Although the performance of PTFE material is stable, its shortcomings are also obvious.

(1) Polytetrafluoroethylene has "cold flow". That is, the plastic deformation (creep) of material products under long-term continuous load, which brings certain restrictions to its application. For example, when PTFE is used as a gasket, the bolts are tightened very tightly for a tight seal, so that when a specific compression stress is exceeded, the gasket will produce "cold flow" (creep) and be crushed. These shortcomings can be overcome by adding appropriate fillers and improving the structure of parts.

(2) Polytetrafluoroethylene has a high melt viscosity and does not flow at high temperatures. It is above the melting point (327℃), and the melt viscosity reaches 1 010Pa.s. It does not flow even if heated to the decomposition temperature, which makes it impossible to use general thermoplastic molding methods, but to use sintering methods similar to powder metallurgy. forming.

(3) PTFE has outstanding non-stick properties, which limits its industrial application. It is an excellent anti-sticking material, and this performance makes it extremely difficult to bond with the surface of other objects.

(4) PTFE has low thermal conductivity and poor thermal conductivity, which not only prevents it from being used as a bearing material, but also prevents quenching when manufacturing thick-walled products.

(5) The linear expansion coefficient of PTFE is 10-20 times that of steel, which is larger than most plastics, and its linear expansion coefficient changes very irregularly with temperature changes. In the application of PTFE, if insufficient attention is paid to this aspect, it is easy to cause losses.

(6) When heated above 400°C, the cracking speed of PTFE gradually increases, and the decomposition products are mainly tetrafluoroethylene, perfluoropropylene and octafluorocyclobutane. Above 475°C, the decomposition product has a very small amount of highly toxic perfluoroisobutene. Note that the heating temperature should not exceed 400°C, and the laboratory should have a good ventilation system to help eliminate toxic gases.

聚四氟乙烯的缺点

尽管聚四氟乙烯材料性能稳定，但其缺点也很明显。

(1)聚四氟乙烯具有“冷流性”。即材料制品在长时间连续载荷作用下发生的塑性变形(蠕变)，这给它的应用带来一定的限制。如当PTFE用作密封垫时，为密封严密而把螺栓拧得很紧，以致超过特定的压缩应力时，会使垫圈产生“冷流”(蠕变)而被压扁。这些缺点可通过加入适当的填料及改进零件结构等方法来克服。

(2)聚四氟乙烯的熔体粘度很高，在高温下也不流动。它在熔点(327℃)以上，熔体粘度达到1 010Pa.s，即使加热到分解温度也不流动，这就使它不能采用一般热塑性塑料的成型方法，而要采用类似粉末冶金那样的烧结方法成型。

(3)PTFE具有突出的不粘性，限制了其工业上的应用。它是极好的防粘材料，这种性能又使它与其他物件的表面粘合极为困难。

(4)PTFE的导热系数低，导热性能较差，这不仅妨碍它用作轴承材料，而且使得制造厚壁制品时不能淬火。

(5)PTFE的线膨胀系数为钢的10~20倍，比多数塑料大，其线膨胀系数随着温度的变化而发生很不规律的变化。在应用PTFE时，如果对这方面性能注意不够，很容易造成损失。

(6)在400℃以上加热时，聚四氟乙烯的裂解速度逐渐加快，分解产物主要是四氟乙烯、全氟丙烯和八氟环丁烷。在475℃以上，分解产物有极少量剧毒的全氟异丁烯。注意加热温度不能超过400℃，且实验室要有良好的通风系统，利于排除毒性气体。