Structure‐property relationships in copolyester elastomer‐layered silicate nanocomposites

While the field of polymer–clay nanocomposites is reaching maturity, some parts of the studied systems still present researchers with possibilities for the improvement of material properties. This study entails the understanding of the relationships in copolyester elastomer/organically modified layered silicate nanocomposite and the structure–property relationships within the system of the nanocomposite. A series of these nanocomposites was prepared via twin‐screw extrusion melt compounding. The experiments included the following three types of synthetic organosilicates: high aspect ratio Somasif (ME100) fluoromica and two lower aspect ratio Laponite synthetic hectorites, (WXFN) and (WXFP). These organosilicates were modified with quaternary octadecyltrimethylammonium bromide (ODTMA) and were used to prepare the nanocomposites. The nanocomposite structure on a micro‐ and nanometre scales was evaluated by two techniques, such as X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of the nanocomposites were examined to determine the impact aspect ratio of the nanofiller and wt % loading have on performance. The addition of the 2 wt % high aspect ratio of ME100‐ODTMA, in particular, showed statistically improved tensile strength, tear resistance, creep resistance, and water vapor permeation barrier enhancement. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41742.     

Structure‐properties relationship in resol/montmorillonite nanocomposites

Polymer/layered silicate nanocomposites were prepared, adding modified, and nonmodified montmorillonites to a resol resin. It was observed that the composites exhibited an intercalated disordered structure by means of X‐ray diffraction (XRD) and transmission electronic microscopy. The crosslinking density of the resol network was greatly influenced by the presence and type of clay that was added to the resin. The composites filled with the modified montmorillonites showed a lower glass transition temperature value as well as a higher degradation peak at ～ 400°C, which is characteristic of the degradation of methylene bridges, indicating a decrease in the crosslinking density of the resol network when modified clays are added. Resol/unmodified montmorillonite composites exhibited different behavior comparing to the other composites and the resol. A higher thermal resistance was observed in the fragmentation zone and a different tan δ response was seen in the DMA analysis. These differences in the behavior of the composites could be because of the interaction between the resol prepolymer and the clay modifiers and as a result of their chemical compatibility. The hardness and elastic modulus of the resol were improved with the addition of clays. However, higher values were obtained for the composite made with the more dispersed montmorillonite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structure–property relationships of medium‐density polypropylene foams

This paper is focused on the production and characterization of a collection of polypropylene (PP) foams with relative densities ranging from 0.3 to 0.6. Samples were foamed using the improved compression moulding method. The process allows controlling density and cellular structure independently as well as obtaining PP foams without fillers, crosslinking or using special PP grades. The influence of blowing agent content, density, cellular structure and foaming conditions on the mechanical response measured in compression, tensile, bending and Charpy impact tests was determined. Results show that density, open cell content and blowing agent concentration have a significant influence on the mechanical performance of medium‐density PP foams. © 2013 Society of Chemical Industry     

Structure–property relationships in PVC compression moldings

Compression moldings were produced from two rigid PVC compounds at a range of temperatures. The tensile and impact properties of these moldings depended primarily on the level of particle fusion as assessed by extrusion rheometry. Properties were not related to the level of primary crystallization measured by X-ray diffraction, but the particle fusion process appears to be at least partly due to recrystallization. Fusion occurred more readily in the mass PVC compound than in the suspension PVC compound. Annealing the sheet produced at 200°C caused changes in crystallinity which resulted in small property changes. The maximum annealing effect occurred at 110°C.     

