment, the higher the degree of oxidation of the surface. The polar groups formed by the corona have an attraction for the molecular layer on the other side of the web, and when the two sides come into contact when they are on the roll, a self-adhering condition exists.  Sometimes this attraction can be greater than the internal bonds of the substrate so that delamination of the substrate can occur when the product is unrolled.  The tighter the roll is wound and the longer it is in storage the more severe the problem becomes.  Blocking is worse in the film at the center of the roll.

Heat Sealing – Excessive treatment also leads to problems when attempting to heat seal the product.

Additives – If the polypropylene or polyethylene contain additional components, such as slip additives or some processing aids, the initial treatment is reduced over time as these additives bloom to the surface and partially mask the polar groups formed during treatment. For this reason, it is better to treat these films at the point of use rather than the point of manufacture.

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This study examined the relative adhesion difference between untreated polycarbonate (PC), mechanically roughened PC, and plasma treated PC. It appears that plasma surface modification of PC based polymers is a viable way to enhance adhesion prior to bond-up, lamination, or overmolding. This study observed approximately a 459% increase in lap shear bond strength after plasma treatment.

 Polycarbonate is a specific group of thermoplastics. They are called polycarbonates because they are polymers having functional groups linked together by carbonate groups in a long molecular chain.

The most common type of polycarbonate plastic is one made from Bisphenol A, in which groups from Bisphenol A are linked together by carbonate groups in a polymer chain. This polymer is highly transparent to visible light and has better light transmission characteristics than many kinds of glass. Polycarbonate can be mechanically bonded by standard methods. It can also be cemented by using a solvent such as methylene chloride or adhesives such as epoxy, urethane and silicone. Polycarbonate and also be ultrasonically welded. Yet, solvent based adhesive can contaminate sensitive devices. Moreover, ultrasonic welding requires tight tolerances and smooth contaminate-free surfaces. The plasma treatment prior to bonding with common adhesive has shown an effective way to bond PC without solvent based adhesive or technically difficult, sonic welding. 

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 PC 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, polycarbonate 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. If you would like more information about this process or other processes, please contact us at www.tstar.com.

Recent improvements in the pretreatment of certain fillers used in PTFE compounds has dramatically improved wear life. Carbon fibers are traditionally used for improving strength, heat transfer and electrical properties of PTFE. However, new chemical enhancements of the carbon fiber has resulted in dramatic tribological advances. By treating the fibers with plasma first, it prepares the surface for other chemical attachments. Experiments with nitric acid, amino silanes and two rare earth solutions showed varying degrees of improvement in both friction and wear. The best combination was plasma followed by a rare earth sol comprised of lanthanum oxide. This showed a reduction of dynamic friction to 0.054 and a K factor of 3.4, both exceptional numbers for a PTFE compound. New chemical modifications of fillers are being introduced which will lead to even more interesting new opportunities for seals, bearings and other dynamic application of PTFE compounds.

Take a look at our Video Learning Center for more information and our TriStar site.

Polyvinyl Acetate (PVAc) & Other Vinyls
Polyvinyl acetate is a thermoplastic resin produced by the polymerization of vinyl acetate monomer [CH₃COOCHCH₂] in water producing an emulsion with a solids content of 50-55%. Most polyvinyl acetate emulsions contain co-monomers such as n-butyl acrylate, 2-ethyl hexyl acrylate, ethylene, dibutyl maleate and dibutyl fumarate. Polymerization of vinyl acetate with ethylene also can be used to produce solid vinyl acetate/ethylene copolymers with more than 50% vinyl acetate content. Polyvinyl alcohol (PVOH) is produced by methanolysis or hydrolysis of polyvinyl acetates. The reaction can be controlled to produce any degree of replacement of acetate groups. Co-polymers of replaced acetate groupings and other monomers such as ethylene and acrylate esters are commercially important. Polyvinyl butyral (PVB) is made by reacting PVOH with butyraldehyde [CH₃(CH₂)₂CHO]. Polyvinyl formal is made by condensing formaldehyde [HCHO] in presence of PVOH or by the simultaneous hydrolysis and acetylization of PVAc. Polyvinylidene chloride is made by the polymerization of 1,1-dichloroethylene [CH₂CCL₂]. Typical applications for the above resins are found in adhesives, paints, coatings and finishes, and packaging.

Polyvinyl Chloride
Thermoplastic resins produced by the polymerization of the gas vinyl chloride [CH₂CHCl]. Under pressure, vinyl chloride becomes liquefied and is polymerized by one of four basic processes: suspension, emulsion, bulk, or solution polymerization. The pure polymer is hard, brittle and difficult to process, but it becomes flexible when plasticizers are added. A special class of PVC resin of fine particle size, often called dispersion grade resin, can be dispersed in liquid plasticizers to form plastisols. The addition of a volatile diluent or a solvent to the plastisol produces an organosol. Copolymers with vinyl acetate, vinylidene chloride, and maleate and fumarate esters find commercial application. Major markets for PVC are in building/construction, packaging, consumer and institutional products, and electrical/electronic uses. This material bonds effectively using solvents. Plasma treatments can enhance the adhesion of this material if solvents are not used.

