Foam rubber (also known as cellular rubber, sponge rubber, or expanded rubber) is rubber that has been made with a foaming agent so that its structure is an air-filled matrix. Commercial foam rubber is generally made of synthetic rubber, natural latex, or polyurethane. Latex foam rubber, used in mattresses, is well known for its endurance. Polyurethane is a thermosetting polymer that comes from combination of methyl di-isocyanate and polyethylene and some chemical additives. [1]
Foam rubber was first made in 1929, by E. A. Murphy [2] and Eric Owen, two research chemists at Dunlop Rubber, who used whipped latex. In 1937, isocyanate-based materials were first used to make foam rubber. After World War II, styrene-butadiene rubber replaced many natural types of foam. Foam rubber has been used commercially for a wide range of applications since the 1940s.
Polyether polyurethane rubber was discovered and patented in the 1950s, by Charles C. Price. [3] Polyurethane foams now make up over 90%, by weight, of the entire market for polyurethanes. The largest amount of polyurethane is used by these in construction, transportation, home furniture, noise and vibration reduction, and carpet. Construction uses 27% of polyurethane, and transportation uses 21%. Flexible foam is the leading use, at 44% of total volume; rigid foam makes up 28% of the United States market. [4]
Rates of polymerization can range from a few seconds to many minutes. Fast-reacting polymers have short cycle-periods and require machines to mix the reacting agents. Slow polymers may be mixed by hand; because hand-mixing takes a long time, industrial applications tend to use powered mixers. Ways of processing the product include spraying, open pouring, and molding, among others.
The main physical properties of foam rubber are light weight, buoyancy, cushioning, thermal and acoustic insulation, impact damping, and cost reduction. [5] Crosslinking technology is used in the formation of EVA based foams, including LLDPE, LDPE, HDPE, PP, and TPE. Crosslinking is the most important characteristic in the production of foam rubber to obtain the best possible foam expansion and physical properties. Crosslinking is chemical bonding between polymer chains, and is used in foam-rubber manufacturing to stabilize bubble expansion, enhanced resistance to thermal collapse, and improve physical properties. [6]
Because of the variety in polyurethane chemistries, it is hard to recycle foam rubber using a single method. Reusing slab stock foams for carpet backing is how most recycling is done. This method involves shredding the scrap and bonding the small flakes together to form sheets. Other methods involve breaking the foam down into granules and dispersing them into a polyol blend to be molded into the same part as the original. The recycling process is still developing for foam rubber and the future may unveil new, easier recycling. [7]
Vulcanization is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to include the hardening of other (synthetic) rubbers via various means. Examples include silicone rubber via room temperature vulcanizing and chloroprene rubber (neoprene) using metal oxides.
Polyurethane refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane term does not refer to the single type of polymer but a group of polymers. Unlike polyethylene and polystyrene polyurethanes can be produced from a wide range of starting materials resulting various polymers within the same group. This chemical variety produces polyurethanes with different chemical structures leading to many different applications. These include rigid and flexible foams, and coatings, adhesives, electrical potting compounds, and fibers such as spandex and polyurethane laminate (PUL). Foams are the largest application accounting for 67% of all polyurethane produced in 2016.
Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to air and water vapor and has a relatively low melting point. Polystyrene is one of the most widely used plastics, with the scale of its production being several million tonnes per year. Polystyrene is naturally transparent, but can be colored with colorants. Uses include protective packaging, containers, lids, bottles, trays, tumblers, disposable cutlery, in the making of models, and as an alternative material for phonograph records.
A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst. Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.
Wood fibres are usually cellulosic elements that are extracted from trees and used to make materials including paper.
In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups. The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, three and four hydroxyl groups are diols, triols, and tetrols, respectively.
Methylene diphenyl diisocyanate (MDI) is an aromatic diisocyanate. Three isomers are common, varying by the positions of the isocyanate groups around the rings: 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI. The 4,4′ isomer is most widely used, and is also known as 4,4′-diphenylmethane diisocyanate. This isomer is also known as Pure MDI. MDI reacts with polyols in the manufacture of polyurethane. It is the most produced diisocyanate, accounting for 61.3% of the global market in the year 2000.