Photosensitive polynorbornene based dielectric. I. Structure–property relationships

In the microelectronics industry, the drive for increasing device speed, level of functionality and shrinking size has placed significant demands on the performance characteristics of polymer dielectrics. In this study, a negative acting, photodefinable dielectric formulation based on a copolymer of decylnorborne (decylNB) and epoxynorbornene (AGENB) was investigated for use in electronics packaging. The structure–property relations of this copolymer were investigated. Copolymer composition and processing conditions were shown to significantly affect the properties of the final polymer films. A lower content of AGENB results in lower moisture absorption, dielectric constant, modulus and residual stress, but it compromises multilayer capability. High crosslink density lowers the dielectric constant but increases the modulus and residual stress. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3023–3030, 2004     

Crystallization kinetics and melting behavior of nylon 10,10 in nylon 10,10–montmorillonite nanocomposites

The crystallization kinetics and melting behavior of nylon 10,10 in neat nylon 10,10 and in nylon 10,10–montmorillonite (MMT) nanocomposites were systematically investigated by differential scanning calorimetry. The crystallization kinetics results show that the addition of MMT facilitated the crystallization of nylon 10,10 as a heterophase nucleating agent; however, when the content of MMT was high, the physical hindrance of MMT layers to the motion of nylon 10,10 chains retarded the crystallization of nylon 10,10, which was also confirmed by polarized optical microscopy. However, both nylon 10,10 and nylon 10,10–MMT nanocomposites exhibited multiple melting behavior under isothermal and nonisothermal crystallization conditions. The temperature of the lower melting peak (peak I) was independent of MMT content and almost remained constant; however, the temperature of the highest melting peak (peak II) decreased with increasing MMT content due to the physical hindrance of MMT layers to the motion of nylon 10,10 chains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2181–2188, 2003     

Structure‐property relationships in commercial polyetheretherketone resins

Key relationships between molecular structure and final properties are reported for standard flow and high flow grades of commercially‐available polyetheretherketone (PEEK) resins that differ primarily in molecular weight and molecular weight distribution. Despite similar chemistry and composition, the molecular size‐dependent structural differences associated with the PEEK resins in this study are shown to influence the crystallization rate, final crystallinity, and melt rheology during processing, which subsequently affects mechanical properties, including strength, ductility, and impact resistance. These structure‐property relationships provide fundamental understanding to aid in the design and manufacturing of industrial and medical devices that leverage both the advantages common to all PEEK resins, including chemical and thermal resistance, mechanical strength, and biocompatibility, as well as more subtle differences in crystallization kinetics, melt rheology, ductility, and impact resistance. POLYM. ENG. SCI., 57:955–964, 2017. © 2016 Society of Plastics Engineers     

Structure–physical property relationships in peroxide-cured butadiene–styrene copolymers

Structure–physical property relationships in high-vinyl butadiene–styrene copolymers have been determined for samples cured with dicumyl peroxide under the same conditions. Three different structures, butadiene–styrene–butadiene (B–S–B) triblocks, butadiene–styrene (B–S) diblocks, and random butadiene–styrene copolymers, have been examined. Flexural modulus increases with increasing styrene content owing to the inherent stiffness of a polystyrene backbone. Swelling increases whereas hardness and heat distortion temperature decrease with increasing styrene content. This behavior is explained by the decrease in crosslink density with increasing styrene content in all structures. Heat distortion temperatures of the B–S–B and B–S networks are superior to the heat distortion properties of the random structures. The B–S–B structure is the most solvent resistant, followed by the random copolymers, with the B–S structures swelling to the greatest extent. Swelling differences between the B–S–B and random networks decrease with increasing styrene content, while swelling differences between the B–S–B and B–S networks increase with increasing styrene content. These results are explained by the nature of the crosslinking reaction and the number of loose ends present in each network.     

Structure–property relationships in thermoplastic‐apparent interpenetrating polymer networks based on crystallizable polyurethane and styrene–acrylic acid copolymer

Structure–property relationships in thermoplastic‐apparent interpenetrating polymer networks (t‐AIPNs), prepared by mechanical blending in a common solvent of crystallizable polyurethane (CPU) and styrene/acrylic acid random copolymer (S/AA), were investigated by means of wide‐angle and small‐angle X‐ray scattering (WAXS and SAXS), dynamic mechanical analysis (DMA), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and density, water uptake, deformation, and strength characteristics measurements. Several mechanical and dielectric relaxations of the pure components were characterized, and the effects thereupon induced by blending were followed. The two components show weak affinity to each other. The t‐AIPNs can be classified into two groups with high and low contents of CPU, showing essentially the behavior of CPU and of S/AA, respectively. On the other hand, deviations from additivity in several properties indicate interactions between the two components, caused by the formation of H‐bonds between their functional groups, and resulting in partial miscibility. In addition, significant changes are observed on some properties of the t‐AIPNs on addition of small amounts of either of the components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 385–397, 1999     

