Image Credit: 3M Industrial Adhesives & Tapes Canada | Dow Automotive Systems | BJB Enterprises, Inc.
Foams and foam materials are made from low density elastomers, plastics, and other materials with various porosities. They are used in a variety of architectural, industrial, medical, and consumer applications.
There are six basic types of foams and foam materials:
- Open cellular
- Closed cellular
Open cellular foams have interconnected pores or cells and are suitable for filtration applications. Closed cellular foams do not have interconnected pores or cells, but are useful for buoyancy or flotation applications. Flexible foams can bend, flex or absorb impacts without cracking or delaminating. Reticular foams have a very open structure with a matrix consisting of an interconnecting network of thin material strands. Rigid foams feature a matrix with very little or no flexibility. Syntactic foams consist of rigid microspheres or glass micro-balloons held together by a plastic or resin matrix.
Available Foam Materials
Foams and foam materials are available in a variety of forms. Some products contain metal, metal alloy or ceramic materials. Others contain plastics, polymers, elastomers, thermoset plastics, thermoset resins, or thermoplastics.
Casting resins are plastic or elastomer compounds used to cast parts or molds, or form structures in place. They usually consist of two part (A + B) systems where A is the resin and B is the catalyst or hardener. Casting resins are available as spray foams, froth packs and pourable materials.
Molding grade resins are also available, but in the form of pellets. These plastic and elastomer products are suitable for fabricating parts by injection molding, compression molding, blow molding or film extrusion, reaction injection molding (RIM), and resin transfer molding (RTM).
Stock shapes for foams and foam materials include bars, boards, blocks, buns, film, rods and sheets.
Foam Chemical Systems
There are many chemical systems for foams and foam materials.
- Acrylonitrile-butadiene-styrene (ABS) is a hard, rigid, thermoplastic polymer that provides good chemical and creep resistance.
- Acrylics provide excellent environmental resistance and fast-setting times compared to other resin systems.
- Epoxy resins exhibit high strength and low shrinkage during curing.
- Fluoropolymers are used in applications that require superior chemical resistance.
- Styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS) are used in pressure sensitive adhesive applications.
- Synthetic rubbers or elastomers are based on a variety of systems such as silicone, polyurethane and neoprene.
- Nitrile rubber provides good resistance to petroleum hydrocarbons and fuels.
- Plastics or elastomers formed from natural or plant-based raw materials such as natural rubber (polyisoprene) or vulcanized fibre are also available.
- Water-based and water-borne resins and latex materials do not contain volatile organic compounds (VOCs).
- Chemical systems for foams and foam materials include ethylene copolymer, expanded polyethylene, polycarbonate, polyester, polyether, polyetherimide, polyimide, polyolefin, polypropylene, phenolic, polyurea, and vinyl.
Video Credit: BJB Enterprises, Inc.
Important specifications for foams and foam materials include:
- Bulk density
- Tensile strength
- Tensile modulus
- Tear strength
- Use temperature
- Thermal conductivity
- Dielectric strength
Bulk or apparent density depends upon the theoretical density of the foam and its actual porosity after packaging. Tensile strength is the maximum amount of stress required to fail or break the foam under tension loading conditions. Young’s modulus or the modulus of elasticity is a material constant that indicates the variation in strain produced under an applied tensile load.
Elongation is the percent deformation occurring during a tensile or other mechanical test. Thermal conductivity is the linear heat transfer per unit area through a material for a given applied temperature gradient. Dielectric strength is the maximum voltage field that the material can withstand before electrical breakdown occurs.
ASTM D3574 - STANDARD TEST METHODS FOR FLEXIBLE CELLULAR MATERIALS - SLAB, BONDED, AND MOLDED URETHANE FOAMS
ASTM D6826 - STANDARD SPECIFICATION FOR SPRAYED SLURRIES, FOAMS AND INDIGENOUS MATERIALS USED AS ALTERNATIVE DAILY COVER FOR MUNICIPAL SOLID WASTE LANDFILLS
ASTM F2038 - STANDARD GUIDE FOR SILICONE ELASTOMERS, GELS, AND FOAMS USED IN MEDICAL APPLICATIONS PART I - FORMULATIONS AND UNCURED MATERIALS