Polyisocyanurate, also referred to as PIR, polyol, or ISO, is a thermoset plastic typically produced as a foam and used as rigid thermal insulation. The starting materials are similar to those used in polyurethane (PUR) except that the proportion of methylene diphenyl diisocyanate (MDI) is higher and a polyester-derived polyol is used in the reaction instead of a polyether polyol. The resulting chemical structure is significantly different, with the isocyanate groups on the MDI trimerising to form isocyanurate groups which the polyols link together, giving a complex polymeric structure.
Thermoplastic elastomers (TPE), sometimes referred to as thermoplastic rubbers (TPR), are a class of copolymers or a physical mix of polymers that consist of materials with both thermoplastic and elastomeric properties.
Foam latex or latex foam rubber is a lightweight form of latex containing bubbles known as cells, created from liquid latex. The foam is generally created though the Dunlop or Talalay process in which a liquid latex is foamed and then cured in a mold to extract the foam.
A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied when the blown material is in a liquid stage. The cellular structure in a matrix reduces density, increasing thermal and acoustic insulation, while increasing relative stiffness of the original polymer.
Building insulation materials are building materials that form the thermal envelope of a building. As thermal insulation they reduce the heating energy requirement or the cooling load of buildings ; they can also provide soundproofing.
Spray foam is a chemical product created by a chemical reaction of two component parts, commonly referred to as side A and side B. Side A contains very reactive chemicals known as isocyanate. Side B contains a polyol, which reacts with isocyanates to make polyurethane, and a mixture of other chemicals, including catalysts, flame retardant, blowing agents and surfactants. These react when mixed with each other and expand up to 30-60 times its liquid volume after it is sprayed in place. This expansion makes it useful as a specialty packing material which forms to the shape of the product being packaged and produces a high thermal insulating value with virtually no air infiltration.
Rigid panel insulation, also referred to as continuous insulation, can be made from foam plastics such as polyurethane (PUR), polyisocyanurate (PIR), and polystyrene, or from fibrous materials such as fiberglass, rock and slag wool. Rigid panel continuous insulation is often used to provide a thermal break in the building envelope, thus reducing thermal bridging.
Resin casting is a method of plastic casting where a mold is filled with a liquid synthetic resin, which then hardens. It is primarily used for small-scale production like industrial prototypes and dentistry. It can be done by amateur hobbyists with little initial investment, and is used in the production of collectible toys, models and figures, as well as small-scale jewellery production.
Polyaspartic ester chemistry was first introduced in the early 1990s making it a relatively new technology. The patents were issued to Bayer in Germany and Miles Corporation in the United States. It utilizes the aza-Michael addition reaction. These products are then used in coatings, adhesives, sealants and elastomers. Pure polyurea reacts extremely quickly making them almost unusable without plural component spray equipment. Polyaspartic technology utilizes a partially blocked amine to react more slowly with the isocyanates and thus produce a modified polyurea. The amine/diamine or even triamine functional coreactant for aliphatic polyisocyanate is typically reacted with a maleate. Polyaspartic esters (PAE) initially found use in conventional solvent-borne two-component polyurethane coatings.
Polyurethane foam is a solid polymeric foam based on polyurethane chemistry. As a specialist synthetic material with highly diverse applications, polyurethane foams are primarily used for thermal insulation and as a cushioning material in mattresses, upholstered furniture or as seating in vehicles. Its low density and poor thermal conductivity combined with its mechanical properties make them excellent thermal and sound insulators, as well as structural and comfortable materials.
Sulfur vulcanization is a chemical process for converting natural rubber or related polymers into materials of varying hardness, elasticity, and mechanical durability by heating them with sulfur or sulfur-containing compounds. Sulfur forms cross-linking bridges between sections of polymer chains which affects the mechanical and electronic properties. Many products are made with vulcanized rubber, including tires, shoe soles, hoses, and conveyor belts. The term vulcanization is derived from Vulcan, the Roman god of fire.