Styrene Acrylonitrile
Thermoplastic copolymers of styrene [C₆H₅CHCH₂] and acrylonitrile [CH₂CHCN]. SAN resins are random, amorphous copolymers produced by emulsion, suspension, or continuous mass polymerization. Typical uses include automobile instrument lenses and housewares. Typically, this material does not have adhesion issues.

Styrene Butadiene Latexes & Other Styrene Copolymers
Styrene butadiene latexes usually have a resin content of about 50%. The styrene/butadiene ratio varies from 54:46 to 80:20. Most are carboxylated by the use of such acids as maleic [HOOCCHCHCOO], fumaric [HOOCCHCHCOOH], acrylic [CH₂CHCOOH], or methacrylic [CH₂C(CH₃)COOH]. Two types of styrene-maleic anhydride (SMA) [(COCH)₂O] are available: SMA copolymers, with and without rubber impact modifier (e.g., DYLARK¨) and SMA terpolymer alloys (e.g., CADON¨). K-Resin¨ is a solid styrenebutadiene copolymer resin. Acrylic monomers are also used in conjunction with styrene (or styrene plus other monomers) to produce specialty resins. For example, there are transparent terpolymers of methyl methacrylate, butadiene, and styrene (MBS), and others of acrylonitrile, an acrylic monomer, and styrene (AAS). Ion-exchange resins or divinylbenzene-modified polystyrene are another variation. SB latexes are used in carpet backing and paper coatings. The other styrenics are used in paints, coatings, and floor polishes, plus many other uses. Typically this material can be bonded using solvents. Moreover, these materials are enhanced after plasma treatment using other adhesives.

Sulfone Polymers
A family of engineering thermoplastic resins characterized by the sulfone [SO₂] group. Polysulfone is made by the reaction of the disodium salt of bisphenol A[(CH₃)₂C(C₆H₄OH)₂] with 4,4′- dichlorodiphenyl sulfone 4,4′-DCDPS [(C₆H₄Cl)₂SO₂]. Polyethersulfone is made by the reaction of 4,4′-DCDPS with potassium hydroxide [KOH]. Polyphenylsulfone is similar to the other sulfone polymers. Typical applications for sulfone polymers are found in electrical/electronic uses and automotive parts. Plasma treatments often enhance the adhesion of this material significantly using epoxies.

Thermoplastic Polyester (Saturated)
A family of polyesters in which the polyester backbones are saturated and hence nonreactive. The most common commercial types are: PET (polyethylene terephthalate) produced by polycondensation of ethylene glycol [CH₂OHCH₂OH] with either dimethyl terephthalate (DMT) [C₆H₄(COOCH₃)₂] or terephthalic acid (TPA) [C₆H₄(COOH)₂]; and PBT (polybutylene terephthalate) produced by the reaction of DMT with 1,4 butanediol [HO(CH₂)₄OH]. Typical applications are found in packaging, automotive, electrical, and consumer markets. Plasma treatments enhance this material when using epoxy.

Unsaturated Polyester
Thermosetting resins made by the condensation reaction between difunctional acids and glycols. The resulting polymer is then dissolved in styrene [C₆H₅CHCH₂] or other vinyl unsaturated monomer. The structures of the acids and glycols used and their proportions, especially the ratio of the unsaturated versus the saturated acid, and the type and amount of monomer used, are all tailored for each resin to balance economy, processing characteristics, and performance properties. One common formulation is the reaction of maleic anhydride [(COCH)₂O], phthalic anhydride [C₆H₄(CO)₂O], and propylene glycol [CH₃CHOHCH₂OH]. Both dicyclopentadiene [C10H1₂] and isophthalic acid [C₆H₄(COOH)₂] can be substituted for phthalic anhydride. Vinyl ester resins are linear reaction products of bisphenol A [(CH₃)₂C(C₆H₄OH)₂] and epichlorohydrin [CH₂OCHCH₂Cl] that are terminated with an unsaturated acid such as methacrylic acid [CH₂C(CH₃)COOH]. Typical applications are found in transportation, appliances, electrical, and construction markets. As in the above material, plasma treatments enhance this material when using epoxy.

Urea-Formaldehyde
Formed by the condensation reaction of formaldehyde [HCHO] and urea [CO(NH₂)₂]. These thermoset resins are clear water-white syrups or white powered materials which can be dispersed in water to form colorless syrups. They cure at elevated temperatures with appropriate catalysts. Molding powders are made by adding fillers to the uncured syrups, forming a consistency suitable for compression and transfer molding. The liquid and dried resins find extensive uses in laminates and chemically resistant coatings. The molding compounds are formed into rigid electrical and decorative products.

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Hope those were enough definitions for you!

