Relative humidity, thermoplastic

In Table 1, the moisture uptake of cured and uncured Navy P3-2300-PE resin after 24 hours of immersion is compared to a number of other high-temperature polymer resins. The moisture uptake of the Navy P3 oligomer is nearly identical to that of the commercial P3 thermoplastic. Other commercial thermoplastics, such as poly(ether ether ketone), with very similar chemical compositions, exhibit similarly low levels of moisture uptake. On the other hand, the Navy P3 resins absorbs about 85% less water than the commercial polyimide Kapton HN. Since thermosetting phenyl ethynyl end-capped polyimides have moisture uptake characteristics that are similar to Kapton HN, with around 3% weight gain on exposure to 95% relative humidity (77), void-free composites based on Navy P3 resins should exhibit greatly reduced moisture uptake compared to those based on thermosetting polyimides. 

R. J. Gardner and J. R. Martin, Effeet of relative humidity on the mechanieal properties of thermoplastic polyesters, in 37th Antec SPE, 1979, pp. 831-834. 

Figure 1. The effect of relative humidity (RH) on mechanical properties [stress-strain curves] of at thermoplastic starch polymer.

Table 1. Diffusivity of Water at different Temperatures in Thermoplastic Starch Polymers pre-stored at various relative Humidities...

Such materials, however, are not appropriate for packaging films, and regenerated cellulose or cellophane was the first practical glassy film to find large scale use in packaging (36). Cellophane is an excellent gas barrier in the dry state however, it is sensitive to moisture and loses barrier capability at high relative humidities (4,23). Moreover, it is not thermoplastic or heat sealable, so replacements were clearly desirable. 

The time required for conditioning is typically 3 hours (ISO 471) or 4 hours (ISO 291) for temperature alone, but up to a minimum of 96 hours where temperature and humidity are controlled. Where temperature and relative humidity are controlled, wide variations in conditioning time between types of material are ob.served. For example. 88 hours is a widely used minimum for thermoplastics, but cellular materials and fabrics coated on one side only with a polymer film may only need to be conditioned for a minimum of 16 hours. Reference should be made to the specific test method of intere.st to ensure compliance with its requirements. 

The environment in which the sport is taking place can also pose some constraints for example, the development of sensors for wet sports, impact sports or sports taking place in extreme temperature requires additional consideration for the system s robustness and stability. Further, local temperature, humidity and pH levels also change during physical exercise and can affect some sensors. For example, Cochrane et al. (2007) demonstrated how the electrical performance of their sensor material, a thermoplastic elastomer composite, was affected by high humidity. After 50% relative humidity, resistance increases rapidly with humidity. They attributed it to the carbon black nanoparticles of the composite, which are sensitive to water. At high humidity, temperature also had a small effect on resistance. Munro et al. (2008) also found that while their strain sensors were able to provide valid and reliable data compared to a video-based motion analysis system, the consistency of the feedback was affected by enviromnental conditions. 

Polybenzimidazole (PBI) is an amorphous thermoplastic with a high glass transition temperature (T ) of 425°C-436°C (Li et al. 2003c) and demonstrates excellent thermal, chemical, and mechanical stabilities (Zhang et al. 2008.). Moreover, PBI exhibits a good protonic conductivity even at low relative humidity (Bouchet and Siebert 1999). PBI has to be doped with several acids, such as sulfuric acid and phosphoric acid, in order to improve its conductivity. The acid acts as both donor and acceptor in proton transfer and therefore allows for proton migration along the anionic chain. PBI also showed lower methanol permeability (Pivovar et al. 1999). 

Storage of water in micro-damaged regions. The rate at which a composite material exposed to moisture absorbs water reduces with time until eventually the liqtiid content reaches an equilibrium (saturation) level. The time taken for a composite laminate of a given thickness to attain this equilibrium moisture concentration depends on the temperature and relative humidity of the environment. Typically, synthetic fiber/thermoset matrix composites have saturation limits ranging from 1 to 2%, while synthetic fiber/ thermoplastic matrix composites have lower limits of 0.1 to 0.3% [15]. 

Ihe latter films are plasticized by glycols and water to overcome their brittleness and are transparent, colorless and of moderate crystallinity. Ihey were very widely used for packaging but have been substantially replaced by synthetic thermoplastics, especially polypropylene. They have very high permeability to moisture and, especially when dry, very low permeability to permanent gases. Their moisture content varies greatly with their environment, reaching approximately 50% at 100% relative humidity. Not surprisingly, this causes many of their properties to vary considerably—so summarized values must be treated with considerable caution [35]. 

Polymeric antistatic agents have been employed in textile fibres. loni-cally conductive copolyethers such as ethylene oxide/propylene oxide copolymers and other similar polymers are examples. Polyoxyethylene derivatives with high electrical conductivities caused by proton migration are not highly dependent on relative humidity and have found some use in thermoplastics. 

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