Structure-property relationship of castor oil based diol chain extended polyurethanes (PUs)

A series of 1,4-butane diol and 1,6-hexane diol based chain extended polyurethanes (PUs) have been prepared using castor oil with different diisocyanates such as methylene bis (phenyl isocyanate) (MDI), toluene-2,4-diisocyanate (TDI) and hexa methylene diisocyanate (HMDI) as crosslinkers. The prepared aliphatic diol based chain extended PU's have been characterised for physico-mechanical properties such as density, tensile strength, percentage elongation at break, tensile modulus and surface hardness; and optical properties like total transmittance and haze. The properties imparted by the chain extenders and diisocyanates on PUs have been explained on the basis of chemical structure. Effect of heat aging on mechanical properties of PUs have also studied. These changes have been interpreted quantitatively in terms of microcrystalline parameters computed using wide-angle X-ray scattering (WAXS) data.     

Structure-property relationships in graphitic cast irons

Some techniques used to study fatigue of cast irons are discussed and used to study the structure-property relationships in graphitic cast irons. A wide range of cast irons have been assessed to give a better understanding of the effects of metallurgical structure and graphite morphology on the fatigue behaviour of these materials. It is concluded that the ‘true’ fatigue strength reduction factor is one of the most significant parameters by which to consider improvements in fatigue properties. Increasing the amount of spheroidal graphite is suggested as a method of improving the fatigue properties of CG cast irons and yielding alloys with great potential importance.     

Structure-property relationships in polyimide molecular composites

Rigid rod-like polyimide (PI_R) / flexible-chain polyimide (PI_F) molecular composites, with 20, 40, 50, 60 and 80 wt. % of the rigid component, were prepared and their structure and molecular dynamics were investigated, in relation to those in pure PI_R and PI_F. SAXS, DSC, DMA, TSDC and laser-interferometric creep rate spectroscopy (CRS) techniques were used for characterization of nanostructure, glass transition and sub-T _g relaxations at temperatures from 100 to 600–650 K. All the experiments indicated pronounced deviations from additivity in both nanostructure and dynamics of molecular composites. Mixing of the PI_R and PI_F components led in particular to a smaller nanostructure, down to formation of the nanoscale-homogeneous composite. Changes of the dynamic characteristics in two opposite directions and arising of large dynamic heterogeneity around T _g were observed as a result of confinement/constraining effects. Received: 19 November 2001 / Reviewed/Accepted: 7 December 2001     

Structure-property relationships in heteroepitaxial InAs and InSb thin films

Heteroepitaxial thin films of InSb and InAs were evaporated onto sapphire and onto semi-insulating GaAs substrates. An in-line high vacuum evaporation set-up was used to deposit the semiconductor films by the three-temperature method at an ambient pressure of about 10^-5 mbar. The orientation and structure of the films were investigated as functions of substrate temperature and substrate orientation.The highest carrier mobilities were observed in (100)-oriented InAs and InSb films deposited on GaAs (100) substrates; these films had room temperature mobilities of 20 000 and 40 000 cm² V^-1 s^-1 respectively. InAs films on (0001) sapphire planes always showed (111) orientation with a maximum carrier mobility of 13 000 cm² V^-1 s^-1 at room temperature.     

Structure-property relationships in heterophasic thermoplastic elastomers filled with montmorillonite

Polypropylene (PP)/ethylene-propylene rubber (EPR)/Montmorillonite ternary nanocomposites with a phase separated morphology were studied in this work. Wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to investigate the samples. One of the aim of this work was to separate the effects of rubber and clay content on the structure, morphology and mechanical properties of the samples. The presence of clay favored the formation of gamma phase and disrupted the lamellar framework. Clay had moreover a major role in shaping the phase separated morphology of the samples. Atomic Force Microscopy showed that the shear exerted by the clay layers was key for inducing a shish kebab morphology in the polymer matrix. Rubber content decreased the degree of crystallinity at a crystalline cell level and induced the formation of a double population of lamellar stacks. The mechanical properties of the samples primarily depended on rubber content, and they were secondarily tuned by the effect of clay. This synergistic effect allowed to obtain composites with increased stiffness, ductility and toughness, oppositely to what is frequently found.     