Structure–microhardness correlation in blends of nylon 6/nylon 66 monofilaments

The microstructure (crystallinity, long spacing) and the micromechanical properties (microhardness H) of two series of nylon 6 and nylon 66 monofilaments and their blends were investigated as a function of annealing temperature T_A and uniaxial deformation in a wide composition range. In case of the homopolymers, the gradual rise of microhardness with T_A is interpreted in the light of the increasing values of the crystallinity α and the hardness of the crystals H_c. The depression of the hardness values of the blends from the additive behavior of the hardness of individual components is discussed in the basis of the crystallinity depression of one component by the second one and viceversa. Finally, the influence of drawing and pressing the blends at 130°C which leads to a hardness increase is also explained in the light of an increase in the H_c value of nylon 66 due to orientation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 636–643, 2000     

Structure–properties relationships in clay nanocomposites based on PVDF/(ethylene–vinyl acetate) copolymer blends

The relationships between the microscopic structure and the macroscopic properties in two sets of clay nanocomposites based on polymer blends comprised of poly(vinylidene fluoride) (PVDF) and ethylene–vinyl acetate copolymer (EVAc) were examined. In nanocomposites based on a polymer blend matrix with high content of polar groups (VAc) the dispersion of polar nanoclay leads to significant enhancement in toughness and a substantial increase in viscosity. However, in nanocomposite blends based on a less polar matrix (i.e. with fewer VAc groups) it is the hydrophobic organoclay that leads to higher modulus and stronger viscoelasticity. The dispersion of nanoparticles and the mechanical response are discussed in terms of emulsifying efficiency of the clay particles in the immiscible polymer blend, an effect that largely depends on the localized interactions between the polymer groups and the clay surface modifier. The potential of nanoclays to serve as matrix sensitive structure-directing agents in tailor-made materials is demonstrated.     

Structure–property relationships of thermally bonded polypropylene nonwovens

The effect of fiber structure and morphology on the resultant mechanical and low load deformation properties of thermally bonded nonwoven polypropylene fabrics has been studied. Commercially available staple polypropylene fibers varying in linear density and draw ratio (Herculon and Marvess staple fibers) were used in this study. The orientation of these fibers was characterized by birefrigence measurements. Differential scanning calorimetry measurements were made to determine the heat of fusion and melting point of fibers. Experiments confirm that tensile strength and stiffness of the fabrics correlate with this fiber structure. Under the same bonding conditions fabrics made from fibers with low draw ratios show higher tensile strength and stiffness than do fibers with high draw ratios. The mechanical properties of fabrics were found to be greatly affected by the thermal bonding temperature. The tenacity and flexural rigidity of fabrics made from poorly oriented fibers show higher values than those made from highly oriented fibers. The shrinkage of the fabrics was observed to increase with increasing bonding temperature in both machine and cross machine directions. The changes in fabric thickness due to the thermal bonding are considerably lower for poorly oriented fibers.     

Structure–property relationships in bibenzoxazole polymers containing fluorocarbon linkages

A series of bibenzoxazole polymers with general formula where R′f and Rf are fluorocarbon-containing linkages has presented a unique opportunity to determine relationships between physical transitions and molecular structure. The results of oscillatory thermomechanical experiments (～1 Hz) show two glassy-state and a glass transition as amorphous transitions for each material above ?180°C. Each glassy-state transition is correlated with onset of motion of specific linkages, the flexibilities of which depend on the structure and molecular positions of the linkages. The glass transition temperatures depend on the two relaxations (T < T_g) in a systematic manner.     

