Damping,Thermal, and Mechanical Properties of Polycaprolactone-Based PU/EP Graft IPNs: Effects of Composition and Isocyanate Index

A series of polycaprolactone (PCL)-based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer networks (IPNs) were prepared and their damping propertiesand thermal stability, as well as mechanical properties, were systematically studied in terms of composition and the values of the PU isocyanate index (R). The morphologies of the PU/EP IPNs were observed by scanning electron microscope (SEM) and atomic force microscope (AFM) characterization and the relationship between the morphologies and the properties is also discussed. The damping properties and thermal stability measurements revealed that the formation of PU/EP IPNs could significantly improve not only the damping properties but also the thermal stability. Meanwhile, the mechanical tests showed that the tensile strengths of the IPNs decreased, while their impact strengths increased with increasing PU content. The value of the PU isocyanate index also had significant impacts on the properties of the IPNs when the PU to EP ratio was fixed, which could be an effective means for manipulating the fabrication of PU/EP IPNs. From the results obtained, the PCL-based PU/EP IPNs hold promise for use in structural damping materials.     

Physical properties of a high molecular weight hydroxyl-terminated polydimethylsiloxane modified castor oil based polyurethane/epoxy interpenetrating polymer network composites

A series of polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The effects of HTPDMS content on the phase structure, damping properties and the glass transition temperature (Tg) of the HTPDMS-modified PU/EP IPN composites were studied by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of the composites increased with the increase of HTPDMS content. The tensile strength and impact strength of the IPN composites were also significantly improved, especially when the HTPDMS content was 10%. The modified IPN composites were expected to be used as structural damping materials in the future.     

Castor Oil-Based Polyurethane/Epoxy Intercross-linked Polymer Network Adhesives for Metal Substrates

Castor oil based polyurethane (CO-PU) was first synthesized from castor oil and 4, 4’-diphenyl-methane-diisocyanate (MDI). Then, a series of CO-PU/epoxy (EP) intercross-linked polymer network (ICPN) adhesives for metal substrates were prepared by a sequential method. The functional groups, tack -free time, mechanical properties, adhesive properties, and thermal stability were studied. Fourier transform infrared spectroscopy analysis indicated that an ICPN structure was formed through the introduction of CO-PU into EP. Results of adhesive measurements showed that the maximal value of lap shear strength was achieved at the CO-PU content of 20%. Thermogravimetric analysis results indicated that thermal stability of the adhesive film decreased with increased CO-PU content.     

Synergistic Effect of Polyhedral Oligomeric Silsesquioxane and Multiwalled Carbon Nanotubes on the Flame Retardancy and the Mechanical and Thermal Properties of Epoxy Resin

A novel polyhedral oligomeric silsesquioxane containing phosphorus and boron (PB-POSS) was synthesized. The resulting PB-POSS and multiwalled carbon nanotubes (MWCNTs) were incorporated into an epoxy resin (EP) to prepare PB-POSS/MWCNTs/EP composites through a solution mixing method. The synergistic effect of MWCNTs and PB-POSS on the thermal and mechanical properties and the flame retardancy of these flame retardant composites were studied. The experimental results showed that the introduction of PB-POSS or MWCNTs further improved the LOI values of the epoxy resin, and the highest LOI value (32.8%) was obtained for the formulation containing 14.6 wt% PB-POSS and 0.4 wt% MWCNTs. In addition, the incorporation of both PB-POSS and MWCNTs significantly improved the thermal and mechanical properties of the composites. The mechanical properties of composites containing 14.7 wt% PB-POSS and 0.3 wt% MWCNTs reached the maximum. The impact strength and flexural strength increased by 42% and 7%, respectively, compared to the neat epoxy resin. Thus, a combination of PB-POSS and MWCNTs in the appropriate ratio could effectively enhance the thermal and mechanical properties and the flame retardancy of the epoxy resin matrix.     

Study of Electrical Conductivity of Para-Toluene Sulfonic Acid Doped Polyaniline/Polyester-Based Polyurethane Blends in the S-Band Frequency Range

Conducting polymer blends were prepared using polyaniline doped with para- toluene sulfonic acid (PTSA-PANI) and a polyester polyol-based polyurethane (PU). The morphological, thermal and dielectric properties of the PTSA-PANI/PU blends in the frequency range of 1–5 GHz (S band) were investigated. It was found that the morphology of the samples was affected by the PTSA-PANI loading, resulting in the formation of agglomerates and pathways when above 10 wt%. The thermal stability of the composites was improved with increased PTSA-PANI loading. The electrical conductivity percolation threshold was obtained at 2.5% of PTSA-PANI loading and the electrical conductivity reached the value of 0.13 S/m at a PTSA-PANI loading of 30 wt%. The obtained results for the PTSA-PANI/PU blends prepared indicate a high potential for their successful use in electrical and electromagnetic applications.     

