Polyamide thermal and chemical properties

Dielectric constant and dielectric loss, by contrast, along with the increase of water absorption increases, this is because water is the main impurity in the PA, the presence of water will increase its polarizability. Therefore, PA not work well as a high frequency and electrical insulating materials in wet or humid conditions. In the shaping of PA bibulous rate is first encountered problems, bibulous rate is high not only makes the melt viscosity drops parts, injection molding processing products, silver surface bubbles, markings, and products of mechanical properties and electric properties are significantly reduced. Therefore, molding resin must be dry before, bibulous rate is reduced to zero. Less than 2%. To avoid oxidation, usually using the vacuum drying method, drying temperature is 80 - 100 ℃, 6 - drying time 10h。

Tm depends on the molecular chain of different PA in the number of continuous methylene and methyl odd even. PA although higher melting point, but the long-term use of temperature is not high, should not be more than 100 ℃, usually at about 80 ℃. If under the temperature of 100 ℃ above contact with oxygen for a long time can cause the surface slowly hot oxygen degradation, products gradually appear brown, loss of performance. To improve the heat resistance of PA, aromatic PA was developed in the 1960 s, the long using temperature is 200 ℃.

PA weatherability, products by sunlight in indoor or not use its performance change with the extension of time is not big, but directly exposed to the atmosphere or under the action of heat oxygen is easy to aging, lead to products surface discoloration, mechanical performance degradation, usually add carbon black, amine and phenolic stabilizer can obviously improve the weatherability, also can make the heat resistance is improved. PA under the condition of low temperature and low humidity, is a good electrical insulator, but temperature and humidity increases, the deterioration of insulation performance, is the main PA chain containing polarity amide easy bibulous may go.

5 - PA is linear expansion coefficient of metal Seven times. 1/400 of 1/200 of the thermal conductivity of carbon steel, brass, and used as wear-resistant materials, considering the friction heat, should be used with metal, or use oil lubrication, avoid heat accumulation. In addition, adding copper powder or graphite can improve the cooling ability of PA. Most of the PA with self-extinguishing, although a few varieties with combustible, but the flame propagation speed is slow.

PA in resistance to dilute acid, weak alkali, and most of the salt at room temperature, but the strong acid and a high concentration of acid and strong oxidizer can make obvious erosion. Acids of damage will cause macromolecular chain rupture, make the products surface produces different depth of crack or reticular cracks, such as soak in 20 - or PA6 PA66 50 g/L in the concentration of hydrochloric acid, the crack of after a few months. So in actual use, if the organic acid and oxidant, best carefully test first. General PA amide group distribution density, the greater the resistance to acid.

fiber has become an important means to improve PA mechanical strength, fatigue strength greatly increased, not only enhanced the impact strength, hardness, creep resistance and heat resistance and dimensional stability is greatly improved, to further expand the scope as application of the engineering plastics. PA is a crystalline polymer, molecular inter-atomic forces, high melting point. Narrow range of melting temperature of the PA, a melting point called clear, usually in the 180 - Between 280 ℃ and vary with different varieties and structure.

the PA good solvent resistance and ability of hydrocarbon, oil and general solvent. Good oil resistance is an important characteristic of PA, its are in inert the mineral oil, vegetable oil and grease. But water and alcohol and similar compounds can make the PA produces swelling, can form hydrogen bonds with some solvent at room temperature was dissolved, such as PA soluble in formic acid, glacial acetic acid, phenol, cresol and methanol solution of calcium chloride. PA injection tooling industry often use this feature of their products are adhesive.

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