Insights into crystallization and melting of high density polyethylene/graphene nanocomposites studied by fast scanning calorimetry

Abstract

Vourlias, G. (2018). Insights into crystallization and melting of high density polyethylene/graphene nanocomposites studied by fast scanning calorimetry. Polymer Testing, 67,[349][350][351][352][353][354][355][356][357][358] AbstractGraphene nanoplatelets (5 wt.%) with different diameters (5 and 25 x 10 -6 m in diameter, 6 x 10 -9 m in thickness) filled high density polyethylene nanocomposites were prepared by the melt-mixing method and the effect of graphene nanoplatelets on the polymeric matrix are then investigated by X-ray diffraction, polarized light microscopy, differential scanning calorimetry, fast scanning calorimetry, and rheology. Polarized light microscopy revealed that graphene nanoplatelets of 5 x 10 -6 m promote the decrease in the size of the spherical aggregates during crystallization compared to larger nanoplatelets. From rheological measurements, it was found that even though the viscosity of the nanocomposites with increasing filler diameter was increased significantly compared to the neat polymer, the processability of these 2 materials was not affected. Several melting events for neat high-density polyethylene and graphene nanocomposites were observed by fast scanning calorimetry associated with the small imperfect crystals grown at large supercooling, the nucleation efficiency and the diameter size of the filler. The activation energy values versus the relative extent of crystallization revealed that graphene nanoplatelets block the movement of the molecular segments and make crystallization difficult, especially at the final stage of the process. Based on this work, it can be concluded that the nanocomposite with the smaller diameter showed the most enhanced crystallization kinetics as graphene increased the number of nucleation sites, while the larger ones hindered the melted molecules in reaching full isotropization above the melting temperature. determined by conventional DSC (filled symbols) and FSC (open symbols)

Electrically and Thermally Conductive Low Density Polyethylene-Based Nanocomposites Reinforced by MWCNT or Hybrid MWCNT/Graphene Nanoplatelets with Improved Thermo-Oxidative Stability

“…This gave a significant reduction of melting temperature up to 3.8%. Moreover, Tarani et al [ 61 ] indicated that the addition of GNPs in HDPE decelerated the overall crystallization process of matrix. GNPs behave as a barrier during the mass transfer forming a tortuosity in the diffusion path, which decreases the free volume and retard the crystalline-amorphous interface movement [ 62 , 63 ].…”

Influence of Graphene Platelet Aspect Ratio on the Mechanical Properties of HDPE Nanocomposites: Microscopic Observation and Micromechanical Modeling

“…In our previous works on HDPE/GNP nanocomposites [ 33 , 34 , 35 ], it was found that GNP M25 with the larger diameter size reduced the chain mobility in the semi-crystal HDPE matrix causing the degradation of the HDPE to be retarded. The large contact areas and continuous paths increased the thermal conductivity values.…”

Nonisothermal crystallization kinetic studies on melt processed poly(ethylene terephthalate)/polylactic acid blends containing graphene oxide and exfoliated graphite nanoplatelets

“…Moreover, Cazé and Chuah average Avrami models were also failed as neither took into account secondary crystallization process of the system . Using a fast scanning calorimetry method, Tarai and coworkers observed several melting events, associated with the small imperfect crystals grown at a large supercooling, for neat high‐density polyethylene (HDPE) and its nanocomposites containing graphene …”