Structure and physical properties of biaxially stretched polyethylene terephthalate sheet after heat‐setting

Abstract

The consumption of hot‐fillable poly(ethylene terephthalate) bottles is extremely large and is still increasing in Japan. This type of bottle is generally manufactured by the heat‐set method using hot molds after stretch‐blow molding. In this study, the method is simulated using a setting application in which sheets can be stretched constraining their sizes on a hot aluminum block. The crystallinities of the sheets are found to depend on the thermal history, i.e., the duration and temperature of the heat‐set cycle. Heat‐setting mitigates thermal‐shrinkage of the sheets which is due to the increase in crystallinity or in the tense segments in the amorphous region. The structure of the heat‐set sheet varies depending on the original stretched sheet. For a sample of low draw ratio, the crystallinity does not increase because of the heat‐set. For a sample of medium draw ratio, the crystallinity increases greatly and the tense segments in the amorphous region also increase because of heat‐set. For a sample of high draw ratio, the crystallinity increases a little but the numbers of the crystallite and tense segments in the amorphous region do not change with the heat‐set.

Structure and properties of biaxially stretched poly(ethylene terephthalate) sheets

“…The heat-set in Figs. 2 and 3 i s the same as reported previously (2). The heat-set causes the degree of crystallinity and molecular orientation to increase (Fig.…”

“…We will discuss the thermal stability of stretched PET at such temperatures. We have not found any detailed reports discussing the heat shrinkage of PET at such mild temperature except our previous paper (2).…”

“…Thermal shrinkage is given as S=(L,-L)/ lOOL, ( 2 ) where Lo stands for the sample length along the stretch direction before thermal treatment, and L after thermal treatment. During the thermal shrinkage measurement, the sample was allowed to shrink freely in an air circulation oven at 85°C for 1 hour.…”

“…A hotter mold gives a higher thermal stability to the stretched PET according to our previous study (2), in which we only examined the thermal stability of the heat-set sheet that was stretched with a certain stretch condition (draw ratio, stretch speed and stretch temperature). However, high thermal stability is essential irrespective of the variation of the draw ratio from top to bottom for a bottle.…”

Experimental investigation and numerical simulation of liquid supported stretch blow molding

“…One of the key features in these simulations is the PET material characterization. Numerous experimental investigations of representative hot drawing show the strong strain-rate and temperature dependency of PET in terms of stress-strain behavior [14][15][16][17][18][19] and strain induced crystallization [20,21]. Therefore, the preform deformation can be influenced by the temperature profile as well as by the time dependent axial and radial deformation.…”