Polyethylene
A family of thermoplastic resins obtained by polymerizing the gas ethylene [C₂H₄]. Low molecular weight polymers of ethylene are fluids used as lubricants; medium weight polymers are waxes miscible with paraffin; and the high molecular weight polymers (i.e., over 6000) are the materials used in the plastics industry. Polymers with densities ranging from about .910 to .925 are called low density; those of densities from .926 to .940 are called medium density; and those from .941 to .965 and over are called high density. The low density types are polymerized at very high pressures and temperatures, and the high density types at relatively low temperatures and pressures. A relatively new type called linear low density polyethylene is manufactured through a variety of processes: gas phase, solution, slurry, or high pressure conversion. A high efficiency catalyst system aids in the polymerization of ethylene and allows for lower temperatures and pressures than those required in making conventional low density polyethylene. Copolymers of ethylene with vinyl acetate, ethyl acrylate, and acrylic acid are commercially important. Major polyethylene applications can be found in packaging, housewares, toys and communications equipment. Can be bonded effectively after plasma treatments or by using our UltraFlon Bond-X 1606.

Polyimides
A family of thermoset and thermoplastic resins characterized by repeating imide linkages: There are four types of aromatic polyimides: (1) condensation products made by the reaction pyromellitic dianhydride (PMDA) [C₆H₂(C₂O₃)₂] and aromatic diamines such as 4,4′-diaminodiphenyl ether [(C₆H₄NH₂)₂O]; (2) condensation products of 3,4,3′,4′-benzophenone tetracarboxylic dianhydride (BTDA) [(C₆H₅)₂CO(C₂O₃)₂] and aromatic amines;(3) the reaction of BTDA and a diisocyanate such as 4,4′-methylene-bis(phenylisocyanate) [OCNC₆H₄CH₂C₆H₄NCO]; and (4) a polyimide based on diaminophenylindane and a dicarboxylic anhydride such as carbonyldiphthalic anhydride [OC₆H₄(CO)₂COC₆H₄(CO)₂]. Thermoset polyimides are produced in condensation polymers that possess reactive terminal groups capable of subsequent cross-linking through an addition reaction. Typical applications for thermoplastic and thermosetting polyimides are transportation and electronics. Can be bonded after plasma treatment using most epoxies.

Polyphenylene Oxide, Modified
Engineering thermoplastic resins produced by the oxidative coupling of 2, 6-dimethylphenol [(CH₃)₂C₆H₃OH] (xylenol), then blended with impact polystyrene. Typical applications are found in electrical/electronic uses, business machine parts, appliances, and automotive parts. Can be bonded with solvents or epoxies. Adhesion can be enhanced greatly after plasma treatments.

Polyphenylene Sulfide
Engineering thermoplastic resins produced by the reaction of p-dichlorobenzene [C₆H₄CI₂] with sodium sulfide [Na₂S]. The major use for polyphenylene sulfide is in electrical/ electronic parts and automotive parts. After plasma treatments, this material bonds effectively with most epoxies.

Polypropylene
Thermoplastic resins made by polymerizing propylene [CH₃CHCH₂] and in the case of copolymers with monomers, with suitable catalysts, generally aluminum alkyl and titanium tetrachloride mixed with solvents. The monomer unit in polypropylene is asymmetric and can assume two regular geometric arrangements: isotactic, with all methyl groups aligned on the same side of the chain, or syndiotactic, with the methyl groups alternating. All other forms, where this positioning is random, are called atactic. Commercial polypropylene contains 90-97% crystalline or isotactic PP with the remainder being atactic. Most processes remove excess atactic PP. This by-product is used in adhesives, caulks, and cablefilling compounds. Major applications of commercial PP are found in packaging, automotive, appliance and carpeting markets. This material can be bonded effectively using UtraFlon Bond-X 1606.

Polystyrene
High molecular weight thermoplastic resins produced generally by the free-radical polymerization of styrene monomer [C₆H₅CHCH₂] which can be initiated by heating alone but more effectively by heating in the presence of free-radical initiator (such as benzoyl peroxide [(C₆H₅CO)₂O₂]. Typical processing techniques are modified mass polymerization or solution polymerization, suspension polymerization, and expandable beads. Major markets for polystyrene are in consumer and institutional products, electrical/electronic uses, and building/ construction. Typically there are no issues bonding this material. But, plasma treatments have been used to enhance wettability of the material.

Polyurethanes
A large family of polymers based on the reaction product of an organic isocyanate with compounds containing a hydroxyl group. The commonly used isocyanates are toluene diisocyanate (TDI) [CH₃C₆H₃(NCO)₂], methylene diphenyl isocyanate (MDI) [OCNC₆H₄CH₂C₆H₄NCO], and polymeric isocyanates (PMDI), obtained by the phosgenation of polyamines derived from the condensation of aniline [C₆H₅NH₂] with formaldehyde (HCHO]. Polyols (with hydroxyl groups) are macroglycols which are either polyester or polyether based. Polyurethane elastomers and resins take the form of liquid castings systems thermoplastic elastomers and resins, microcellular products, and millible gums. Typical applications are found in the automotive industry. Polyurethane foams are widely used in transportation, furniture, and construction markets. Can be bonded effectively using acrylic adhesive or urethane adhesive. Adhesion can be improved greatly after plasma treatment.

If you have any questions about the materials above, Ask The Experts – or visit TriStar.

The last installment is almost here…

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.