The structure–property relationships of urethane-acrylic thermosetting systems

Urethane-acrylic copolymers have found increasing use as a radiation curable materials in the recent years. These copolymers are highly crosslinked through the use of acrylic monomers having more than one double bond. Stirling Lloyd had discovered such materials to be a successful alternative to the urethane or acrylics coatings as waterproof membrane coatings. In this project, structure-property relationships of UA copolymer systems were studied. These were peroxide cured at room temperature. [Continues.

In situ dispersion of lignin in polypropylene via supercritical CO₂ extrusion foaming: effects of lignin on cell nucleation and foam compression properties

Supercritical CO2 (scCO2) extrusion foamed high-melt-strength (HMS) polypropylene (PP) often suffers from low cell density, large cell sizes, and poor cell structure uniformity due to the poor nucleation rates of CO2 in the PP. To remedy this, various inorganic fillers have been used as heterogeneous nucleation agents. Although their efficient nucleation effects have been demonstrated, the preparation of these fillers causes some adverse effects on the environment/human health or involves relatively expensive processes or non-eco-friendly chemicals. In this work, biomass-based lignin is studied as a sustainable, lightweight, and cost-effective nucleating agent. It is found that scCO2 could assist in situ dispersion of lignin in the PP in the foaming process, leading to significantly increased cell density, smaller cells, and improved cell uniformity. The Expansion Ratio is also simultaneously improved due to reduced diffusive gas loss. The PP/lignin foams with low lignin loadings exhibit higher compression moduli and plateau strengths than the PP foams with the same densities owing to the improved cell uniformity and probably also the reinforcing effect of the small lignin particles in cell walls. Moreover, the energy absorption capability of the PP/lignin foam with 1 wt% lignin could match the PP foam with similar compression plateau strengths; even the density of the former is 28% lower than the latter. Therefore, this work provides a promising approach to a cleaner and more sustainable production of HMS PP foams.Published versio

Interfacial stabilizing and reinforcing effects of silsesquioxane-based hybrid Janus molecules in extrusion supercritical CO₂ foaming of polypropylene

High-melt-strength (HMS) polypropylene (PP) has enabled easy supercritical-CO2 (scCO2) foaming of PP. However, producing microcellular PP foams via simple scCO2 extrusion foaming still remains challenging, whereas macrocellular PP foams with high expansion ratios (ER) generally exhibit poor mechanical strengths. In this study, to simultaneously enhance both ER and compressive strengths of macrocellular PP foams, a type of low-cost Janus molecules, heptaisobutyl open-cage silsesquioxane (HOS), is incorporated into HMS-PP. Since HOS has PP-philic groups and a partially condensed silsesquioxane cage that is relatively CO2-philic, it could diffuse like a surfactant to the PP-CO2 interface during scCO2 extrusion foaming to stabilise the cells in their growth stage and reinforce the cell surface upon solidification. The surfactant effect is validated via X-ray Photoelectron Spectroscopy. Moreover, with 1 wt% HOS, the PP/HOS foam could offer 38 % ER improvement, 23 % density reduction, and 20 % compressive strength increase over the neat PP foam. HOS could also slightly improve the extensional viscosity and melt strength of PP at ≤1 wt% loadings and reduce the shear viscosity of PP by acting as a lubricant. This approach provides a simple and economically viable materials design guideline for alleviating ER-compression strength trade-offs for macrocellular polymer foams.Agency for Science, Technology and Research (A*STAR)Nanyang Technological UniversityPublished versionHo Keen Hoe thanks Singapore Institute of Manufacturing Technology (SIMTech), Agency for Science, Technology and Research for providing his PhD scholarship. The authors thank Nanyang Technological University and SIMTech for providing financial support in the course of this work

The other face of the acquisition : a study of the integration issues arising from DBS' acquisition of POSBank.

