测量玻璃化转变温度的考虑

Glass transition temperature, or Tg is an important characteristic of polymeric materials. It marks the point at which a material changes from a glassy to a rubbery state, and influences many other material properties.

Glass transition temperature is characteristic of the type of polymer chain, the amount of crosslinking and chain length or molecular weight. Since most materials have a distribution of molecular weights and cross-linking, the Tg is not a discrete temperature, but rather a temperature range. A single temperature is generally reported for convenience, but the material will actually change properties over a range of temperatures.

由于其与强度和灵活性的密切相关，因此在产品开发生命周期中理解和应用玻璃化转变温度的概念至关重要，以确保聚合物材料，部件和组件在最终使用环境中适当起作用。乐动娱乐官网

是否有理想的玻璃化转变温度（Tg）？

确定理想的玻璃化转变温度取决于材料本身的所需物理性质，以及产品或材料将运行的应用和环境。

当像橡胶和乐动娱乐官网弹性体这样的材料需要保持柔韧性时，应使用并储存在玻璃化转变温度以上（否则，它冒着变脆的风险）。然而，诸如刚性塑料乐动娱乐官网和复合材料的材料应低于玻璃化转变温度。如果在此以上使用，则热量会导致它们具有更低的模量和更高的热膨胀系数。对于复合材料，这导致基于机械树脂的基于机械树脂，例如压缩，剪切和层间张力。对于电子材料，在组装或使用期间乐动娱乐官网，印刷线路可以热应力。这导致镀孔，通孔，引线和焊点的机械应力。为了最佳可靠性，高TG很重要。

外部因素，如湿度或水分，也可能影响玻璃化转变温度。因为水分倾向于通过材料缓慢地扩散，所以它可以用作增塑剂，并使材料基于暴露的相对湿度达到平衡水分含量。这导致较低的玻璃化转变温度。乐动娱乐官网与潮湿环境中的材料相比，在办公环境中使用的材料只能在使用寿命期间拾取适量的水分。因此，低温（远低于固化温度）干燥或受控的湿度暴露可能是合适的。

How is Glass Transition Temperature Testing Performed?

为了确定材料的玻璃化转变温度，可以使用几种不同的测试和报告类型中的一种。使用的方法主要取决于所寻求的结果类型，最终报告中需要哪些数据。

The classical way of measuring glass transition temperature is to perform a series of mechanical tests over the expected temperature range. While there are several options for the test type, flexural strength or shear testing are the standard. Results are reported as a plot of flexural or shear modulus in relation to temperature. The glass transition temperature is indicated where there is a significant drop off in material strength.

由于现代的热分析，近年来，玻璃过渡温度的检测变得明显更快，更便宜。用于确定过渡温度的最标准的热方法是热机械分析（TMA），动态机械分析（DMA）和差示扫描量热法（DSC）。

Tg Testing Methods

热机械分析is (TMA):A thermomechanical analysis uses a small sample of material, which is heated on a quartz stage. A rod inside the machine places a small amount of force on the top of the sample, and the movement of the rod is measured with a linear variable differential transformer or LVDT. The entire instrument is heated at a slow rate, usually 5 degrees C per minute. This data is reported as a curve, where change in length is plotted versus temperature. The slope of the resulting curve is called the coefficient of linear thermal expansion, or COLTE. The glass transition temperature is the point at which the slope of the line changes, as seen below.

TMA may also be used in flexure or penetrations modes. In these approaches a larger force is applied until the probe deflects significantly.

差示扫描量热法（DSC）：In this test method, a small sample is heated while measuring the amount of energy required to heat the sample. This value is then compared to an inert reference material. Because the glass transition temperature will create a change in the properties of the material, the polymer chains reorient, requiring a change in energy to heat. This shows as an inflection on the curve. Three points may be selected and reported: the onset, which is the lowest value, the mid-point and end point.

元素在玻璃化转变温度测量方面的专业知识

As evidenced above, glass transition temperature measurements can vary greatly in technique and calculation based on the specific material type, real world application, and many other factors. Element's polymer scientists have the knowledge and expertise required to support your material testing program and provide you with accurate and applicable data on your material.

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