Effect of temperature and strain rate on the compressive behaviour of supramolecular polyurethane

Supramolecular polyurethanes (SPUs) possess thermoresponsive and thermoreversible properties, and those characteristics are highly desirable in both bulk commodity and value-added applications such as adhesives, shape-memory materials, healable coatings and lightweight, impact-resistant structures (e.g. protection for mobile electronics). A better understanding of the mechanical properties, especially the rate and temperature sensitivity, of these materials are required to assess their suitability for different applications. In this paper, a newly developed SPU with tuneable thermal properties was studied, and the response of this SPU to compressive loading over strain rates from 10−3 to 104 s−1 was presented. Furthermore, the effect of temperature on the mechanical response was also demonstrated. The sample was tested using an Instron mechanical testing machine for quasi-static loading, a home-made hydraulic system for moderate rates and a traditional split Hopkinson pressure bars (SHPBs) for high strain rates. Results showed that the compression stress-strain behaviour was affected significantly by the thermoresponsive nature of SPU, but that, as expected for polymeric materials, the general trends of the temperature and the rate dependence mirror each other. However, this behaviour is more complicated than observed for many other polymeric materials, as a result of the richer range of transitions that influence the behaviour over the range of temperatures and strain rates tested.

Influence of thermoplastic extrusion on the nutritive value of bovine rumen protein

This Study investigated the impact of thermoplastic extrusion on the nutritive quality of bovine rumen protein. Proximal composition, amino acid profile and in vivo true protein digestibility among rats were determined in raw (RBR) and extruded (EBR) rumen. Raw and extruded bovine rumen presented high percentages of protein (more than 95% on dry basis). Neither raw nor extruded proteins had any limiting amino acid, and the RBR and EBR amino acid scores were, respectively, 1.28 (leucine) and 1.25 (methionine plus cystine). Extrusion reduced significantly true protein digestibility from 97.7% to 93.1% (p < 0.001), but protein digestibility-corrected amino acid scores for both proteins (RBR and EBR) were 100%. Animal growth presented comparable profiles using raw and extruded rumen. In conclusion, thermoplastic extrusion did not affect the protein quality of bovine rumen, and this does not hinder the use of this material as a food ingredient. (C) 2009 Elsevier Ltd. Ail rights reserved.

Cassava bagasse cellulose nanofibrils reinforced thermoplastic cassava starch

Cellulose cassava bagasse nanofibrils (CBN) were directly extracted from a by-product of the cassava starch (CS) industry, viz. the cassava bagasse (CB), The morphological structure of the ensuing nanoparticles was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), presence of other components such as sugars by high performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) experiments. The resulting nanofibrils display a relatively low crystallinity and were found to be around 2-11 nm thick and 360-1700 nm long. These nanofibrils were used as reinforcing nanoparticles in a thermoplastic cassava starch matrix plasticized using either glycerol or a mixture of glycerol/sorbitol (1:1) as plasticizer. Nanocomposite films were prepared by a melting process. The reinforcing effect of the filler evaluated by dynamical mechanical tests (DMA) and tensile tests was found to depend on the nature of the plasticizer employed. Thus, for the glycerol-plasticized matrix-based composites, it was limited especially due to additional plasticization by sugars originating from starch hydrolysis during the acid extraction. This effect was evidenced by the reduction of glass vitreous temperature of starch after the incorporation of nanofibrils in TPSG and by the increase of elongation at break in tensile test. On the other hand, for glycerol/sorbitol plasticized nanocomposites the transcrystallization of amylopectin in nanofibrils surface hindered good performances of CBN as reinforcing agent for thermoplastic cassava starch. The incorporation of cassava bagasse cellulose nanofibrils in the thermoplastic starch matrices has resulted in a decrease of its hydrophilic character especially for glycerol plasticized sample. (C) 2009 Elsevier Ltd. All rights reserved.

A Graphite-Polyurethane Composite Electrode for the Analysis of Furosemide

A graphite-polyurethane composite electrode has been used for the determination of furosemide, a antihypertensive drug, in pharmaceutical samples by anodic oxidation. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrooxidation process at +1.0 V vs. SCE over a wide pH range, with the result that no adsorption of analyte or products occurs, unlike at other carbon-based electrode materials. Quantification was carried out using cyclic voltammetry, differential pulse voltammetry, and square-wave voltammetry. Linear ranges were determined (up to 21 mu mol L-1 with cyclic voltammetry) as well as limits of detection (0.15 mu mol L-1 by differential pulse voltammetry). Four different types of commercial samples were successfully analyzed. Recovery tests were performed which agreed with those obtained by spectrophotometric evaluation. The advantages of this electrode material for repetitive analyzes, due to the fact that no electrode surface renewal is needed owing to the lack of adsorption, are highlighted.

