Structure and properties of cross-linked polyurethane copolymers

Effect of Thermal Aging on the Physico-Chemical and Optical Properties of Poly(ester urethane) Elastomers Designed for Passive Damping (Pads) of the Railway

The aim of this study consists of monitoring the effect of thermal aging on the physico-chemical and optical properties of poly(ester urethane) elastomers designed as damping materials for railways. The materials were obtained by polyaddition in two stages in melt, resulting in regular structures. The structural modifications during the thermal aging of the samples were monitored using FTIR, color changes, TGA in non-isothermal and isothermal conditions, DSC and physico-mechanical measurements. The structural regularity of the rigid and flexible segments maintained the good mechanical properties of the structures up to 200 h of thermal aging at the elevated temperatures of 40 °C, 70 °C, 100 °C and 130 °C. It was observed that at 40 °C and low exposure times, changes occur mainly to the carbonyl groups of the soft segments. At higher temperatures and longer exposure times urethane groups were affected. Extended thermal aging led to significant changes in thermo-mechanical and optical properties.

Effect of γ irradiation on the impact response of rigid polyurethane foam

An experimental study to observe the change in impact response of rigid polyurethane foam due to γ irradiation is presented. The foam samples were irradiated using a 60Co based γ irradiator, γ Chamber 5000. Dynamic tests were performed on unirradiated and irradiated cubical foam specimens in a drop weight testing machine to characterize the mechanical properties. Structural characterization was performed using phase-contrast X-ray imaging and scanning electron microscopy (SEM). The results reveal a significant change in the dynamic response of polyurethane foam after irradiation due to change in structure. The response of foam gets stiffer in the initial linear phase, and densification (lockup) occurs well below the strains at which lockup occurs for an unirradiated foam. The ramifications of this study towards the application of polyurethane foam as an impact limiter in nuclear shipping casks are discussed.

Highly conductive and flexible chitosan based multi-wall carbon nanotube/polyurethane composite fibers

Chitosan-based CNT composite fibers have received much attention due to their biocompatibility and biodegradability.

Migration of non intentionally added substances from adhesives by UPLC-Q-TOF/MS and the role of EVOH to avoid migration in multilayer packaging materials

Polyurethane adhesives are commonly used to laminate multilayer packaging materials for food. Since these materials are in direct contact with the food, compounds could migrate from adhesive into it. For this reason, it is important to identify all the potential migrants and verify their migration. Ultra-high performance liquid chromatography-quadrupole time-of-flight-mass spectrometry analyses and ChemSpider database are used to identify the potential migrants from polyurethane adhesives, and these techniques were demonstrated to be very powerful and useful tools for this purpose. Migration tests were carried out using Tenax® as food simulant. Nine out of fifteen non-volatile compounds, identified in the cured adhesives, migrated. Most of them were identified as cyclic compounds, adipic based, which is the most commonly used monomer to make the polyester/polyol resins for polyurethane bi-component adhesives. In this work, the use of EvOH layer in several multilayer materials to minimize or avoid migration was evaluated too.

Design and characterization of novel β-cyclodextrin based copolymer materials

Reported herein are the systematic design and characterization of several novel polyurethane (PU) copolymers containing a macrocyclic porogen (β-cyclodextrin; β-CD). These copolymers were synthesized from the reaction between β-CD with different types of diisocyanate linker molecules (e.g., 1,6-hexamethylene diisocyanate (HDI), 4,4'-dicyclohexylmethane diisocyanate (CDI), 4,4'-diphenylmethane diisocyanate (MDI), 1,4-phenylene diisocyanate (PDI) and 1,5-naphthalene diisocyanate (NDI)) at variable synthetic conditions. The copolymers were characterized using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid state (13)C CP-MAS NMR, (1)H/(13)C solution NMR spectroscopy, thermogravimetric analysis (TGA) and elemental analyses (CHN). The PU copolymers were generally insoluble in water and the optimal preparation of copolymer materials for sorption-based applications is for β-CD/linker synthetic mole ratios from 1:1 to 1:3. The practical upper limit of the crosslink density (approximately 1:7, β-CD/linker) depends on the steric bulk of the cross linker units.