Property optimization of stretch blow molded PET containers and prediction of container properties from PET film data.
In the two-stage or the reheat-and blow process for the manufacture of PET containers, the preform is heated to the appropriate orientation temperature by infrared heaters before being blown into a bottle. There is a nonuniform temperature distribution through the preform thickness as well as in the axial direction. Since the preform is quite thick (about 150 mils), there is significant difference in the inside and outside hoop stretch ratios. This variation in temperature and hoop ratio through the thickness of the preform causes varying amounts of orientation to be induced through the thickness of the container. In this work, it was proposed to study the effects of nonuniform temperature distributions on the functional properties of blown containers.; The temperature profile through the preform thickness, was computed from process conditions by solving the energy equation with radiation as the heating source. The computed temperature profile was verified by measuring the inside and outside preform surface temperatures using infrared thermocouples. Bottles were then blow molded with different temperature profiles through preform thickness and functional properties were determined. Thickness distributions, axial ratios, mechanical, optical and barrier properties as well as the creep behavior were studied. It was found that the optimum temperature profile depends on the property to be optimized. Mechanical properties are better for bottles blown at a lower blow temperature, while optical clarity, shrinkage, permeability and density are better when the bottles were blown at a higher temperature. Blowing with the inside surface at a higher temperature than the outside surface results in more uniform property variations through thickness and less defects and voids in the sidewall. The creep behavior of containers can be controlled by proper material distribution and higher orientation in the sidewall.; PET films were stretched on the Long Extensional Tester at various temperatures, stretch speeds and stretch ratios. The stretched films were then characterized using various techniques. Prediction of container properties using the data generated for films was undertaken and three different approaches were used. The first method involves the use of time-temperature superposition to extrapolate the film data to the extension rate and extension ratio encountered in bottle blowing. In the second method, correlations developed between functional properties and average orientation functions for films were used for the prediction of properties of blown containers. The third method was a combination of the first two methods. The birefringence was obtained by superposition and other properties were predicted using the correlation between functional properties and birefringence. With the exception of tensile energy absorption, it has been shown that mechanical properties of blown containers can be predicted from film data using any of the three methods previously described. A quantitative measure of property variation through thickness can also be obtained. Using the methods developed in this work, a map of properties and processing conditions encountered in stretch blow molding can be generated and this information can be used for designing preforms and containers.......
【作者单位】: The University of Toledo.
【关 键 词】: Property optimization of stretch blow molded PET containers and prediction of container properties from PET film data.
【授予学位单位】: The University of Toledo.
【学科】: Plastics Technology.; Engineering, Chemical.
【上篇论文】: 学术学位 - Transient and isotopic infrared study of adsorbed species on heterogeneous catalysts.
【下篇论文】: 学术学位 - Rock stability under different fluid flow conditions.