Wenjeng Guo

Thermal Properties and Flammability of Ethylene-Vinyl Acetate Copolymer/Montmorillonite/Polyethylene Nanocomposites with Flame Retardants

Ethylene-vinyl acetate copolymer (EVA)/montmorillonite (MMT) composite was blended with a linear low density polyethylene (LLDPE). X-ray diffraction and transmission electron microscopy (TEM) image of the EVA/MMT composite are in support of an intercalated with partially delaminated nanocomposite. The tensile strength of the nanocomposite is about 20% higher than that without layered silicates, MMT. Furthermore, the incorporation of MMT into polymer blend delays the main thermo-oxidative degradation. Cone calorimeter test points out that the addition of layered silicates into the pristine EVA/LLDPE blend or the blend with a low smoke non-halogen (LSNH) fire retardants, aluminum trihydroxide, and antimony trioxide, can reduce the maximum heat release rate by 30–40%. The smoke suppressing effect of layered silicates is only observed in the nanocomposite containing flame retardants. According to the limiting oxygen index (LOI) data and cone calorimeter test, the addition of the nanodispersed layered silicate and LSNH flame retardants to the EVA/LLDPE exhibits a synergistic effect on the flame retardancy and smoke suppression.

Thermoplastic polyurethane/clay nanocomposite foam made by batch foaming

In this study, the foaming of nonwoven fabrics and bulk polymers was investigated. Four different polymers that are commonly used for textiles including polyethylene terephthalate, thermoplastic polyurethane, thermoplastic polyether ester elastomer and polypropylene were foamed by batch foaming. Among the polymers, thermoplastic polyurethane seems to be the most promising material since it possesses the highest cell density and smallest cell size. In addition, nanoclay was added to thermoplastic polyurethane to promote cell nucleation and to increase the cell density. The results showed that well dispersed nanoclay in thermoplastic polyurethane served as an excellent nucleation agent and the cell structure was improved. The cell size of thermoplastic polyurethane nanocomposite foam decreased to 1 µm while the cell density increased to 3 × 1011 cells/cm3.

Kinetic model of hyperbranched polymers formed by the polymerization of AB2 monomer with a substitution effect

Hyperbranched polymers obtained by the polymerization of AB2-type monomer with a substitution effect on the B2 groups were studied by means of the kinetic model. In this polymerization with the substitution effect, if one of the B2 group reacts first, the reactivity of the remaining unreacted B group will be changed. The profiles of the degree of polymerization, polydispersity, degree of branching, and structural units of the hyperbranched polymers with the conversions were all calculated by the generating function method. It is shown that the weight-average degree of polymerization and the degree of branching of the hyperbranched polymers having substitution effect differ from that with equal reactivity of the B2 groups. If the substitution effect causes an increase in the rate constant after one of the B2 groups has reacted, a broader molecular weight distribution and a higher degree of branching are observed.

Preparation of microporous thermoplastic polyurethane by low-temperature supercritical CO2 foaming

Thermoplastic polyurethane possesses many special characteristics. Its flexibility, rigidity, and elasticity can be adjusted by controlling the ratio of soft segments to hard segments. Due to its versatile physical properties, thermoplastic polyurethane is commonly used in transportation, construction, and biomaterials. However, methods for thermoplastic polyurethane foam production using CO2 are still under investigation. We have previously prepared nanoporous thermoplastic polyurethane foam using commercially available thermoplastic polyurethane; however, in this study, thermoplastic polyurethane was synthesized using 4,4′-methylenebis(phenyl isocyanate), poly(propylene glycol) and 1,4-butanediol, without solvents, using a pre-polymer method. The properties of the synthesized thermoplastic polyurethane were characterized by Fourier transform infrared spectroscopy, thermal analysis, and their mechanical properties were measured. The synthesized thermoplastic polyurethane was foamed by batch foaming using supercritical CO2 as the blowing agent. The effect of saturation temperature and saturation time on the cell morphology of the thermoplastic polyurethane foam was examined.

Different approaches for creating nanocellular TPU foams by supercritical CO 2 foaming

In this study, three different approaches were applied to obtain thermoplastic polyurethane (TPU) nanocellular foams. The TPU was synthesized with a 4, 4′-methylenebis (phenyl isocyanate) and 1, 4-butanediol (MDI/BD) hard segment system using a pre-polymer method. The three approaches included increasing the hard segment content, adding a graphene nucleation agent, and replacing the soft segments. Although the synthesized TPUs had a different hardness, it was possible to obtain nanocellular structures with all of the methods. The cell structure is not a function of hardness only. Crystallinity affects the cell structure as well. The addition of graphene and replacement of the soft segments were more effective at yielding nanocellular foams. Our best results showed that after adding 0.1 wt% of graphene, the average cell size of the TPU foam decreased to 715 nm, and the cell density was improved to 4.94 × 1011 cells/cm3. The relative density of the foam could be as low as 0.77. This study first reported elastomer-based nanocellular structures with such low relative density.