TPE can be extruded to form self-supporting films for the lamination of apparel fabrics. tpe films can provide protection while ensuring gas flow, an indicator that can be measured by breathability. The usual trade use for the development of water and moisture permeable films is in the form of microporous forms such as expanded stretch PTFE films, various polyolefin films, and wet process polyurethanes. In fabric applications, TPE non-porous films have application advantages, such as abrasion resistance and physical properties. When the film is laminated to the fabric, small molecules such as water vapor can pass through the film by dissolution/diffusion. "Breathable" polymers are materials that have a high permeability to water vapor, not to airborne components such as oxygen and carbon dioxide, and in general, the higher the active ingredient in the polymer, the higher the permeability.
The transport behavior of water vapor molecules in a dense film is generally carried out by molecular diffusion (cf. absorption-diffusion model), using the vapor pressure difference between the two sides to generate a driving force. In order to reduce the transfer resistance, the film should have high permeability and low thickness, but the lower the film thickness is not better in terms of the physical properties of the film. The important parameters of microweather between the skin and the film are temperature and humidity. In order to maintain a stable thermodynamic balance between body temperature and the environment (as a definition of comfort). The heat generated by human activity should be i.e. the heat of the realm. The main principle of heat loss, especially during physical activity, is mainly evaporation of water and transport of steam to the environment. At the time of physical activity, the evaporation of 800 grams of water per hour from the human body corresponds to a heat loss of 1800 KJ, about 80% of the heat generated.
There are many factors that influence the permeability and respiratory properties of polymers. For example, the nature of the material's hydrophilicity, crystallinity, and filler content can all affect the polymer's transmission of vapor. tPEs are often used in medical materials as AB-structured malignant multistage copolymers. Elastomeric materials with acyl, urethane, and ester-based hard segments often provide usable mechanical properties that make them usable for the manufacture of films. Permeability is improved by manipulating the backbone of the TPE molecule, e.g., by normalizing the hydrophilic component to the affinity of the polymer for water.
In segmented TPE materials, permeation occurs mainly in the rubbery, elastic soft segment phase rather than through the hard segment phase. Therefore, the permeation properties are opposed to the variation of the hard segment content. Usually, the soft segment content mainly determines the water vapor permeability. The basic polyether soft segments used for TPE films are mainly PEO and PEG or PPO/PEO copolymers, but PTMG is also used. Complete PPO chain segments are basically not used in vapor permeable TPEs. Usually a mixture of different soft segments is used to balance the physical properties: e.g. PEO is more hydrophilic, while PTMG has excellent mechanical properties and does not swell as much as the former. Increasing the CH2/O2 ratio reduces the compatibility of the soft and hard segments. The molecular weight of the hydrophilic chain segment is in the same order of magnitude as other polyether-based TPEs, both (600-4000 g/mol).
Synthetic TPEs have the highest permeability, close to well-known hydrophilic materials such as cellulose and polyvinyl alcohol. One disadvantage of using PEO is that the film surface is too sticky. According to the absorption-diffusion model, vapor permeability is a function of the amount of permeate and the rate of diffusive motion. The high chain segment motion, confirmed by the glass state temperature of all PEO soft segments is 0°C, which promises a high diffusion coefficient. It is usually assumed that the high moisture transmission rate is related to the continuous soft segment phase. Water uptake is highly correlated with the soft segment PEO content and also with the soft segment molecular weight. Increasing the molecular weight of the soft segment while advancing the water absorption rate is believed to be related to the degree of separation of the soft and hard segments. Soft segments with low molecular weight usually yield films with strong physical properties. The high molecular weight soft segments line up into more pronounced PEO micro-regions, but the hard segments weaken and are able to absorb large amounts of water. The increase in water uptake usually shows an exponential increase, which can be explained by the physical cross-linking. These crosslinks give the swelling limits of the hydrophilic microregions. At low PEO content, the absorbed water is bound to PEO chain segments; above a certain PEO content, free water increases.
The melting point of vapor permeable TPE films is mainly determined by the type of hard segment. The high melt temperature period is seen in high temperature processes to provide thermal stability, such as laminating films, waterproof fabrics, laminated films. pa12 has 12 carbons on its repeating unit, up to most TPU hard segments provide a melting point of 175°C or below, while some polyester type TPEs have a melting point of up to 200°C. A range of important physical properties such as tensile strength, abrasion resistance are also largely determined by the hard segment, such as bonding A range of important physical properties such as tensile strength and abrasion resistance are also largely determined by the hard section, for example, the combination of nitrogen-containing PA12 and TPU hard sections is usually stronger.