Moisture absorption temperatures

Nylon 6 and 6/6 possess the maximum stiffness, strength, and heat resistance of all the types of nylon. Type 6/6 has a higher melt temperature, whereas type 6 has a higher impact resistance and better processibility. At a sacrifice in stiffness and heat resistance, the higher analogs of nylon are useful primarily for improved chemical resistance in certain environments (acids, bases, and zinc chloride solutions) and for lower moisture absorption. 

A combination of excellent chemical and mechanical properties at elevated temperatures results in rehable, high performance service to the chemical processing and related industries. Chemical inertness, heat resistance, toughness and flexibiUty, stress-crack resistance, excellent flex life, antistick characteristics, Htfle moisture absorption, nonflammability, and exceptional dielectric properties are among the characteristics of these resins. 

Although thermal performance is a principal property of thermal insulation (13—15), suitabiHty for temperature and environmental conditions compressive, flexure, shear, and tensile strengths resistance to moisture absorption dimensional stabiHty shock and vibration resistance chemical, environmental, and erosion resistance space limitations fire resistance health effects availabiHty and ease of appHcation and economics are also considerations. 

In addition to time-related effects, the soUd-state physical properties are also affected by adsorbed water, which functions as a plasticizer. Water pickup is affected by the nature of the cation, with sodium ionomers absorbing about 10 times the level of the zinc equivalent (6) under the same conditions. Drying must be carried out at temperatures below 100°C and is therefore a slow process. In commercial practice, ionomers are suppUed dry, and techniques have been developed to minimize moisture absorption during processing. 

The hygroscopic and humectant properties of com symps are of great importance in many apphcations. Depending on the type of symp and on the specific conditions of temperature and humidity, the products may either resist or facihtate moisture loss or moisture absorption. The abihty to attract moisture or retard its loss increases with increasing DE value. Prevention of moisture pickup is more characteristic of symps having low DE values. 

The outer packaging must protect the tea from light and moisture absorption. Polypropylene or coated ceUophane outer wraps for paper board tea packages provide a barrier to loss of tea aroma and retard permeation of oxygen and foreign flavors. Low temperature improves storage stabiHty. Properly packaged and stored teas retain acceptable flavor for about a year. 

Comfort. In the past, the evaluation of fabric or garment comfort has been a subjective process influenced by such variables as temperature, insulating efficiency, moisture absorption, drying speed, softness, bulk, fabric constmction, and air permeability. Human factors must also be considered. 

The highly polar nature of the TGMDA—DDS system results in high moisture absorption. The plasticization of epoxy matrices by absorbed water and its effect on composite properties have been well documented. As can be seen from Table 4, the TGMDA system can absorb as much as 6.5% (by weight) water (4). This absorbed water results in a dramatic drop in both the glass transition temperature and hot—wet flexural modulus (4—6). 

The nylons are hygroscopic. Figure 18.16 shows how the equilibrium water absorption of different nylons varies with humidity at room temperature. Figure 18.17 shows how the rate of moisture absorption is affected by the environmental conditions. 

Nonmetallic materials should have the following desirable characteristics low moisture absorption, resistance to microorganisms, stability through temperature range, resistance to flame and arc, freedom from out-gassing, resistance to weathering, and compatibility with other materials. 

Aminos. There are two basic types of amino plastics - urea formaldehyde and melamine formaldehyde. They are hard, rigid materials with good abrasion resistance and their mechanical characteristics are sufficiently good for continuous use at moderate temperatures (up to 100°C). Urea formaldehyde is relatively inexpensive but moisture absorption can result in poor dimensional stability. It is generally used for bottle caps, electrical switches, plugs, utensil handles and trays. Melamine formaldehyde has lower water absorption and improved temperature and chemical resistance. It is typically used for tableware, laminated worktops and electrical fittings. 

Good mechanical and electrical properties rigidity fair creep behaviour fatigue resistance low moisture absorption broad range of continuous use temperatures -60°C up to 130°C UHF transparency. 

Good ratios for cost versus mechanical and electrical properties fair creep resistance at room temperature low moisture absorption fair heat and cold behaviours moisture and hot-water resistances low shrinkage. 

The effect of the type and level of initiator on polymerization time, monomer conversion, and polymer molecular weight, the effect of polymerization temperature on the crystallization behavior of the polyamide generated, and the role of a higher lactam like laurolactam on the moisture absorption characteristics of the copolymers are discussed in our previous publication [23]. 

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