Reprocessing acrylonitrile–butadiene–styrene plastics: Structure–property relationships

Acrylonitrile–butadiene–styrene (ABS) plastics from computer equipment housings have been reprocessed, some under various conditions of temperatures and shearing rates and others for multiple numbers of cycles. Structural changes in these reprocessed materials were investigated by infrared spectroscopy (FTIR), gel permeation chromatography, and dynamic mechanical thermal analysis. Gas chromatography/mass spectrometry was used to analyze extracts from the ABS plastics. These studies were related to measurements of the mechanical properties of the reprocessed materials, and the fracture surfaces were examined using scanning electron microscopy. It was found that impact strength was much more significantly affected than tensile properties by reprocessing. Within the range of reprocessing parameters studied, temperature had a more significant effect than shear rate on mechanical properties. Significant reductions in impact strength and slight increases in stiffness and strength, particularly following reprocessing at the highest temperature of 270°C and multiple reprocessing, were linked to loss of small molecules (including lubricants), degradation (crosslinking and scission) of the rubber phase, and changes in the morphology seen in the fracture surfaces. POLYM. ENG. SCI., 47:120–130, 2007. © 2007 Society of Plastics Engineers     

Structure–property relationships in thermally aged cellulose fibers and paper

The research presented in this paper investigates the effect of thermally accelerated aging on the submicrostructure of cellulose and attempts to relate such changes to the well‐documented loss of mechanical strength in aged paper. Filter paper and ramie fibers samples were aged in vacuo at 160°C. Small angle X‐ray scattering (SAXS) was used to study void structure within the fibers and hydration used as a structural probe. On hydration, the void radius of gyration and area decrease, while the void aspect ratio and overall void fraction increase. After aging, the wet structure more closely resembles the dry, suggesting that water cannot expand the structure to the same extent. It is postulated that increases in local ordering on aging create a structure more resistant to disruption by water. The use of additional techniques, namely Fourier transform IR spectroscopy, wide angle X‐ray scattering, scanning electron microscopy (SEM), environmental SEM, and measurement of water retention value, provided additional indirect support for the postulated model. There is no direct evidence for significant crystallinity changes in aged material, suggesting that if structural rearrangements occur, they will be local in nature. There is also no evidence for the formation of covalent crosslinks or new chemical species on aging. Water retention values and wet SAXS results concur, highlighting the importance of water in the cellulose structure and the reduced capacity for water sorption in aged samples. SEM observations show that the failure mechanism in paper changes with age from fibers pull out (i.e., interfiber bond failure) to fiber failure, and wide and zero span tensile tests indicate a weakening of the fibers. These results are consistent with previous reports, and we attribute them primarily to chain scission, although the increased intrafiber bonding may have an influence on the values obtained. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1465–1477, 1999     

Comparison of nanocomposites based on nylon 6 and nylon 66

Nylon 6 and nylon 6,6 organoclay nanocomposites were prepared by melt processing using a twin screw extruder. The effects of polyamide type and processing temperature on the mechanical properties and the morphology of the nanocomposites were examined. Mechanical properties, transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), percentage crystallinity and isothermal thermo-gravimetric analysis (TGA) data are reported. A particle analysis was performed to quantitatively characterize the morphology; these results are later employed in modeling the modulus of these materials using composite theory. No significant difference was observed in the mechanical properties and morphology of PA-6 nanocomposites processed at two different temperatures. PA-6 nanocomposites had superior mechanical properties than those made from PA-66. The tensile strength of PA-66 nanocomposites deviated from linearity at high levels of MMT. WAXD and TEM results show that the PA-6 nanocomposites are better exfoliated than the PA-66 nanocomposites, which exhibit a mixture of intercalated and exfoliated structures. Mechanical properties were consistent with the morphology. DSC reveals a higher percentage of crystallinity in the PA-66 samples. Isothermal TGA shows only a 5% difference in the degradation of the organic modifier on the organoclay processed at 240 °C versus 270 °C. Particle analysis shows a higher average particle length and thickness, and a lower average particle density and aspect ratio in nanocomposites based on PA-66 versus PA-6. The Halpin-Tsai and Mori-Tanaka composite theories predict satisfactorily the behavior of the PA-6 nanocomposites, while the PA-66 nanocomposites were predicted acceptably up to a certain volume fraction where the non-linear behavior takes effect. All the results indicate that there is a lower degree of exfoliation in the nanocomposites produced with a PA-66 matrix apparently stemming from the chemical differences between PA-6 and PA-66.     

