Structure, Morphology And Properties Of Diphenyl-type Polyimide Fibers

As a high performance fiber, polyimide fiber has potential applications in the fields ofmicroelectronics, atomic energy, aerospace, etc. However, it is necessary to study therelationship of structure-property for polyimide fibers deeply. In this thesis, biphenyl-typepolyimide copolymer fibers BPDA/PMDA/ODA, prepared by a two-step method, weresystematically studied, including the spinning process parameters (imidization temperature,heating rate, draw ratio, spray ratio and heat drawing temperature) and comonomer ratio howto influence the structure, morphology and property. The main results are as follows.1. Regarding diphenyl-type polyimide fiber, degree of imidization was characterizedrelatively quantitatively by ATR-IR technique.2. Effects of imidization temperature, heating rate, draw ratio, spray ratio and heatdrawing temperature on fiber morphology, thermal and mechanical property are investigatedsystematically, it is found that:(1) increasing draw ratio, the diameter of fibers decreasesgradually and cross-sectional shape is changed into oval, deviating from round shape. Thechange of spray ratio seems no obvious influence on fiber surface, only makes the interiorcompact. When the heat drawing temperature raises, interior of fibers shows more porosityand even fiber merges appears at460℃.(2) All the fibers exhibit excellent thermal stability.(3) Increasing draw ratio, spray ratio, hot drawing temperature is beneficial to improvementof tensile strength and tensile modulus. But excessive large draw ratio, spray ratio and highheat drawing temperature probably lead to molecular chains broken or degradated. Theoptimum processing conditions are: imidization at280℃with a heating rate of1℃/min, adraw ratio of3.0, a spray ratio of3.25and hot drawing at400℃.3. Increasing PMDA content causes rougher fiber surface and poorer spinnability, butbetter internal compaction. Fiber orientation tends to increase with PMDA. The glasstransition temperature of fibers increases gradually with PMDA and only betweenBPDA/ODA and PMDA/ODA. All the fibers exhibit excellent thermal stability. The tensilestrength, tensile modulus and elongation decrease gradually, indicating that PMDA can notimprove the mechanical properties effectively, which possibly is related to degreeofimidization.