Effect of polyol excess on the electrical property of vegetable-polyurethane film

Freestanding castor oil-based polyurethane (PU) film was obtained using spin-coating method. The effect of polyol content was analysed by means of thermally stimulated depolarisation current and AC dielectric measurements techniques. Two relaxation peaks were observed in the temperature range of -40 to 60 degrees C for PU with different polyol contents. The presence of polyol excess provides a shift to lower temperature of the a relaxation and the decrease in the activation energy of the transition in this region might be attributed to the plasticising effect of the polyol. The peak at higher temperature is due to the Maxwell-Wagner-Sillars relaxation, which also shifts in the low temperature direction as the polyol content is increased.

Characterization of Polyurethane Resins by FTIR, TGA, and XRD

Fourier Transformed Infrared Spectroscopy, Thermogravimetric Analysis, and X-ray Diffractometry have been used to investigate the rigid, semi rigid, and soft polyurethane (PU) forms, which were developed by the Group of Analytic Chemistry and Technology of Polymers - USF - Sao Carlos. The -NCO/-OH ratios were 0.6, 0.5, and 0.3% for rigid, semi rigid, and soft PUs, respectively, showing that different ratios cause differences in thermal behaviors and crystalline structures of the synthesized PU resins. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 263-268, 2010

Electrochemical Behavior of Verapamil at Graphite-Polyurethane Composite Electrodes: Determination of Release Profiles in Pharmaceutical Samples

A solid graphite-polyurethane composite electrode has been used to determine release profiles of verapamil, a calcium-channel blocker. The electro-oxidation process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy and showed no adsorption of analyte or oxidation products, unlike at other carbon-based electrodes. Quantification gave linear ranges up to 40molL-1 with cyclic voltammetry and detection limits of 0.7molL-1 by differential pulse and square-wave voltammetry. Commercial product samples were successfully analyzed with results equal to those from spectrophotometry. Because no electrode surface renewal is needed, this electrode material has many advantages.

Self-crimping bicomponent nanofibres electrospun from polyacrylonitrile and elastomeric polyurethane

Two polymer solutions were brought together via a microfluidic device and subjected to an electrospinning process. The two polymer solutions flowed into the microfluidic channel side-by-side with very little intermixing due to their laminar nature. High speed stretching of the polymer solutions resulted in side-by-side bicomponent fibres. The electrospun nanofibres exhibited an extremely high propensity to self-crimp when an elastomeric polymer (polyurethane) and a normal polymer (polyacrylonitrile PAN) were involved in the electrospinning process. The formation of self-crimping fibre morphology was attributed to the differential shrinkage of the two polymers.

Toughened electrospun nanofibers from crosslinked elastomer-thermoplastic blends

A crosslink-able elastomeric polyester urethane (PEU) was blended with a thermoplastic, polyacrylonitrile (PAN), and electrospun into nanofibres. The effects of the PEU/PAN ratio and the crosslinking reaction on the morphology and the tensile properties of the as-spun fibre mats were investigated. With the same overall polymer concentration (9 wt %), the nanofibre containing higher composition of PEU shows a slight decrease in the average fibre diameter, but the tensile strength, the elongation at break and tensile modulus of the nanofibre mats are all improved. These tensile properties are further enhanced by slight crosslinking of the PEU component within the nanofibres.

Small diameter Polyurethane vascular graft reinforced by elastic weft-knitted tubular fabric of polyester / spandex

Small diameter vascular grafts were fabricated from pure Polyurethane (PU) as well as PU reinforced with a tubular weft-knitted fabric. The tensile properties of the reinforced composite vascular grafts were compared with that of the tubular fabric itself and the pure PU vascular grafts. The elasticity and strength of the reinforced vascular grafts were improved compared with the tubular fabric. Strength of the reinforced vascular grafts was 5–10 times of the strength of the pure PU vascular grafts. Expanding the tubular fabric to increase the inner diameter of the reinforced vascular graft reduced the graft’s strength and initial modulus, but the difference was reduced as the PU content was increased. For grafts of the same inner diameter, increasing the PU content increased the thickness and strength of the graft wall, which led to a general increase in the strength and initial modulus of the composite vascular grafts.

