Measuring Thermal Crystallinity in PET
The mechanical properties of poly (ethylene terephthalate) (PET) depend on the degree of crystallinity. PET crystallizes from both thermal and strain-induced process paths. Strain-induced crystallization occurs under uniaxial or biaxial stretching, the latter is common in stretch blow molding. Thermal crystallization takes place when cooling from the melt or under sustained elevated temperature which are both common during injection and blow molding. The current work focuses on comparing methods used to quantify the percent thermal crystallinity in injection molded water bottle preforms. An injection molded preform with a gradient of induced thermal crystallinity was examined using Differential Scanning Calorimetry (DSC), Micro X-ray Diffraction (μXRD), and Raman Spectroscopy. Correlating these three techniques for percent thermal crystallinity, helps with the development of nondestructive crystallinity measurement methods to aid with process optimization and part quality.
Graphene/poly(ethylene glycol) dispersions for fabrication of nanocomposites: effects of dispersion processing conditions
In the present research, ultrasonic exfoliation was employed to disperse graphene nanoplatelets (GNPs) in poly(ethylene glycol) (PEG) with two molecular weights. The GNP dispersions were added into poly(ethylene terephthalate) (PET) during injection molding to fabricate PET–GNP nanocomposites. The effectiveness of GNPs by weight (ε) in the nanocomposite was evaluated by the improvement in elastic modulus. The ε for the dispersion-dosed nanocomposite at 0.006 wt% was estimated to be 6.65 ± 4 and 20 ± 10 for PEG-600 and PEG-400, respectively. A review of sampled literature on PET nanocomposite elastic modulus improvement indicates that the effectiveness of GNPs obtained by dispersion dosing is significantly greater than other published results. Thus, the early promise of outstanding mechanical reinforcement by graphene in a polymer has been demonstrated.Graphical abstract
Orientation effects on the melting of poly(ethylene terephthalate)
Abstract Poly(ethylene terephthalate) (PET) is used as a loose tube sheathing material for glass optical fibres. It is important that the expansion coefficient of the tubing matches that of the glass fibre and hence the PET tubing is drawn to an amount calculated to give such equality. Extruded tubes of PET with draw ratios up to 5:1 have been examined by differential scanning calorimetry. Orientation progressively increases the temperature of onset of melting, but leaves the degree of crystallinity of the samples unaltered provided they are prepared under identical thermal treatments. Melting occurs over a narrower temperature range, and the height of the maximum specific-heat change during melting is a relative measure of the orientation. Samples with draw ratios above 3.5, which are difficult to distinguish by means of wide-angle X-ray diffraction measurements, can be distinguished by their melting points.