Structure-property relationships of electroluminescent polythiophenes: role of nitrogen-based heterocycles as side chains

A series of conjugated polythiophenes containing nitrogen-containing heterocycles as side chain, with differing substituent nature and linkage have been studied using quantum-chemical calculations. The optical properties of synthesized polymers were compared with that of model compounds with intricate structural variations. The theoretically predicted optical characteristics are correlated with the experimentally determined parameters. Experimentally determined band gap and absorption maxima found to follow the predicted trends. Single emissive layer polymeric light emitting diodes are fabricated and the structural influence on photo- and electro-emission was studied in detail. The study shows that the nature of side chain substituent such as number/position of nitrogen atoms and mode of linking of side chain plays a crucial role in deciding the geometry which in turn controls the voltage response of the electroluminescence.     

Structure–property relationships in polyurethanes derived from soybean oil

Two types of soy polyols have been prepared, one with secondary OH groups resulted from epoxidation of soybean oil followed by methanolysis (polyol type I) and the other with primary OH groups created from hydroformylation of soybean oil followed by hydrogenation (polyol type II). Cast polyurethane resins were prepared from these two types of polyols with Isonate 2143L, and rigid polyurethane foams were prepared from a blend of soy polyol and glycerol with PAPI 2901. Polyol II is much more reactive than polyol I towards polyurethane formation. This is evidenced from studies on polyurethane gel-times, glass transitions and rigid foam mechanical strengths. The reaction for the polyurethane formation is more complete for polyol II resulted from its higher reactivity than polyol I, although a less rigid polyurethane material is resulted from polyol II than from polyol I. Polyol type II also requires lower amounts of catalysts for rigid foam formulation. Both rigid foam systems produce foams having the required mechanical strength. The polyol II foam system behaves much like conventional rigid foam systems where the strength are proportional to system OH content, while the less reactive polyol I system does not.     

Structure-property relationships in isotactic poly(propylene)/ethylene propylene rubber/montmorillonite nanocomposites

Nanocomposites based on isotactic polypropylene/ethylene propylene rubber (iPP/EPR) were prepared adding different amounts of montmorillonite and maleated polypropylene. The structure and morphology of the samples were characterized by small angle X-ray scattering, wide angle X-ray diffraction, electronic and optical microscopy and differential scanning calorimetry, iPP showed a polymorphic behavior. Clay disrupted the ordered crystallization of iPP and had a key role in shaping the distribution of iPP and EPR phases: larger filler contents brought about smaller, less coalesced and more homogeneous rubber domains. Clay distributed itself only in the continuous phase and not in the rubber domains. Tactoids persisted on the surface of the sample, while delamination proceeded to a greater degree in the bulk of the materials. Melt flow rate, impact strength, flexural and tensile properties, were also measured and a structure-property correlation was sought. Clay produced its most significant effect on physical-mechanical properties by controlling the size of rubber domains in the heterophasic matrix. This allowed to obtain nanocomposites with increased stiffness and impact strength, a remarkable achievement for polymer layered-silica nanocomposites that usually suffer the drawback of being stiffer than the unfilled matrix, but at the same time with a lower resistance to impact. A beneficial effect of clay on thermal stability was also observed.     