Thermoplastic film from superfine wool powder

In this paper a research work is described in which superfine wool powder was plasticised by glycerol and hot-pressed into a kind of thermoplastic film. SEM photos show that the powder is moulded into a smooth surface and is conglutinated into a continuous phase in the cross-section of the film. The glycerol content, moulding pressure, temperature and moulding time were changed in the moulding process. The sizes and thickness aw well as tensile strength, modulus, breaking elongation and breaking energy of the films were also tested to investigate the thermoplasticity and mechanical properties of the films. The best moulding techniques included a glycerol content of 30%, a moulding pressure of 5 MPa, a temperature of 160 °C and a moulding time of 5 minutes.

Structural and material properties of a rapidly cured thermoplastic-toughened epoxy system

Thermoplastic-toughened epoxy resins are widely used as matrices in modern composite prepreg systems. Rapid curing of thermoplastic-toughened epoxy matrix composites results in different mechanical properties. To investigate the structure–property relationship, we investigated a poly(ether sulfone)-modified triglycidylaminophenol/ 4,4'-diamino diphenyl sulfone system that was cured at different heating rates. An intermediate dwell was also applied during the rapid heating of the thermoplasticmodified epoxy system. We found that a higher heating rate led to a larger domain size of the phase-separated macrostructure and also facilitated more complete phase separation. The intermediate dwell helped phase separation to proceed even further, leading to an even larger domain size of the macrostructure. A carbon-fiber-reinforced polymer matrix composite prepreg based on the poly(ether sulfone)-modified multifunctional epoxy system was cured with the same schedule. The rapidly heated composite laminates exhibited higher mode I delamination fracture toughness than the slowly heated material.

Study on thermoplastic-modified multifunctional epoxies : influence of heating rate on cure behaviour and phase separation

The effect of heating rate on the cure behaviour and phase separation of thermoplastic-modified epoxy systems was investigated. Polyethersulphone (PES) modified multifunctional epoxies, triglycidyl-aminophenol (TGAP) and tetraglycidyldiaminodiphenylmethane (TGDDM), as well T300/914 prepreg were used. It was shown that heating rate had a significant influence on the cure kinetics and phase structures of investigated systems. Greater heating rate causes higher epoxy conversion. The domain size of the macrophases formed from phase separation increases with the increase of heating rate. A more complete phase separation is achieved by fast heated thermoplastic-modified epoxy blends.

Endothelialisation and cell retention on gelation-chitosan coated electrospun polyurethane, poly (lactide-co-glycolide) and collagen-coated pericardium

Arterial bypass and heart valve replacements are two of the most common surgical treatments in cardiovascular surgery today. Currently, artificial materials are used as substitute for these cardiac tissues. However, these foreign materials do not have the ability to grow, repair or remodel and are thrombogenic, leading to stenosis. With the aid of tissue engineering, it is possible to develop functional identical copies of healthy heart valves and arteries, which are biocompatible. Although much effort has been made into this area, there are still inconsistencies with respect to
endothelialisation and cell retention on synthetic biological grafts. These variations may be attributed to differences in factors such as cell seeding density, incubation periods and effects of shear stress. In this study, we have compared the endothelialisation and cell retention between gelain chitosan-coated electrospun polyurethane (PU), poly (lactide co-glycolide) (PGA/PLA) and collagen-coated pericardium. Endothelial cells adhered to all of the materials as early as 1–day post seeding. After 7-day of seeding, the coverage on PU was almost 45% and that on PGA/PLA was about 25% and the least was on collagen-coated pericardium of approximately 15%. It was observed that the PU showed superior cell coverage and cell retention in comparison to the PGA/PLA and collagen-coated pericardium.

Modification of thermoplastic coatings for improved cathodic disbondment performance on a steel substrate : a study on failure mechanisms

The effect of blending two different materials with a medium density polyethylene for use as pipe coatings is presented. The influence of such blending on properties such as cathodic disbondment (CD) and wet adhesion on steel is investigated. The components blended include a functionalised polyethylene (PE) containing the polar functionality, maleic anhydride (MAH) and an amorphous elastomer, ethylene-propylene-diene terpolymer (EPDM). It was found that modification of PE with small amount (2.5–3 wt%) of either blended MAH-g-PE or EPDM resulted in a significant improvement in CD performance and wet adhesion strength. The mode of failure and disbondment mechanism was investigated using energy dispersive X-ray spectroscopy (EDXS) and X-ray photoelectron spectroscopy (XPS). The greater resistance of migration of sodium ions increases with the incorporation of the modifiers, and it is proposed that this results in an increase in CD performance.