Structure–property relationships for azo disperse dyes on polyurethane fibre

Using two series of monoazo disperse dyes, the relationships between the molecular structure of dye and its dyeing properties, such as adsorption behaviour, fastness properties and distribution on polyurethane–polyester blends, were thoroughly investigated. Correlation analysis of experiment data revealed that the partition coefficient between octanol and water (CLogP) is the main factor affecting dye sorption. A greater level of CLogP tends to have a greater isotherm coefficient and better rubbing and washing fastness on polyurethane fibre, as well as a greater distribution ratio between the components of the blend. The dye dipole moment is negatively correlated with various degrees of washing fastness. The dye with two terminal hydroxy groups exhibited notable sorption on the polyurethane component and has the largest partition ratio on polyurethane–polyester in the blend. Corresponding regression analysis equations were identified.     

Effect of sodium montmorillonite source on nylon 6/clay nanocomposites

The effect of sodium montmorillonite source on the morphology and properties of nylon 6 nanocomposites was examined using equivalent experimental conditions. Sodium montmorillonite samples acquired from two well-known mines, Yamagata, Japan, and Wyoming, USA, were ion exchanged with the same alkyl ammonium chloride compound. The resulting organoclays were extruded with a high molecular weight grade of nylon 6 under the same processing conditions. Quantitative analysis of TEM photomicrographs of the two nanocomposites reveal a slightly larger average particle length and a slightly higher degree of platelet exfoliation for the Yamagata based nanocomposite than the Wyoming version, thus, translating into a higher particle aspect ratio. The stress-strain behavior of the nanocomposites appears to reflect the nanocomposite morphology, in that higher stiffness and strengths are attainable with the increased particle aspect ratio. Moreover, the trends in stiffness behavior between the two types of nanocomposites may be explained by conventional composite theory.     

Structure–property relationships for liquid transport in modified polypropylene membranes

In view of the intensifying interest in the application of polymeric membranes in mixture separation processes, the permeation and permselective properties of polypropylene films toward several candidate organic liquids and vapors were investigated. Polymer films were subjected to solvent and thermal treatments, and the effects of these treatments on film morphology and transport properties were studied. Structure–property relationships for membrane permeation were then developed. Polypropylene films were found to be selective toward toluene, relative to isooctane, and p-xylene relative to o-xylene. Liquid flux rates were found to depend primarily upon the solubility of the permeants in the films and the absolute difference in the solubility parameters of the polymer–liquid pair provided a good basis for correlation of this effect. Considering liquids of closely similar solubility parameters, fluxes were found to be dependent upon the apparent molecular cross sections of the permeants. Films annealed in various organic solvents at temperatures of 60–100°C exhibited enhanced permeability, with up to fifteenfold increase relative to untreated membranes, but with reduced selectivity towards the permeants. A mechanism to account for these effects through consideration of the influence of treating solvent type on polymer morphology is proposed. It postulates the formation of more open or coarser spherulitic structures as a result of recrystallization in the presence of solvent during annealing. The enhanced flux rates in the treated films are attributed to the changes in the spherulite textures and to diminished intercrystalline tie chain constrainment within the spherulitic substructure.     

Structure–property relationships in some composite systems. Deformation mechanism

In the present paper, we report the photoelastic behavior of composite elastomeric systems. The samples were obtained by vulcanizing mixtures of cis-polybutadiene and a polar monomer. The polar monomer used was methacrylic acid or magnesium methacrylate. The photoelastic analysis was carried out on samples with different monomer amount and in different swelling conditions. This kind of analysis gives informations about the deformation mechanism of these systems.