Synthesis and characterization of BHETA based new polyurethanes

Recycling of polyethylene terephthalate (PET) by aminolysis breeds environmental benefits. In this work Polyethylene terephthalate in the form of waste fibers were subjected to depolymerization through aminolysis using excess amount of ethanolamine in the presence of sodium acetate, as catalyst. Obtained product, bis (2‐hydroxy ethylene) terephthalamide (BHETA) was in its pure form with sufficiently high yields. The purified product was characterized by FTIR, ¹HNMR and ¹³CNMR spectroscopy as well as melting point determination. Since catalyst and raw materials have low price, synthesis of this material is economical and could be used as diol to synthesis of polyurethanes. In this search, polyurethanes have been synthesized based on BHETA, HDI and polyethylene glycol via prepolymer method. Termogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) were carried out to study thermal stability, thermal transitions, T_m and T_g of synthesized polyurethanes. Effect of BHETA content in the main chain of synthesized polyurethanes on thermal stability of polyurethanes, strength and stiffness has been evaluated. BHETA based polyurethanes show Young's modulus about 300 MPa and elongation at break as 130% due to its aromatic structure.     

Isosorbide based chiral polyurethanes: optical and thermal studies

A new class of chiral polyurethanes containing amido linkages in the polymer backbone have been synthesized by reacting toluene diisocyanate with isosorbide (IS) chiral moiety and the chromophores [N,N′-ethane-1,2-diyl bis(6-hydroxy hexanamide), N,N′-butane-1,4-diyl bis(6-hydroxy hexanamide) and N,N′-hexane-1,6-diyl bis(6-hydroxy hexanamide)]. The corresponding chromophores were obtained by the aminolysis of ε-caprolactone by using the diamines, diaminoethane, diaminobutane and diaminohexane, respectively. All the polymers were synthesized according to the symmetry conditions so as to obtain the non-centrosymmetric environment. A series of polyurethanes were synthesized by varying the chiral–chromophore composition. The polyurethanes developed were characterized by optical and thermal methods.     

Synthesis,mechanical, thermal and chemical properties of polyurethanes based on cardanol

Cardanol, an excellent monomer for polymer production, has been isolated from CNSL and allowed to react with formaldehyde in a particular mole ratio in the presence of glutaric acid catalyst to give high-ortho novolac resin. Such characterized polyol has been condensed with diphenylmethane diisocyanate to produce rigid polyurethane. A commercially available polyol, polypropylene glycol-2000 (PPG-2000), has also been condensed with diphenylmethane diisocyanate and polyol to produce tough polyurethane. These polyurethanes were characterized with respect to their resistance to chemical reagents and mechanical properties such as tensile strength, percentage elongation, tear strength and hardness. Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) were undertaken for thermal characterization.     

Structure-property correlation on AA 2219 aluminium alloy weldments

AA 2219 aluminium alloy is the material proposed for the construction of tanks for liquid cryogenic fuels like liquid oxygen and liquid hydrogen, in Indian launch vehicle programmes. To meet the material requirement, ISRO has developed the alloy AA 2219 indigenously on an industrial scale. Process development and structure-property correlation of auto TIG weldments of AA 2219 Al alloy reported in this paper establishes that postweld reaging of AA 2219 weldments in T62 condition enhances both strength and ductility.     

Structure-property relationships in the case of the degradation of massive poly(α-hydroxy acids) in aqueous media

Degradation of two lactic-glycolic copolymers, namely PLA37.5GA25 (75%dl-lactide and 25% glycolide in the feed) and PLA75GA25 (75%l-lactide and 25% glycolide) was investigatedin vitro using aqueous media to model physiological conditions. Various techniques were used to monitor the effects due to hydrolytic degradation including weighing, SEC (size-exclusion chromatography), potentiometry, cryometry, enzymatic assay, X-ray scattering,¹H-nuclear magnetic resonance and differential scanning calorimetry. It was found that degradation proceeded faster in the centre than at the surface of standard parallelepipedic specimens. This feature had already been found for PLA50 (poly(dl-lactic acid)). The degradation rates of PLA37.5GA25 and PLA75GA25 were compared and it was found that intrinsically amorphous PLA75GA25 crystallized as degradation proceeded, in contrast to PLA37.5GA25. The crystallization of PLA75GA25 was related to the preferential degradation at glycolic units, which led tol-lactic-enriched fragments susceptible to crystallize. No major differences were observed between ageing in iso-osmolar saline and pH 7.4 phosphate buffer. In contrast, in the case of PLA37.5GA25, distilled water favoured surface-centre differentiation, probably because of osmotic exchange related to the absence of ionic strength.     

