热状态改变
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作者:profed5ca94
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发布时间: 2021-02-02
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1375 次浏览
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高聚物材料的一个重要物性值是“玻璃转化温度”（也称为玻璃转化点）。此特性对材料合理使用有重要意义。结晶性树脂一般有“玻璃状态”、“粘弹状态（橡胶状态）”和“熔融状态”等 3 种状态。
3.1 热状态改变
高聚物材料的一个重要物性值是“玻璃转化温度”（也称为玻璃转化点）。此特性对材料合理使用有重要意义。
结晶性树脂一般有“玻璃状态”、“粘弹状态（橡胶状态）”和“熔融状态”等 3 种状态。随着加热的进行，树脂将从“玻璃状态”转化为“粘弹状态（橡胶状态）”和“熔融状态”。其间的变化点分别称为玻璃转化温度（Tg）和熔点（Tm）。
熔融状态容易理解，但“玻璃状态”和“粘弹状态（橡胶状态）”有什么特点呢？两者均属固体，但分子的自由度不同。在“玻璃状态”下，树脂又硬又脆，而且分子几乎无法运动；而在“粘弹状态”下，虽说树脂的结晶部分无法运动，但非晶部分则可较为自由地运动，从而具有一定的柔软性（可以变形）。就普通橡胶和结晶性树脂而言，由于弹性模量不同，因而有软硬之别，但都可以称为粘弹状态。由此可见，物理性质在玻璃转化温度的前后会发生很大变化。这种变化通常体现在体积、粘性、强度、硬度等方面。这便是玻璃转化点之所以重要的原因。
树脂材料的物理性质在玻璃转化温度（Tg）前后的变化
玻璃转化温度（Tg）因树脂种类而异，如PA66在50℃左右，PA46 的玻璃转化温度接近 80℃。
考虑玻璃转化温度的影响，结晶型材料成型时的模具温度，最好要达到各种材料玻璃化温度之上。这是因为在充分超越 Tg 的模具温度下固化后，分子可在该范围内较为自由地运动，从而大大促进结晶化过程。相反，在偏低温度下，结晶化（即分子的重新配置）将难以进行，从而导致强度等特性降低。一般来说，应避免在玻璃转化温度附近的模具温度下进行树脂材料的成型。
3.1 Thermal state change
Polymer materials is an important physical property value is "glass transition temperature" (also known as the glass transition point). The characteristics of the rational use of the material is important.
Crystalline resins generally have a "glass state", "viscoelastic state (rubber state)" and "molten" and 3 states. As for heating, the resin from the "glass state" into a "viscoelastic state (rubber state)" and "molten." During this period of change points are known as the glass transition temperature (Tg) and melting point (Tm).
Molten easy to understand, but the "glass state" and "viscoelastic state (rubber state)" What is the characteristic? Both are solid, but the different molecular degrees of freedom. In the "glass state", the resin is hard and brittle, and the molecular movement almost impossible; in "viscoelastic state" under, although the crystallization of part of the resin can not exercise, but some can be relatively free of amorphous movement, which has a certain softness (which can be deformed). The ordinary rubber and crystalline resins, since the elastic modulus is different and hence the other soft and hard, but they can be called viscoelastic state. Thus, the physical properties of the glass transition temperature before and after the great changes will occur. This change is usually reflected in the volume, viscosity, strength, hardness and so on. This is the glass transition point is important because.
The physical properties of resin in the glass transition temperature (Tg) before and after the change
Glass transition temperature (Tg) for different type of resin, such as PA66 at 50 ℃, PBT glass transition temperature close to 40 ℃.
Consider the glass transition temperature, crystalline material molding mold temperature, the best materials to achieve above the glass transition temperature. This is because the Tg of the mold in full beyond the curing temperature, the molecules in the relatively free movement within, and thus greatly facilitate the crystallization process. In contrast, low temperature crystallization (ie, molecules re-configuration) will be difficult, leading to lower strength properties. In general, should avoid the vicinity of the glass transition temperature of the mold temperature, molding of resin material.
