2021 Raw Materials, Chemicals, Polymers, and Additives Handbook

Natural Latex

Natural latex is harvested from the Hevea Brasiliensis, a tree native to South America that is harvested on rubber plantations in Southeast Asia. The latex can be used in the latex form or coagulated as so-called “natural rubber.” The latex finds many uses, including adhesives and foam manufacture. Disposable medical gloves have provided a major growth area, but concerns have arisen due to severe latex allergies in some users caused by residual proteins found in the gloves. (See also Natural Rubber.)

Natural Rubber

The most useful elastomer for pressure-sensitive adhesives has proven over the years to be natural rubber, which consists largely of cis-polyisoprene. With a broad molecular weight, ranging anywhere from around 500,000 to 2,000,000, there is much that can be done with natural rubber. There is a twin spread of molecular-weight distribution in natural rubber, and the higher fraction contributes considerably to shear resistance.

Natural rubber is very compatible with many raw materials and offers a good balance of properties when used in a PSA. It is soluble in a variety of aliphatic and aromatic hydrocarbons and chlorinated hydrocarbons, but is insoluble in ketones and alcohols. It is forgiving in that the ratio of natural rubber to tackifier used in formulations is usually non-critical: it takes a change of around 5% before any noticeable change in properties occurs.

As a natural product derived from the latex of the rubber tree, Hevea Braziliensis, there is a reasonable quantity of protein present in natural rubber that acts as a natural preservative. It is available in a wide range of grades.² (See also Natural Latex.)

Phenolic Resins

Specialty resins used in the formulation of adhesives and sealants to add “tack” and improve adhesion. (See also Tackifiers.)

Phenol Formaldehyde

Synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde.

Polyacrylic Rubber

Polyacrylic rubber, sometimes called ACM, is a synthetic rubber that is highly resistant to heat and oils.

Polyamide Resins

Polyamides, commonly known as nylons (formerly a DuPont trademark), were first commercialized in 1939 when DuPont introduced the fibers to make women’s stockings. Polyamides consist of chains of methylene groups linked by amide groups. Synthesis occurs by two routes, either through the condensation of a diamine with a dicarboxylic acid or through the ring opening polymerization of a cyclic lactam. The two most common polyamides are Nylon 6,6 and Nylon 6, which have quite similar properties and are characterized by being very strong, rigid plastics with lubricity, abrasion resistance, heat strength, and chemical resistance. Polyamides are very useful as high-temperature hot-melt adhesives, and they bond well to a range of materials.              

Polyamino Co-Reactant

Polyamino co-reactant resins are solvent-free, amine-functional reactive partners for polyisocyanates.

Polybutadienes

Polybutadiene rubber was first manufactured in Russia and Germany in the 1920s by polymerizing butadiene with sodium. This was called “Buna” rubber. Today most polybutadiene is produced in solution with alkyl lithium catalysts and is used in tire production. Latices of polybutadiene are still manufactured and used in adhesives.

Polybutadiene is a very tacky polymer with a very low glass-transition temperature (Tg) of-79˚C. Latices are used for manufacturing low-temperature pressure-sensitive adhesives for tapes and labels. They are also used as heat-curable adhesives/sealants in the automotive industry.

Polybutadienes, Liquid Hydroxyl-Terminated

Liquid hydroxyl-terminated polybutadienes can offer good transparence, low viscosity, age resistance, low temperature performance, and good process capability.

Polybutenes

Polybutenes are synthetic liquid hydrocarbon polymers made by polymerization of C4 olefins (primarily isobutene) and are available in a wide range of viscosities. By controlling the polymerization conditions, polymer chains of different lengths are manufactured giving a wide range of polybutene grades having different physical properties. Short chain-length polybutenes are free-flowing; medium chain-length polybutenes are sticky with a honey-like consistency, while those with the longest chain length are very tacky, semi-solid materials. (See also Plasticizers and Tackifiers.)

Polychloroprene

Polychloroprene is especially resistant to oil. It was the first synthetic elastomer, or rubber, to be a hit commercially. It was invented by Arnold Collins while working under the same fellow who invented nylon, Wallace Carothers.

Polyester Resins

A versatile synthetic copolymer, polyester resin is the result of a condensation reaction between a glycol and an unsaturated dibasic acid. Polyester resins are viscous liquids and pale yellow in color.

Polyisobutylene

Polyisobutylene is a synthetic rubber, or elastomer. It is the only rubber that is gas impermeable; that is, it is the only rubber that can hold air for long periods of time.

Polyisoprene

A polymer of isoprene.     

Polymers

Polymers is a general term used to describe long-chain natural and synthetic molecules, and describes materials that are commonly called plastics, rubbers, and resins.

