Grade Polyethylene Terephthalate Research Articles

Melt processing behaviour and structure development in recycled PP blends with recycled PET

Commercially available recycled polypropylene (R-PP) and recycled bottle grade polyethylene terephthalate (R-PET) were melt compounded in different proportions of R-PET in twin screw extruder at temperatures used typically for PP processing. The melt flow behaviour was investigated for these blends using capillary rheometer at different temperatures viz. 230, 250, 260°C. The crystallization and structure development was studied using DSC and XRD. The melt viscosity (η) of these blends followed the usual non-Newtonian behaviour with decrease of η with high shear rate (γ′) and saturation at low shear rate. Most noteworthy finding was that the low shear viscosity at melt temperatures of 230 and 250 showed a peak with increase of R-PET content while at 260°C there was uniform decrease in the viscosity with addition of R-PET. The high shear viscosity also showed similar trend but with less pronounced changes. This was attributed to the cross over of domain shape from spherical to ellipsoidal and finally fibrous shape according to Utracki model. At the melt compounding/processing temperature of 230°C, the R-PET phase was in semi solid state and hence it formed fibrous morphology in the PP melt which was confirmed by SEM analysis. The most interesting finding was that crystallization of both the component polymers was affected due to the presence of the other. R-PP showed nucleation effect in presence of R-PET with the shift in Tc from 118°C to higher temperature side (123°C). Even R-PET exhibited shift in the Tc from 178°C to 201°C in presence of R-PP. These results are discussed in terms of nucleation and slow heat dissipation for PET domain in PP melt together with shear induced crystallization. These structural modifications in the R-PP/R-PET blends led to improvement in properties at certain compositions processed under certain conditions.

Rheological/thermal properties of poly(ethylene terephthalate) modified by chain extenders of pyromellitic dianhydride and pentaerythritol

AbstractDue to low molecular weight and wide molecular weight distribution, polyethylene terephthalate (PET) shows weak melt strength properties. In this study, the synergistic effect of using different types of chain extenders and catalyst on rheological behavior of PET has been investigated. Long‐chain branching is known as a suitable method for developing the structure of PET during reactive melt processing. Thus, pyromellitic dianhydride (PMDA) and pentaerythritol (PENTA) were added to the fiber grade PET. The best formulation was determined based on rheological results, which revealed an improvement in both storage modulus and complex viscosity of PMDA‐modified samples. Samples containing 1.5% PMDA and 0.5% PENTA exhibited the best rheological properties. Also, dibutyltin dilaurate (DBTDL) acted as an accelerator for chain extension reaction during reactive melt blending. Subsequently, the rheological properties were improved by increasing the chain extending rate. Moreover, thermal properties such as crystallization and melting temperatures and the degree of crystallinity for modified PET were investigated by differential scanning calorimetry.

Experimental study on texturability of filament yarns produced from recycled PET

In the present work, the texturability of filament yarns produced from recycled bottle grade polyethylene terephthalate (R-PET) and new fiber grade PET (FG-PET) were investigated and compared experimentally. Yarn spun on a spin-draw spinning machine was draw-textured. Elongation at break in each fiber was set to reach 30 ± 5% in the texturing machine. The effect of the draw-texturing conditions on thermomechanical, structural, and crimp properties were examined. Draw-texturing behaviors of the fibers were analyzed using differential scanning calorimetry and measurements of intrinsic viscosity, mechanical and crimp properties, density, and X-ray diffraction. The results indicate that crystallinity of the textured yarn from R- PET and FG-PET has increased compared to the semi-drawn yarns. Further, the lateral dimensions of the R-PET crystals are relatively well developed. Crimp properties show nearly similar response for two polymer yarns for the texturing process. It was found that R-PET can be the premier feed supply for the draw-texturing process and that filaments with appropriate confidence could be obtained from the R-PET.

Effects of electron beam sterilization on polyethylene terephthalate: Physico-chemical modifications and formation of non-volatile organic extractables

Our investigations hereby involve the effects of ionizing radiation as a sterilization method, and especially electron beams, on a medical grade Polyethylene Terephthalate (PET). Ionizing radiations are known to induce free radicals formation in the polymer that will then either degrade or crosslink, depending on its chemical nature, ionizing type and irradiation atmosphere (Charlesby, 1967; Dole, 1972 and Dole, 1973). The evaluation of packaging material modifications under radiation sterilization is of great interest and the objective of our paper is to focus on both PET volume modifications and extractable analyses after electron beam sterilization. As regards the polymeric matrix and after sterilization, we did not observe by means of spectral analyses, any single chemical modification whatsoever, whereas by thermal techniques we evidenced polymer chain scissions. As for the non-volatile organic extractables, we further substantiate the presence of numerous compounds, namely oligomers and trimers especially, along with benzoic and terephthalic acids in particular. With respect to pharmaceutical stakes however, we claim herein that the 25kGy sterilization dose used, triggers oligomers and extractables formation, a result which is promising for further risk analysis.

Dye Uptake and Thermal Behavior of Fibre Grade PET Containing Boltorn H40 as a Nanomaterial

In this work, various loads of nanomaterials and aliphatic dendritic polymerswere mixed with flbre grade PET (Polyethylene terephthalate) to study its dye ability, thermal and thermal-mechanical properties. A twin screw extruder equipped with sheet (proflle) die was used for mixing the compounds. Thermal behaviour of the neat PET and the compounded sheet samples were studied using difierential scanning calorimeter and dynamic mechanical thermal analysis. It was observed that the Tg of samples decreased gradually by increasing the load of Boltorn H40 as a nanomaterial additive while the Tm remained almost the same. The difierence between the glass transition temperature for neat PET and the compounded sample including 3% additive was about seven degrees. In spite of the decline in Tg, the moduli of samples containing additive increased as revealed by DMTA analysis. The presence of this dendritic polymer in compounded PET acted as a cross linking or antiplastisizing agent and made the flbre grade PET compounds more compact than pure PET. So the disperse dye molecules neither were able to stay between the molecules of compounded PET nor were able to trap between the dendritic branches.

Compounding fibre grade polyethylene terephthalate with a hyperbranched additive and studying its dyeability with a disperse dye

A hyperbranched polymer which comprised a polyesteramide structure was used to study improvements in dyeability of fibre grade polyethylene terephthalate films. The optical measurements of the dyed samples showed that, by increasing the percentages of the dendritic additive, K/S as a dye uptake parameter changed in the presence or absence of a carrier. The amount of chroma increased while the hue did not change significantly. The dyeability of the prepared samples was attributed to the decrease in glass transition temperature and the lower crystallinity of the polymer, as studied by differential scanning calorimetry. Thus, a new fibre grade polyethylene terephthalate, which is dyeable, could be obtained, with less need to use a toxic carrier compound.

Blends of a bottle grade polyethylene terephthalate copolymer and a liquid crystalline polymer. Part I: Injection molding morphology and rheological properties

AbstractBlends of a bottle grade polyethylene terephthalate copolymer (PET) with a liquid crystalline polymer (LCP) were prepared by injection molding. The thermal transitions, the morphology and the rheological properties of the pure components and of the blends were measured by dynamic mechanical analysis (DMTA), scanning electron microscopy (SEM) and capillary and parallel plates rheometry, respectively. The blends displayed only one Tg; the B60 and B80 compositions showed the highest LCP β‐transition, which has been correlated to good barrier properties. In all the blends a “skin‐core” type morphology was observed; the core region had two phases while the skin region showed only one fibrillar phase. The viscosity measurements gave an indication that the interface was strong, probably due to transterifications reactions that occurred during the tests. On creep recovery, the increasing addition of the LCP to the PET increased the blends elastic recovery. On stress growth, the highest stress overshoot was displayed by the pure LCP; this polymer actually presented two overshoots that were also observed in some of the blends at high shear rates.

Structure and rheology of recycled PET modified by reactive extrusion

In this work pyromellitic dianhydride (PMDA) was used as a chain extender to increase the molecular weight of polyethylene-terephthalate (PET) industrial scraps with low intrinsic viscosity ( IV=0.48 dl/g), coming from a PET processing plant. The reaction was performed in a single step through reactive extrusion. Different percentages of chain extender were used in order to investigate the effect of PMDA content on the molecular structure (average molecular weight, molecular weight distribution, branching) of PET. Rheological and thermal characterizations were performed on treated PET extruded samples. In particular, the increase in the dynamic viscosity at low frequencies and the high pronounced shear thinning behavior observed in the PMDA-treated PET samples were correlated to the broadening of the M w/ M n and to the long chain branching. These structural changes are also responsible for the decrease in the T mc and Δ H mc and the increase in the T cc values increasing the PMDA content in the PET samples. The study was performed also on bottle grade PET ( IV=0.74 dl/g) for comparison purpose. The results have pointed out that with an amount of PMDA included between 0.50 and 0.75% the chain extending reaction produces an increase of M w, a broadening of M w/ M n and branching phenomena, that modify the PET scraps in order to make the recycled polymer suitable for film blowing and blow molding processes.