Xingrong Zeng

Synthesis and Characterization of UV-curable Hyperbranched Urethane Acrylate

The UV-curable hyperbranched urethane acrylate (HBUA) with a multi-hydroxyl functional hyperbranched polyester core was synthesized via a two-step procedure. The products were characterized by size exclusion chromatography, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and thermogravimetric analysis. The mechanical properties of UV-cured HBUA films were also investigated. The polydispersity index of HBUA is 2.31 and the endcapped degree of acrylation is 79.8%. The viscosity of HBUA is relatively low in favor of mixing and spreading. The UV-cured films exhibit high hardness and good flexibility.

Preparation and Characterization of Conductive Polypyrrole/Organophilic Montorillonite Nanocomposite

Polyvinylpyrrolidone (PVP) was used as organic intercalative modifier to prepare organophilic montorillonite OMMT-P. PPy/OMMT nanocomposites were prepared by the oxidative polymerization of pyrrole (Py) intercalated into the interlayer of OMMT. The effect of Py, OMMT, oxidant, and dopant content on nanocomposites conductivity were studied, and the conductivity of PPy/OMMT-P was achieved as high as 15.0 S·cm−1 when the molar ratio of FeCl3 and Py is 2.50, the mass ratio of Py and OMMT-P is 0.25, and the TSANa concentration is 0.025 g·ml−1. The structure and properties of the nanocomposites are characterized with FT-IR, TG, and XRD.

Synergistic Effect of Epoxy/Organophilic Montorillonite Nanocomposites and Triphenyl Phosphate on Flame Retardance Enhancement of Polypropylene

Epoxy/organophilic montorillonite (Epoxy/OMMT) nanocomposites were prepared by epoxy intercalated into the interlayer of OMMT, and flame retardant polypropylene (PP) was obtained with Epoxy/OMMT nanocomposites and triphenyl phosphate (TPP) mixture as flame retardant agent. The effect of epoxy sorts, mass ratio of OMMT and Epoxy, and the contents of Epoxy/OMMT and TPP on properties of PP were studied. It was found that there is a remarkable synergistic flame retardant effect of novolac epoxy/organophilic montorillonite (NE/OMMT) and TPP on PP. Flame retardant PP with oxygen index (OI) value of 36.5%, peak heat release rate (PHRR) of 654 kW/m2, notched Izod impact strength of 6.93 kJ/m2 and tensile strength of 30.56 MPa was obtained when the mass ratio of OMMT and NE is 5:100, the content of NE/OMMT and TPP is 13.33 and 6.67 wt.%, respectively. The materials were characterized via X-Ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectrum (FT-IR), and thermogravimetry (TG). The XRD results and TEM photograph indicate OMMT is exfoliated in PP matrix when the mass ratio of OMMT and NE is lower than 10:100. The TG results show the evaporation of TPP is greatly hampered by NE/OMMT nanocomposite. PP with NE/OMMT-TPP has an onset weight loss temperature 31.7°C higher than PP with NE-TPP because of the shielding effect of OMMT layers. The FT-IR spectra indicate phosphoric acid is generated from TPP and carboxylic acid and phenyl ether are generated from NE under thermal degradation, which further results in the formation of thermally stable char. This charring process is also affirmed by the wide thermally stable zone at 380–550°C in TG curves of PP with NE/OMMT-TPP or NE-TPP.

Synthesis and Thermo-Oxidative Aging Resistance of Hydroxyl Terminated Polybutadiene Bound 2,2-Thiobis(4-methyl-6-tert-butylphenol)

A novel polymeric antioxidant HTPB-IPDI-TPH was synthesized by the reaction between 2,2-thiobis (4-methyl-6-tert-butylphenol) (TPH) and an adduct (HTPB-IPDI) from hydroxyl terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI). The effects of raw materials ratio and the reaction condition were investigated by measuring the content of the residual –NCO groups of the reactants during the reaction. The structure of HTPB-IPDI-TPH was characterized by FTIR and 1H NMR. Thermo-oxidative aging resistance of HTPB-IPDI-TPH was evaluated by oxidation induction time (OIT) from DSC of natural rubber vulcanizates. The optimal reaction conditions between IPDI and HTPB were that the amount of dibutyltin dilaurate (DBTDL) was 0.6 wt% based on IPDI, and the temperature and time were 40°C and 270 min, respectively. The reaction conditions between TPH and HTPB-IPDI were that the molar ratio of TPH to –NCO in HTPB-IPDI was 3:1, and the amount of DBTDL was 1.6 wt% based on the total of reactants, and the temperature and time were 75°C and 360 min, respectively. Thermo-oxidative aging resistance of HTPB-IPDI-TPH was obviously superior to the corresponding low molecular counterpart (TPH) for natural rubber vulcanizates.