This paper examines the process whereby a "public service" bank is transformed into a commercial entity through an acquisition of POSBank by DBS.Master of Business Administration (Strategic Management

Poly(ethylene terephthalate)/clay nanocomposites with trisilanolphenyl polyhedral oligomeric silsesquioxane as dispersant : simultaneously enhanced reinforcing and stabilizing effects

This paper presents a new approach for the preparation of poly(ethylene terephthalate) (PET)/clay nanocomposites using surfactant-free clay (sodium montmorillonite, Na-MMT) with trisilanolphenyl polyhedral oligomeric silsesquioxane (Tsp-POSS) as dispersant. The dispersion of clay in the PET/Na-MMT/Tsp-POSS nanocomposites is enhanced over that in PET/Na-MMT by using a very small amount of Tsp-POSS, which acts as functional spacer to keep clay platelets apart and pull monomers in, and, at the same time, acts as a PET chain extender. As a result, thermomechanical properties and thermo-oxidative stability of PET/Na-MMT/Tsp-POSS are improved simultaneously compared with those of PET/organoclay nanocomposites.ASTAR (Agency for Sci., Tech. and Research, S’pore

Fracture Toughness and Elastic Modulus of Epoxy-Based Nanocomposites with Dopamine-Modified Nano-Fillers

This paper examines the effect of surface treatment and filler shape factor on the fracture toughness and elastic modulus of epoxy-based nanocomposite. Two forms of nanofillers, polydopamine-coated montmorillonite clay (D-clay) and polydopamine-coated carbon nanofibres (D-CNF) were investigated. It was found that Young’s modulus increases with increasing D-clay and D-CNF loading. However, the fracture toughness decreases with increased D-clay loading but increases with increased D-CNF loading. Explanations have been provided with the aid of fractographic analysis using electron microscope observations of the crack-filler interactions. Fractographic analysis suggests that although polydopamine provides a strong adhesion between the fillers and the matrix, leading to enhanced elastic stiffness, the enhancement prohibits energy release via secondary cracking, resulting in a decrease in fracture toughness. In contrast, 1D fibre is effective in increasing the energy dissipation during fracture through crack deflection, fibre debonding, fibre break, and pull-out.ASTAR (Agency for Sci., Tech. and Research, S’pore)Published versio

Reinforcement of polyether polyurethane with dopamine-modified clay : the role of interfacial hydrogen bonding

Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures

Shape memory polyurethane with polydopamine-coated nanosheets: Simultaneous enhancement of recovery stress and strain recovery ratio and the underlying mechanisms

Two different sizes of polydopamine-coated layered double hydroxides (D-LDHs) are incorporated into polycaprolactone-based polyurethane (PU) to enhance the mechanical and shape memory properties of the PU. The results show that D-LDH interacts strongly with hard segments and hence enhancing phase separation between hard and soft segments. It is found that the tensile moduli of the PU/D-LDH nanocomposites are much higher than that of neat PU at 60 oC. In comparison with neat PU, the nanocomposite with 2 wt% of small D-LDH exhibits a 60% increase in recovery stress while shape fixity and strain recovery ratio are also improved simultaneously. This is because at low filler loading, most small D-LDH nanosheets interact with hard domains and they are not large enough to connect neighbor hard domains. They can hence reinforce the hard domains without sacrificing the elasticity of the system. Two-dimensional X-ray diffraction studies indicate that most small D-LDH nanosheets are able to rotate back from aligned state to original random state in shape recovery process, justifying the improved strain recovery ratio.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio

Simultaneous Enhancements of UV Resistance and Mechanical Properties of Polypropylene by Incorporation of Dopamine-Modified Clay

Inspired by the radical scavenging function of melanin-like materials and versatile adhesive ability of mussel-adhesion proteins, dopamine-modified clay (D-clay) was successfully incorporated into polypropylene (PP) using an amine-terminated PP oligomer as the compatibilizer. Although the PP/D-clay nanocomposites exhibit intercalated morphology, the incorporation of D-clay greatly improves the thermo-oxidative stability and UV resistance of PP owing to the strong radical scavenging ability of polydopamine (PDA) and large contact area between PP and the PDA coating on clay mineral. Moreover, the reinforcement effect brought by D-clay is fairly significant at very low clay loadings probably owing to the strong interfacial interactions between the layered silicates and the compatibilizer as well as that between the compatibilizer and the PP matrix. The work demonstrates that D-clay is a type of promising nanofiller for thermoplastics used for outdoor applications since it stabilizes and reinforces the polymers simultaneously

Reinforcement of Polyether Polyurethane with Dopamine-Modified Clay: The Role of Interfacial Hydrogen Bonding

Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures