Antinucleating action of polystyrene on the isothermal cold crystallization of poly(ethylene terephthalate)

Effect of 3D Printing Temperature Profile on Polymer Materials Behavior

This article presents the effect analysis of the printing time sequences on the mechanical properties in correlation with the crystallization kinetics and rheological behavior. For this purpose, two printing order of 3D printed samples (printed simultaneously or in sequence) were chosen. In addition, two different infill patterns (line and gyroid) and building directions (horizontal and vertical) have been used. Concerning the polymer filaments, two commercial polylactic acid (PLA 3D870 and PLA 3D850) having different crystallization kinetics were used. The effect of the printing time delay between each layer on the temperature profile and the crystallization evolution was studied using a finite element analysis method simulation. The simulation results show a greater thermal excursion for longer delay times between the layers and with a crystallization degree evolution characterized by a step pattern. Moreover, a major density of crystals appears in the center of the final part. A new approach was adapted to measure the volumetric contraction of the material as a function of the temperature; it was performed with a gap test using a rotational rheometer under static conditions (without external deformation). The normal force measured from the test has shown a faster and higher increase of the contraction for the material with faster crystallization kinetics and with a higher degree of crystallinity. The results concerning the tensile properties show better rigidity for the samples printed in sequence due to the minor time of delay between the deposited layers. The mesostructure of the printed parts was analyzed with an X-ray tomography and a scanning electron microscope. The highest difference is presented from the PLA 3D870 characterized by the highest rate of crystallization resulting in more microvoids compared with the PLA 3D850, due to the less welding cohesion between the layers.

Composite Fibers from Recycled Plastics Using Melt Centrifugal Spinning

New methods are being developed to enable the production of value-added materials from high-volume, low-cost feedstocks arising from domestic recycling streams. In this work, recycled bottle-grade polyethylene terephthalate, polystyrene, and polypropylene were spun into fibers from the melt using a centrifugal spinning technique. Mono-component fibers and 50/50 blends of each polymer and a 33/33/33 blend of all three polymers were evaluated. Fiber morphology, chemistry, thermal, and mechanical properties were probed. Fiber diameters ranged from ca. 1 to over 12 µm, with polypropylene fibers having the smallest fiber diameters. Mono-component fibers were generally defect-free, while composite fibers containing polypropylene were beady. Fibers made from polyethylene terephthalate had the highest tensile strength, and the addition of polyethylene terephthalate to the other polymers improved the mechanical properties of the blends. Nano- and micro-fibers from both pure and mixed waste streams are expected to have applications in myriad areas such as ultra/micro-filtration, composites, and insulation.

Efeito da adição de PHB na cristalização a frio do PET

O presente trabalho investigou o efeito da adição de baixas concentrações (0,5 e 1,0%) de poli(3-hidroxibutirato) (PHB) na cristalização isotérmica a frio do poli(tereftalato de etileno) (PET). As curvas de energia foram obtidas por calorimetria exploratória diferencial (DSC) e a cinética de cristalização foi analisada pelo método de Avrami. Dois estágios de cristalização foram observados. Os resultados mostraram que o PHB promove alterações na taxa de cristalização do PET, como verificado por mudanças nos tempos para se atingir 1, 10, 30, 50 e 99% de cristalinidade relativa. As energias de ativação para o primeiro e segundo estágios da cristalização foram determinadas através das curvas de Arrhenius, sendo praticamente independentes da presença de PHB nas misturas PET/PHB. As temperaturas de fusão de equilíbrio foram determinadas de acordo com o procedimento de Hoffman e Weeks; as misturas PET/PHB apresentaram valores mais elevados deste parâmetro sugerindo que o PHB altera a estrutura cristalina do PET.