Mechanical Properties,Rheology, and Crystallization of Epoxy-Resin-Compatibilized Polyamide 6/Polycarbonate Blends: Effect of Mixing Sequences

Blends of polyamide 6 (PA6)/polycarbonate (PC)/epoxy resin (EP) were melt blended with three different mixing sequences. Their mechanical properties, crystallization, and rheological behaviors, as well as the morphology, were investigated via mechanical testing, differential scanning calorimetry (DSC), dynamic rheometry, and scanning electron microscopy (SEM). It was noted that the mixing sequences affected the distribution of EP in the PA6 matrix, as well as the reactivity of EP with PA6 and PC. Mechanical testing showed that the blends prepared by the first (S₁, blending PA6, PC, and EP simultaneously) and second mixing sequences (S₂, blending PC with a premixture of PA6/EP) had higher notched Izod impact strengths due to the formation of PA6-EP-PC block copolymer (named as the AEC structure) during compounding, as evidenced by the results of dynamic rheology and SEM. Whereas for the third sequence (S₃, blending PA6 with a premixture of PC/EP), EP could barely react with PA6 and PC, leading to little formation of AEC structure, which resulted in a poor notched Izod impact strength of the blends. The incorporation of EP actually acted as a plasticizer to improve the elongation at break of the S₃ blends. In addition, the DSC results and SEM observations showed that there were distinct differences in the crystallization and morphology of the samples prepared by the different mixing sequences.     

Physical Properties of Micro Hollow Glass Bead Filled Castor Oil-Based Polyurethane/Epoxy Resin IPN Composites

A series of micro hollow glass beads (HGB) filled castor oil-based polyurethane/epoxy resin graft interpenetrating polymer network (IPN) composites were prepared. The tensile and impact strengths, impact fractured surfaces, damping properties and thermal stability of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of HGB into polyurethane/epoxy IPN can significantly improve not only the tensile strength but also the impact strength. The tensile strength was increased by 61% and at the same time the impact strength was increased by 25% when the HGB content was 1.5%. The damping properties were better than the composition of 0.5% or 2% HGB content when the HGB content was 1% or 1.5%. The thermal decomposition temperature was also slightly improved by the incorporation of HGB. It is suggested that the HGB reinforced polyurethane/epoxy resin IPN composites could be used as structural damping materials.     

Adhesion,morphology, and heat resistance properties of polyurethane coated poly(methyl methacrylate)/fullerene-C60 composite films

Novel polyurethane (PU) adhesive was prepared and coated on poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)/fullerene (PMMA/Full-C₆₀) composite. Dip-coating technique was employed as facile and cost-effective procedure to coat polyurethane on film substrate. The properties of PU/PMMA and PU/PMMA/Full-C₆₀ composite were studied using Fourier transform infrared spectroscopy, Field Emission Scanning Electron Microscopy, tensile, adhesion, thermal and flammability measurement. Testing polyurethane-coated PMMA exhibited crumpled surface while fullerene addition formed unique pattern of dispersed spherical structures. Fullerene nanofiller loading improved the adhesion and mechanical properties of composite films due to polymer–carbon interaction. In PU/PMMA/Full-C₆₀ 0.5 composite with 0.5 wt.% nanofiller, tensile strength (71.4 MPa) was increased by 18.6% while tensile modulus was increased by 143.85% compared with PU/PMMA. In PU/PMMA/Full-C₆₀ 0.5, T₀ of 473 °C and T_max of 655 °C were observed. Increasing the fullerene content up to 0.5 wt.% decreased the peak heat release rate to 131 kW/m². Novel polyurethane-coated PMMA/Full-C₆₀ composite have potential applications as adhesive coatings in electronic and automotive appliances.     

Tribological Properties of Hydroxyl-Terminated Liquid Nitrile Rubber-Modified Polyurethane/Epoxy Interpenetrating Polymer Network Composites

A series of castor oil-based polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by two kinds of hydroxy-terminated liquid nitrile rubber (HTLN) was prepared. A systematic investigation of the tribological properties of the two kinds of HTLN-modified PU/EP IPN composites was carried out through a pin-on-disk arrangement under dry sliding conditions. Experimental results revealed that the incorporation of HTLN can improve the friction and wear properties of PU/EP IPN significantly. Both the friction coefficient and wear loss decreased with increasing content of HTLN. The worn surfaces of the samples were analyzed using scanning electron microscope and a three-dimensional (3D) noncontact surface-mapping profiler; the results showed that the worn surfaces of the PU/EP IPN composites became smooth when the HTLN was added. The mechanisms for the improvement of tribological properties are discussed.     

Static and cyclic mechanical behaviours and fracture mechanisms of Zr-based metallic glass at elevated temperatures

To comprehensively understand the quantitative mechanical–thermal properties and fracture mechanisms of Zr-based bulk metallic glass (BMG), by using self-made miniature tensile/compressive device and motor-piezoelectric coupling driven fatigue device, a series of static and dynamic mechanical tests at elevated temperatures of bulk Zr₅₅Cu₃₀Al₁₀Ni₅ BMG with glass transition temperature T_g of 411°C were carried out. Uniaxial tensile and compressive behaviours at temperatures with range from RT to 400°C were experimentally obtained by means of digital speckle correlation analysis, the estimation of Young’s modulus and fracture strengths as a function of the applied temperatures were investigated. The static and cyclic fracture morphologies at various temperatures were obtained to describe the mechanical–thermal fracture mechanisms in detail. The coupling effect of loading types, stress-induced temperature rise and applied temperature on the evolution of cleavage features, dimples, vein patterns and shear softening behaviours were investigated.