Polymers, Hybrid

Hybrid polymers are silane-curing organic polymers that combine the typical advantages of silicones and polyurethanes. Hybrid polymers have low viscosity and therefore do not require the addition of plasticizers, solvents, or a tin catalyst for the production of adhesives and sealants. (Source: www.wacker.com)

Polymers, Silyl-Modified Polyethers (MS Polymers)

Base resins featuring a functionalized polyether backbone with reactive silane terminal groups.

Polymers, Silyl-Modified Polyurethanes (SPUR Polymers)

Base resins featuring a functionalized polyurethane backbone with reactive silane terminal groups.

Polyolefins

Polyolefins are the most important plastics used worldwide and comprise polymers and copolymers of olefins, such as ethylene, propylene, butane, and hexene. The polymers range from rigid plastics like polypropylene and high-density polyethylene to soft, rubbery materials called plastomers, which are intermediates between plastics and rubbers. The so-called thermoplastic olefins (TPOs) are blends of polyolefins like polypropylene with rubbers such as ethylene propylene diene monomer (EPDM) and are very widely used as plastic films in automotive interiors.

Polyols

The term polyol is used quite broadly to describe a short-chain molecule or polymer with two or more alcohol groups. Polyols can comprise hydrocarbon backbones with alcohol functionality, but the two most common types are polyester and polyether polyols. These are used as precursors to acrylic monomers and are used widely in the manufacture of polyurethanes.             

Protein-Based

Protein resins used in structural adhesives come from several sources, such as animal blood, fish, milk, connective tissue, and soybeans. Protein-based adhesives have been used throughout history. Their primary use in modern times is in the production of plywood for interior applications.

Protein-Based, Casein

Casein is obtained from milk by precipitation induced by acids such as lactic acid. Milk-based adhesives are called casein-based adhesives.

Rosin Esters

Rosin esters are modified rosin products that find use predominantly in adhesives as tackifiers and/or process aids in other industries. (See also Tackifiers.)

Rosins

Rosins are resins extracted from several types of pine trees. They can be distilled to remove volatiles like turpentine and polymerized to form a range of resins and oils, which are useful as base materials and tackifiers in solvent-based and hot-melt adhesives, sealants, and coatings. (See also Introduction to Resins.)

Silicon Polymers

Also known as polysiloxanes, synthetic compound made up of repeating units of siloxane combined with carbon, hydrogen, and sometimes other elements.

Silicon Rubbers

The silicon polymer chain consists of silicon and oxygen atoms (siloxane). Typically, silicon rubbers are processed as solid rubber and crosslinked with peroxide.

Silicone Dispersions

Silicones are polymeric materials that have alternating silicon and oxygen atoms in their backbone. They are available in various molecular weights and forms. Emulsions or dispersions in water are used as lubricants and defoamers. Crosslinked polymers are formed using two-component systems or single-component systems that cure with atmospheric moisture. These polymers are high-performance elastomers with very high flexibility and outstanding high-temperature performance. Very highly crosslinked systems are more rigid and are known as silicone resins. The resins are used in high-temperature electrical applications.             

Silicone Resins

Silicone resins are organopolysiloxanes that are an irregular three-dimensional network or principally tri- or tetrafunctional units.       

Styrene Resins

The term styrene resin is sometimes used to describe materials like acrylonitile butadiene styrene (ABS). (See also Introduction to Resins.)

Styrene Resins, Solid

A solid, transparent thermoplastic resin formed by polymerizing styrene.

Styrene Resins, Solution

 (See Styrene Resins and Styrene Resins, Styrene Butadiene Rubber.)

Styrene Resins, Styrene Butadiene Emulsions

(See Styrene Resins, Styrene Butadiene Rubber.)

Styrene Resins, Styrene Butadiene Rubber

A rubber derived from the random copolymerization of styrene and butadiene. Two predominant technologies currently prevail. Solution SBR (styrene butadiene rubber) is polymerized in a hydrocarbon medium. Emulsion SBR polymerization takes place in an aqueous medium and soap as an ingredient in the coagulation process.

Styrene Resins, Styrene Ethylene Butadiene Styrene Rubber (SEBS)

SEBS is a form of thermoplastic elastomer with styrene added.

Thermoplastic Resins

A thermoplastic resin is a polymer that softens when exposed to heat and returns to its original condition when cooled to room temperature. Natural substances that exhibit this behavior are crude rubber and a number of waxes; however, the term is usually applied to synthetics such as polyvinyl chloride, nylons, fluorocarbons, linear polyethylene, polyurethane prepolymer, polystyrene, polypropylene, and cellulosic and acrylic resins. They are distinct from thermoset resins, which cure or crosslink on heating and cannot be resoftened. 

Thermosetting Resins

Thermosets and thermosetting resins are crosslinked polymeric resins cured or set using heat or heat and pressure.

Urethane Resins

A term used to describe polyurethane polymers used in the adhesives, sealants, coatings, and elastomers markets. Urethane resins can be supplied as polyurethane prepolymers, fully reacted thermoplastic polyurethane polymers, or waterborne polyurethane dispersions.