Epoxidation of Styrene-Isoprene-Styrene Block Copolymer and Its Use for Hot-Melt Pressure Sensitive Adhesives

The epoxidation of styrene-isoprene-styrene block copolymer (SIS) with performic acid generated in situ from hydrogen peroxide and formic acid was studied, and the hot-melt pressure sensitive adhesives (HMPSA) were prepared with epoxidized SIS (ESIS), SIS and the tackifier ESCOREZ-2203LC. The 1H nucleal magnetic resonance and Fourier transform infrared spectra revealed that the epoxidation reaction mainly occurred in 1,4-isoprene units of SIS, and the reactivity of the cis-1,4-structure was higher than that of the trans-1,4-structure. Analysis by Gel Permeation Chromatography (GPC) showed that the molecular weight of SIS increased and the molecular weight distribution widened after epoxidation. Differential scanning calorimetry analysis showed that ESIS was compatible with SIS and ESCOREZ-2203LC. The addition of certain amount of polar ESIS in the HMPSA was beneficial to the improvement of 180° peel strength when the substrates were polar materials, such as PVC and steel. With the increase in peeling rate, the peel failure mode changed to adhesion failure from cohesion failure.

Effect of curatives and fillers on vulcanization, mechanical, heat aging, and dynamic properties of silicone rubber and fluororubber blends:

The cure characteristics and mechanical properties of gum and filled silicone rubber (MVQ), fluororubber (FKM), and MVQ-FKM blends with different compositions were investigated before and after aging. The rheometric study showed that optimum cure properties were obtained using the curing system of dicumyl peroxide (DCP) and triallylisocyanurate (TAIC). From varying the curing agents, the optimum levels of DCP and TAIC were found to be 2.0 phr and 1.5 phr, respectively. The addition of different fillers and their loading influenced the cure behaviors, with increased torque and scorch time compared with that of gum blends. The filled 50:50 (w/w) MVQ-FKM blends showed overall performance in mechanical properties. Post-curing improved the strength of MVQ-FKM blends, especially the blends with a higher proportion of FKM. Swelling of the blends was reduced with the addition of fillers and the increased incorporation of FKM. Dynamic mechanical analysis showed two tan δ peaks corresponding to MVQ and FKM phase for filled blends, respectively. The storage modulus of the blends increased with the addition of fumed silica, indicating the presence of polymer–filler interaction.

Steady rheological behaviors of UV-curable waterborne hyperbranched polyurethane acrylate dispersions

A rotational rheometer was used to investigate the steady rheological behaviors of UV-curable waterborne hyperbranched polyurethane acrylate dispersions (WHBPUADs). The flow curves of WHBPUADs were fitted mathematically using the Cross model. The effects of many factors including solid content, concentration of hydrophilic groups, and degree of neutralization on the rheological behaviors were studied and discussed. It was found that the viscosity of WHBPUAD decreased with increasing shear rate, indicating that WHBPUAD was pseudoplastic. On the other hand, at the same shear rate, the viscosity of WHBPUAD increased with increasing solid content and degree of neutralization but decreased with increasing concentration of hydrophilic groups. The Cross model could describe the flow curve of WHBPUAD accurately, with square of correlation coefficient (R2) above 0.9. Moreover, most of the zero-shear viscosity values (η0) obtained by the Cross model were located in the range of 0.2–10xa0Pa·s, which could fully meet the practical application requirement.

FT-IR and 29Si-NMR Studies on UV-Curable DDS-MPTMS/SiO2 Hybrid Coating

Ultraviolet (UV)-curable DDS-MPTMS/SiO2 hybrid coating was prepared by sol-gel process from tetraethylorthosilicate (TEOS), dimethyl diethylorthosilicate (DDS), and methacrylate propyl trimethoxysilicate (MPTMS). The formation of inorganic–organic hybrid network was studied by FT-IR and 29Si-NMR during UV curing. It was found that the three-dimensional (3D) inorganic networks were formed mainly by condensation of TEOS, and the linear Si-O-Si bonds were also formed by condensation of DDS. The organic networks were formed by the polymerization of C˭C bonds in methacrylate units and the silanol groups were further condensed when the hybrid coating was cured by UV light. The steric hindrance of organic–inorganic hybrid networks resulted in incomplete polymerization and condensation. When the UV curing time was 240 s, the conversion degree of C˭C bonds was 81.0% and the condensation degree of silanol groups in TEOS and MPTMS was 81.8% and 91.5%, respectively.