Visualization of polypropylene's strain-induced crystallization under the influence of supercritical CO2 in extrusion

Mechanical Properties of Injection Molded PP/PET-Nanofibril Composites and Foams

The creation and application of PET nanofibrils for PP composite reinforcement were studied. PET nanofibrils were fibrillated within a PP matrix using a spunbond process and then injection molded to test for the end-use properties. The nanofibril reinforcement helped to provide higher tensile and flexural performance in solid (unfoamed) injection molded parts. With foam injection molding, the nanofibrils also helped to improve and refine the microcellular morphology, which led to improved performance. Easily and effectively increasing the strength of a polymeric composite is a goal for many research endeavors. By creating nanoscale fibrils within the matrix itself, effective bonding and dispersion have already been achieved, overcoming the common pitfalls of fiber reinforcement. As blends of PP and PET are drawn in a spunbond system, the PET domains are stretched into nanoscale fibrils. By adapting the spunbonded blends for use in injection molding, both solid and foamed nanocomposites are created. The injection molded nanocomposites achieved increased in both tensile and flexural strength. The solid and foamed tensile strength increased by 50 and 100%, respectively. In addition, both the solid and foamed flexural strength increased by 100%. These increases in strength are attributed to effective PET nanofibril reinforcement.

The crystallization morphology and process of stereocomplex crystallites of polylactide under CO2: the effect of H-bonding and chain diffusion

The crystallization of PLA SC under CO2 was in situ investigated for the first time.

Enhancing the accuracy and efficiency of characterizing polymeric cellular structures using 3D-based computed tomography

Characterizing the morphology of polymeric foams is crucial for determining their practical applicability. The internal cellular structure of polymeric foams is typically analyzed by 2 D imaging techniques, such as Scanning Electron Microscopy (SEM) and optical microscopy. The problem with these techniques is that their tests are tedious, destructive, and the accuracy of the obtained results is questionable. The objective of this paper is to establish and experimentally verify an efficient 3- dimensional (3 D) Microcomputed-tomography based methodology for reliably estimating and characterizing each of the phases commonly present in multiple types of polymeric foam samples, such as the open, the closed, and the solid phase. A comparative study was carried out between morphology data obtained from 2-dimensional (2 D) analysis and those obtained from 3 D analysis to investigate the reliability of the 2 D analysis results. In this context, the experimental results revealed that by using a 2 D method the open porosity was underestimated at the expense of closed porosity, which in turn was overestimated, while the total porosity was not impacted. Also, visualization of the internal structure of polymer foams by using Micro-CT provides details about the 3 D space which cannot be obtained from SEM images. The analysis of foamed specimen demonstrated that the polymeric foam phases extracted from Micro-CT images were in agreement with the experimentally measured values of total porosity of the samples. In an effort to reduce computational requirements, the effects of reducing data size on the accuracy of results has also been studied by averaging image pixels in 3 D space and the results were compared for multiple types of foam structures. This method reduced the processing time considerably, and yielded comparable porosity values. However, the number of detected pores were lowered due to the inability of this method to detect very small cells after 3 D averaging of image pixels.

Ultralight Microcellular Polymer-Graphene Nanoplatelet Foams with Enhanced Dielectric Performance

Dielectric polymer nanocomposites with high dielectric constant (ε') and low dielectric loss (tan δ) are extremely desirable in the electronics industry. Percolative polymer-graphene nanoplatelet (GnP) composites have shown great promise as dielectric materials for high-performance capacitors. Herein, an industrially-viable technique for manufacturing a new class of ultralight polymer composite foams using commercial GnPs with excellent dielectric performance is presented. Using this method, the high-density polyethylene (HDPE)-GnPs composites with a microcellular structure were fabricated by melt-mixing. This was followed by supercritical fluid (SCF) treatment and physical foaming in an extrusion process, which added an extra layer of design flexibility. The SCF treatment effectively in situ exfoliated the GnPs in the polymer matrix. Moreover, the generation of a microcellular structure produced numerous parallel-plate nanocapacitors consisting of GnP pairs as electrodes with insulating polymer as nanodielectrics. This significantly increased the real permittivity and decreased the dielectric loss. The ultralight extruded HDPE-1.08 vol % GnP composite foams, with a 0.15 g·cm^-3 density, had an excellent combination of dielectric properties (ε' = 77.5, tan δ = 0.003 at 1 × 10⁵ Hz), which were superior to their compression-molded counterparts (ε' = 19.9, tan δ = 0.15 and density of = 1.2 g·cm^-3) and to those reported in the literature. This dramatic improvement resulted from in situ GnP's exfoliation and dispersion, as well as a unique GnP parallel-plate arrangement around the cells. Thus, this facile method provides a scalable method to produce ultralight dielectric polymer nanocomposites, with a microscopically tailored microstructure for use in electronic devices.