For adhesive applications, polyurethane prepolymers can be moisture cured or cured by combination with a second component containing hydroxyl or amine groups. Fully reacted thermoplastic polyurethane polymers and waterborne polyurethane dispersions are typically heat-activated and bonded with pressure.

Urethane Resins, Films

Film resins used in applications including metal adhesives.

Urethane Resins, One-Component

One-component urethanes are available as solvent-based systems or 100% solid systems. Solvent adhesives consist of a high-molecular-weight hydroxy-terminated polyurethane dissolved in a solvent. The polymer solutions are applied to both surfaces to be bonded and the solvents are allowed to evaporate. The surfaces are then pressed together, often using a heated nip roll.

There are two types of 100% solids adhesives—moisture-cured products and heat-cured products. Moisture-cured products use a liquid isocyanate-terminated polyurethane and can be allowed to cure by atmospheric moisture; in some cases, they are misted with water to speed up the curing. Heat-cured adhesives use blocked isocyanates, where the isocyanate groups are reacted with agents such as e-caprolactam, methylethylketoxime, 3,5-dimethyl pyrazole, and diethyl malonate. The blocking agents are released by heat, thus liberating the isocyanate groups that can then react with hydroxy groups from a polyol. (See also Urethane Resins.)

Urethane Resins, Two-Component

Two-component urethane adhesives consist of two relatively low-molecular-weight components: a polyol and an isocyanate. The components are mixed together and cure to a polyurethane. These types of adhesives are much faster curing than one-component systems. (See also Urethane Resins.)

UV-Curing Resins

UV-curing resins comprise acrylate and methacrylate monomers and oligomers. They are formulated with photoinitiators (chemicals that decompose with the energy from UV or visible light) and cure by free-radical-initiated polymerization. Newer systems involve monomers like cycloaliphatic epoxies and vinyl ethers, which cure by a cationic mechanism initiated by strong acids generated from the UV decomposition of novel ionic salts. UV systems are valuable as very-fast-curing coatings, adhesives, sealants, and gasketing compounds in a range of industries.              

VEGETABLE-BASED

Resins based on vegetables, such as soybeans. (See also Protein-Based.)

Vegetable-Based, Toll Oil Rosin

Rosin acids derived from the kraft process.

Vinyl Resins

(CH₂==CH--),specifically vinyl chloride, vinyl acetate, and similar esters, but also referring more generally to other types of compounds. Polyvinyl chloride (PVC) is a hard, rigid polymer that can be plasticized to make a soft, flexible version. PVC is the second-largest-volume polymer produced in the world (after polyethylene), and its main application areas are in construction (e.g., vinyl siding), furniture, and packaging. The vinyl compounds are highly reactive and polymerize easily.

Vinyl Resins, Polyvinyl Acetate

A type of thermoplastic, polyvinyl acetate is a rubbery synthetic polymer with the structure (C₄H₆O₂)N.

Vinyl Resins, Polyvinyl Alcohol

One material used as both a surfactant and part of a colloid protection system is hydrolyzed polyvinyl acetate (PVAc). The material is either polyvinyl alcohol (PVA) or PVA-co-PVAc. These combinations of surfactants and cellulosic protective colloids optimize properties, provide improved wettability on various surfaces, or have the potential for crosslinking.³ (See also Vinyl Resins.)

Vinyl Resins, Vinyl Acetate Ethylene Emulsions

Ethylene vinyl acetate copolymers (EVAs) are conventionally regarded as those copolymers of ethylene and vinyl acetate where the weight percentage of ethylene in the polymer molecule exceeds that of the vinyl acetate. Adhesive grades generally fall in the range of 14-35% vinyl acetate and have a melt index (a measure of tendency to flow at elevated temperature) in the range of 5-2,500.

The vinyl acetate content and the molecular weight range influence adhesive properties and hot-melt rheology. The higher the ethylene content, the better the specific adhesion to non-polar substrates, such as polyolefins. The polymers higher in vinyl acetate show improved adhesion to polar substrates, such as paper. Lower-molecular-weight polymers yield lower-melt-viscosity hot melts that are easier to process and apply. These also provide better wetting and, thus, improved mechanical adhesion to porous substrates, such as paper and wood. Higher-molecular-weight polymers are used for applications requiring optimum cohesive strength at elevated temperatures and good low-temperature flexibility. (See also Vinyl Resins.)

Vinyl Resins, Vinyl Acetate Polymer Emulsions

Polyvinyl acetate (PVAc) emulsion adhesives are known to the consumer and the industry as “white glue.” In wood bonding with PVAc adhesives, much of the drying of the adhesive takes place by sorption of water by the wood. White glues are widely used in the packaging industry for the manufacture of cardboard and paper bags.³ (See also Vinyl Resins and Polyvinyl Acetate.)