Phase Changing Material

PCM - Definition

Substances that undergo the process of phase change are also known as phase change materials (PCMs).

These materials store, release or absorb heat as they oscillate between solid and liquid form.

Giving off heat as they change to a solid state and absorbing it as they return to a liquid state.

PCM - DevelopmentIN 1970-80 NASA’s Space Research included considerable research and development on new materials that could protect delicate instruments in space from the temperature extremes they encountered.

NASA used PCMs on the Lunar Rover and Skylab projects in the

A NASA study identified more than 100 PCMs. Some - including pure lithium chloride - are being used for heat management of electronics, telecommunications and microprocessor equipment.

Lithium chloride, however, is not suitable for normal textile applications.

In 1987, (Triangle R&D), demonstrated the feasibility of incorporating PCMs within textile fibers, and were issued a patent in 1994.

Materials used in this work included

Paraffinic hydrocarbons - such as eicosane; and Plastic crystals - such as 2,2-dimethyl-1,3-propanediol (DMP) and

2-hydroxymethyl-2-methyl-1,3-propanediol (DMP).

When plastic crystals absorb thermal energy, the molecular structure is temporarily modified without changing the phase of the material. The thermal properties can be optimized by the choice of the paraffinic hydrocarbon.

Compounds with a higher number of carbon atoms have higher temperature stability.

The patent issued to Triangle R&D on the inclusion of PCM microcapsules within a fiber covers a broad range of fibers including polyester, nylon, acrylics and modacrylics.

PCM - Development

PCM - DevelopmentThe incorporation of PCMs within a fiber requires first that the PCM be microencapsulated.

In order to produce a microencapsulated PCM, some of the following criteria had to be met•    particle size; •    uniformity of particle size; •    stability to mechanical action and chemicals; and •    core-to-shell ratio, with PCM content as high as possible.

In the mid- to late 1980s, work on temperature-adaptable fabrics was undertaken at the US Department of Agriculture's Southern Regional Research Center (SRRC) in New Orleans.

The work was based on the durable binding of polyethylene glycol to cotton and cotton/polyester blends using poly-functional crosslinking agents and acid catalysts. The resultant products were designated "Polytherm" fabrics. The action of the polyethylene glycol polymer complex as similar to a helix that coils and uncoils and acts like a thermal spring.

Frisby Technologies Inc., The company's business was based on sales of its thermal management products Thermasorb® and ComforTemp®.

Frisby developed and patented gel-coated microcapsule technology for the preparation and application of thermal management materials.

SteeleVest® cooling vests.These vests, worn by workers facing extreme heating conditions in industrial and military environments, can provide up to four hours of cooling.

Thermocules® is the name for its PCM material that is applied as a matrix coating on fabric. This type of coating allows the fabric to maintain air permeability.

•    lifestyle apparel - smart fleece vests, men's and women's hats, gloves and rainwear; •    outdoor sports apparel - jackets and jacket linings, boots, golf shoes, running shoes, socks, and ski and snowboard gloves; •    bedding - mattresses, mattress pads, pillows and comforters; and •    automotive seating.

PCM - Development

PCM - Working ConceptWhen the encapsulated PCM is heated to the melting point, it absorbs heat energy as it moves from a solid state to a liquid state.

This phase change produces a temporary cooling effect in the clothing layers (Figure 1).

The heat energy may come from the body (e.g. when the wearer first dons the garment) or from a warm environment.

Once the PCM has completely melted, the storage of heat stops.

If the PCM garment is worn in a cold environment where the temperature is below the PCM's freezing point and the fabric temperature drops below the transition temperature, the microencapsulated liquid PCM will change back to a solid state.

This generating heat energy and a temporary warming effect (Figure 2).

The developers claim that this heat exchange produces a buffering effect in clothing, minimizing changes in skin temperature and prolonging the thermal comfort of the wearer.

PCM - Working Concept

PCM - Working Concept

The clothing layer(s) containing PCMs must go through the transition temperature range before the PCMs will change phase and either generate or absorb heat.

Consequently, the wearer has to do something to cause the temperature of the PCM fabric to change.

PCMs are a transient phenomenon.

They have no effect under steady-state thermal conditions.