Tech Talk Blog

A polymer is a very large molecule (macromolecule) composed of many small repeating molecular units (monomer). Polymers are formed from atoms that are capable of multiple covalent bonds. Such as the carbon atoms in ethylene CH2=CH2 molecule. Molecules with this type of bonding are said to be unsaturated. These compounds tend to keep this structure yet will readily react (under heat and pressure) to form more stable single bond structures; they will form a saturated compound. For example, ethylene will react to form polyethylene [-CH2-CH2-’]n . The [n] signifies the number of repeating units in the polymer backbone. This number can be from 1000 to ~300,000 units. The polyethylene material will have different properties based on the number of repeating ethylene monomer units.

From this simple compound, substitutions can be made to provide different properties. When one substitution is made the compound is a vinyl monomer. When two substitutions are made the compound is a vinylidene monomer. As more substitutions are made other compounds are created.

To recap, polymers are formed through chemical reactions under heat and pressure. Additives, ingredients, and conditions are designed to control how the polymer is formed and desired properties. This process is called polymerization. Polymerizing one kind of monomer will create a homopolymer as in polyethylene or polypropylene.

Visit TriStar to learn even more about polymers – or if you have a specific questions, Ask The Experts right away!

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!

It is more a standard than an exception to bond dissimilar materials in industry these days. Many adhesive manufactures have responded with a variety of liquid treatments to facilitate this trend. Though many of these primers work well, they have safety, shelf-life, and disposal issues. So, what now!

Plasma combines with aqueous (water) based post treatments provide a broad range of environmentally safe and stable surface activation primers. The plasma and corona pre-treatments open the types or polymers that can be primed for the specific chemistry to react with a particular adhesive or paint like rubber to metal. If you would like to improve your current process of metal treatment prior to rubber overmolding or polymer treatment prior to adhesive dispensing, then this technique should be tested. If you have a specific question about your application, Ask The Experts.