Study On Structure And Properties Of PET Filaments

Polyester fiber products were first introduced by Du Pont Co. in 1953.England Imperial Chemical Industries (I.C.I) built up both staple andfilament plants in 1955. The annual output of filament was approximate1000 tons. In contrast, the output of PET Filament in China grew rapidly in1990s. The ratio of filament to staple has increased from 14.1:85.9 in1985 to 51.2.. 48.8 in 1994. The yield of filament overtaking staple reachedto 5.74 million tons in 2003.To cater for the market competition, a great variety of filament productsare made with less evaluation time, more stable manufacturing and higherproduct quality. Therefore, it is indispensable to conduct fundamentalresearch work on the structure and properties as well as the effect ofmanufacturing process on comprehensive properties. This project is basedon the current production situation of our company in combination withoperating process conditions.The influence of the microstructure and property for POY filaments onpost process was compared. The properties of PET POY were dependent onits microstructure. The break elongation, boiling water shrinkage andcharacteristic structure parameter (ε_0.2) decrease with the rising crystallinityof fibers; property variation coefficients increase with the degree of non-uniformity in microstructure. Sample #2 demonstrates the excellent postprocess properties due to its even molecular distribution, slow crystallizationrate, and low uniform microstructure.The impact of DTY post process conditions on structure and properties offibers was also characterized. A certain degree of crystalline orientation offilament formed in the first hot box due to tensile stress, twisting canprevent the crystallization and orientation of the filament in the first heating chamber, which leads to lower crystallinity and orientation factor of highelastic filaments than drawing filaments. The crystallinity and lattice size ofas-formed filaments after heat treatment in the second heating chamberappropriately increase, however their orientation factor decrease resulting inthe reduction of shrinkage.The effect of process parameters such as 1st heating chamber, drawingratio, process rate, D/Y ratio, 2nd heating chamber and super feed ratio onstructure and properties of low elastic filaments was emphasized. Theoperating parameters in friction in-draw texturing machine affect themechanical, crimp and dying properties of fibers. Therefore, the high-performance fibers can be made by control of all the parameters. The riseof temperatures in the 1st heating chamber within the range of processparameters results in increase in crystallinity and decrease in orientation oflow elastic filaments. The structural change of low elastic filaments leads todecease of break elongation, sharp drop in fracture strength attemperatures beyond 215℃and lowest dying saturation value at 205℃.With the rise of 2nd heating chamber, the crystallinity of low elasticfilaments became stable at temperatures above 160℃and reached themaximum orientation at 180 with decrease of both crimp stability and crimpcontraction The increase of process speed results in decreasing crystallinityand break strength. The variation factor of break elongation increasegreatly when the process speed is beyond 650m/min. The crystallinity oflow elastic filaments does not change significantly at 2.2％of feed rate, butorientation decrease with the increase of setting super-feeding, whichresults in decrease of onset modulus and crimp stability and increase ofdying saturation. The crystallinity, f_s an f_a, break elongation and strengthdrop sharply at 1.95 of stretch ratio. There is a little effect of D/Y ratio onstructure and properties of low elastic filaments. However, the breakelongation variation factor will be larger at either low D/Y or high D/Y. The effect of spin speed and cross air blow rate on structure andproperties of FDY was also investigated. The crystallinity andmacromolecular orientation decrease with the increase of spin speed, thusresulting in decreased boiling water shrinkage and strength. The change ofside blow rate does not impact the structure and property of final FDYproducts but greatly affect filament unevenness. The appropriate increaseof spin speed and reasonable side air rate can be used to reduce filamentunevenness of FDY.This study provides useful information on how to optimize the processparameters of PET filament and technical support for high qualityproduction as well as the experience accumulation for future new productdevelopment.