Performance Differences Of PET Plastic Bottles
Sep 12, 2024| Pet resin IV. Value
Under the same conditions, the apparent viscosity of bottle grade PET melt is higher than that of fiber grade PET, and the fluctuation amplitude of apparent viscosity is smaller than that of fiber grade PET. Under the same temperature conditions, the elasticity of bottle grade PET melt is greater than that of fiber grade PET, the degree of structure of the melt is higher than that of fiber grade PET, and the spinnability is poor.
Generally speaking, slices with high viscosity correspond to bottles with higher strength, which can withstand pressure and impact; Slices with low viscosity correspond to lower bottle strength, as well as lower pressure and impact resistance. Due to the high temperature of the melt adhesive during the processing of high viscosity PET slices, the viscosity drop will also increase accordingly. Therefore, the viscosity of bottle grade PET slices is not necessarily better as long as it meets the strength requirements of the product.
The viscosity of PET slices is around 0.70ml/g, which can reach the level of spinning civilian silk. The most important thing is to minimize the fluctuation of intrinsic viscosity. Large fluctuations in viscosity can easily lead to poor molding, drifting, merging, and defects, seriously affecting spinnability. In addition, large fluctuations in viscosity of oil-free fibers can also increase fiber strength fluctuations.
The production process of bottle grade slices and fiber grade slices is basically the same, but in order to meet some of the performance requirements of bottle grade slices, a third monomer, isophthalic acid (IPA), and some additives are added. The addition of the third monomer reduces the melting point of the slices and the crystallization rate of the melt, improves the transparency of the bottles, and the average relative molecular weight of bottle grade PET slices generally exceeds 30000, while fiber grade PET is around 15000-22000.
For every 1% increase in the content of isophthalic acid, the melting point of the slices will decrease by 3-3.5 ℃., The effect of isophthalic acid on the intrinsic quality of slices is mainly to change their crystallization properties. The requirements for the crystallization performance of bottle slices vary among different products, so the content of terephthalic acid cannot be generalized. For example, the weight and wall thickness of edible oil bottle preforms (usually around 110 grams), as well as the slow cooling rate of the preforms, require lower crystallization performance of the bottle slices, which means that the content of isophthalic acid should be as high as possible; Hot filled beverage bottles need to withstand 90 ℃.
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