Morphological Study and Dielectric Behavior of Nonisothermally Crystallized Poly(ethylene naphthalate) Nanocomposites as a Function of Graphene Content

Morphological evolution and dielectric properties of poly(ethylene naphthalate)- (PEN-) graphene nanocomposites nonisothermally crystallized have been investigated. PEN-graphene nanocomposites containing 0.01, 0.025, 0.05, 0.075, and 0.1 wt% of graphene were prepared by melt blending in a mini twin screw extruder. The results showed that graphene exhibited a superior influence on morphological and conformational structure of PEN during nonisothermal crystallization at low graphene contents. Crystallization temperature (Tc) was found to be increased up to 18°C supporting the high nucleating activity of graphene layers. Wide angle X-ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR) indicated that graphene modifies the conformation of PEN chains promoting crystallinity and favoring the evolution from α to β crystalline form with homogeneous lamellar thickness. It may be attributed to the structural similarity between naphthalene rings and graphene structure and to π-π interactions during nucleation. Dielectric behavior was found to be a function of graphene content where the nanocomposites changed from dielectric to low conducting material when passing from 0.075 to 0.1 wt% of graphene content. This phenomenon permits having a wide range of properties to fit a wide variety of applications required to store electrical energy of low voltage

Effect of Different Nucleating Agents on the Crystallization of Ziegler-Natta Isotactic Polypropylene

Ziegler-Natta isotactic polypropylene (iPP) was melt mixed with four different nucleating agents (carbon nanotubes (CNT), carbon nanofibers (CNF), lithium benzoate (LiBe), and a sorbitol derivative (Millad)) in order to study their effect on the crystallization of iPP. It was found that the four different nucleating agents promote the alpha crystalline form. At 0.01 wt%, the carbon nanoparticles produced the higher crystallization temperature “Tc” (~119°C), whereas, at 0.10 wt%, LiBe and Millad produced a markedly higher Tc (~125°C). Tc of pure iPP was 111°C. With 0.1 wt% nucleating agent, at 120°C, the crystallization half-life time of PP, when using LiBe or Millad, was 15 times faster than for pure PP, whereas, when using carbon nanoparticles, it was 20–25 times faster. At 135°C, with 0.01 wt% nucleating agent, the isothermal crystallization process of iPP was completed after 25 min, as well as with Millad. With LiBe, it was completed after just 15 min and, with any of the carbon nanoparticles, it was practically over after only a couple of minutes

Co-Plasticization of Starch with Glycerol and Isosorbide: Effect on Retrogradation in Thermo-Plastic Cassava Starch Films

Thermoplastic starch (TPS) has emerged as an essential alternative to produce environmentally friendly packaging; however, retrogradation is a disadvantage that affects its shelf life. This study analyzed the co-plasticizing effect of isosorbide on the mechanical, thermal, physicochemical, and microstructural properties and the retrogradation of films obtained by blown film extrusion from thermoplasticized starch with mixtures of glycerol and isosorbide in different ratios (3:0, 2:1, 1:2, and 0:3, respectively). The results showed that the higher concentration of isosorbide significantly increased the tensile strength; however, it reduced the elongation. Retrogradation modeled using the Avrami equation showed that the presence of isosorbide reduced the retrogradation rate (k) and modified the recrystallization mechanism (n). The relative crystallinity in the plasticized TPS films was reduced to 89%, and the adsorption significantly decreased. Isosorbide was very important in reducing the retrogradation of TPS. The best performance was obtained with the 2:1 ratio of glycerol/isosorbide due to the synergistic effect between the plasticizers. The results would allow tuning the properties of TPS films by combining glycerol/isosorbide in different ratios, which enables the design of materials tailored to potential application requirements