Structure-property relationship of specialty elastomer-clay nanocomposites

The present work deals with the synthesis of specialty elastomer [fluoroelastomer and poly (styrene-b-ethylene-co-butylene-b-styrene (SEBS)]-clay nanocomposites and their structure-property relationship as elucidated from morphology studies by atomic force microscopy, transmission electron microscopy and X-ray diffraction and physico-mechanical properties. Due to polarity match, hydrophilic unmodified montmorillonite clay showed enhanced properties in resulting fluoroelastomer nanocomposites, while hydrophobic organo-clay showed best results in SEBS nanocomposites.     

Morphology and ionic conductivity of solid polymer electrolytes based on polyurethanes with various topological structures

Polyurethanes with linear, hyperbranched and comb-crosslinked structures were synthesized and were used to prepare solid polymer electrolytes. The polymer electrolytes were characterized by means of Fourier transform Raman spectroscopy, impedance spectroscopy (IS) and atomic force microscopy (AFM). The results showed that salt concentration significantly influences the morphology and conductivity of the three kinds of polyurethane/LiClO₄ system. When the mole ratios of the ether oxygen atom to lithium ion were controlled to be 12, 4 and 4 respectively for linear, hyperbranched and comb cross-linking polyurethane, the electrolytes typically displayed micro-phase separated morphology and the ionic conductivity also reached maxima respectively at 2.2 × 10^–7 S/cm, 2.8 × 10^–6 S/cm and 2.8 × 10^–5 S/cm at room temperature.     

Thermal and mechanical profile of cast films from waterborne polyurethanes based on polyether block copolymers

Environmental considerations have been the cause of increasing research and development of waterborne polymer systems for many different applications, particularly as coatings for several kinds of substrates. In this work, waterborne polyurethanes (WPU) based on block copolymers of ethylene glycol and propylene glycol (EG-b-PG), with 25% of EG segments, poly(propylene glycol), dimethylolpropionic acid, isophorone diisocyanate, and hydrazine, as chain extender, were obtained in the absence of organic solvent. Thermal stability, by thermogravimetry, and mechanical properties of cast films obtained from the aqueous dispersions were evaluated. The degradation process started above 200 °C for all samples. It was verified that the block copolymer improved the thermal resistance but diminished the mechanical resistance of the WPU materials.     

有机硅改性聚氨酯的性能研究

含硅聚醚与二异氰酸酯(TDI)反应,氨丙基三甲氧基硅烷进行封端,制得一种有机硅改性聚氨酯,通过红外光谱表征了聚氨酯的结构。探讨了各种因素对聚氨酯成膜物性能的影响。研究结果表明:R值为1.5,反应温度为35℃～40℃,自制硅醚:N210的比值为1∶7,封端率为10%时,所得的含硅聚醚聚氨酯的性能较好。     

基于动量动力学模型的行人关系分析

进行了行人行为分析及行人关系研究。考虑到在机器视觉领域大多数研究仅关注于目标行为分类与识别,而目标间因果关系判别研究较少,且现有理论停留在心理学领域中的因果关系表达,提出了一种基于动量动力学模型的目标间因果关系识别方法,用于实现行人间因果关系的识别及量化计算。该方法利用Cam shift算法获得目标在视频中的位置并依据因果概念,构建动量动力模型,然后基于动量动力模型进行因果关系判别,最后计算因果值。根据因果值范围识别出视频行人间的三种因果关系:导致、促进和阻碍。实验表明,上述方法可以在视频监控条件下识别两运动行人间的因果关系。