Modulus Peak Research Articles

Preparation and characterization of boron-nitrogencoordination phenol resin/SiO2 nanocomposites

The boron-nitrogen-containing phenol-formaldehyde resin (BNPFR)/SiO2 nanocomposites (BNPFR/SiO2) were synthesized in-situ, and structure of BNPFR/SiO2 nanocomposites was characterized by FTIR, XRD and TEM. The loss modulus peak temperature Tp of BNPFR/SiO2 nanocomposites cured with different nano-SiO2 content are determined by torsional braid analysis (TBA). The thermal degradation kinetics was investigated by thermogravimetric analysis (TGA). The results show that nano-SiO2 particulate with about 50 nm diameter has a more uniformly distribution in the samples. The loss modulus peak temperature Tp of BNPFR/SiO2 nanocomposite is 214 oC when nano-SiO2 content is 6 wt%. The start thermal degradation temperature Tdi is higher about 30 oC than pure BNPFR. The residual rate (%) of nanocomposites at 800 oC is above 40 % when nano-SiO2 content is 9 %. The thermal degradation process is multistage decomposition and following first order.

Preparation and characterization of boron-nitrogen coordination phenol resin/SiO2nanocomposites

The boron-nitrogen-containing phenol-formaldehyde resin (BNPFR)/<TEX>$SiO_2$</TEX> nanocomposites (BNPFR/<TEX>$SiO_2$</TEX>) were synthesized in-situ, and structure of BNPFR/<TEX>$SiO_2$</TEX> nanocomposites was characterized by FTIR, XRD and TEM. The loss modulus peak temperature <TEX>$T_p$</TEX> of BNPFR/<TEX>$SiO_2$</TEX> nanocomposites cured with different nano-<TEX>$SiO_2$</TEX> content are determined by torsional braid analysis (TBA). The thermal degradation kinetics was investigated by thermogravimetric analysis (TGA). The results show that nano-<TEX>$SiO_2$</TEX> particulate with about 50 nm diameter has a more uniformly distribution in the samples. The loss modulus peak temperature <TEX>$T_p$</TEX> of BNPFR/<TEX>$SiO_2$</TEX> nanocomposite is <TEX>$214^{\circ}C$</TEX> when nano-<TEX>$SiO_2$</TEX> content is 6 wt%. The start thermal degradation temperature <TEX>$T_{di}$</TEX> is higher about <TEX>$30^{\circ}C$</TEX> than pure BNPFR. The residual rate (%) of nanocomposites at <TEX>$800^{\circ}C$</TEX> is above 40 % when nano-<TEX>$SiO_2$</TEX> content is 9 %. The thermal degradation process is multistage decomposition and following first order.

Effects of ultrasound on glass transition temperature of freeze-dried pear (Pyrus pyrifolia) using DMA thermal analysis

The effect of ultrasound pretreatment at various power (360W, 600W and 960W, frequency 20kHz) on the glass transition temperature of freeze dried pear (Pyrus pyrifolia) has been studied. DMA temperature plots were divided into four sections (A – glassy region, B – transition region, C – Rubbery plateau region and D – terminal region) with the aim to analyze their properties changed with sonication. Under the same freeze drying condition, with the increase in ultrasonic power, dried pear showed higher glass transition in terms of storage modulus, loss modulus and loss tangent peak. Also a decrease in aw (0.31–0.23) and in moisture content (0.12–0.08g/gd.b.) has been observed. Samples pretreated with ultrasound showed a better texture profile and much porous structure compared to control one. The results from the study indicated that, ultrasound pretreatment prior to freeze drying can improve the stability during storage of freeze dried pear.

A universal route towards thermoplastic lignin composites with improved mechanical properties

Nanocomposites based on synthetic polymers grafted from kraft lignin with average particle size of 5 nm were synthesized using atom transfer radical polymerization (ATRP). Lignin macroinitiators were prepared, and polystyrene and poly(methyl methacrylate) were polymerized with target degree of polymerization of 450 resulting in materials having lignin mass fractions of 4.5%, 8.3%, and 22.1% for the poly(methyl methacrylate) samples and 3.2%, 7.1%, and 19.6% for the polystyrene samples. Tensile testing showed a decreased modulus but enhanced toughness of all nanocomposites compared to homopolymers, and the poly(methyl methacrylate)-grafted samples had nearly twice the ultimate elongation as the polystyrene grafts at high graft density. Both types of grafted nanocomposites had toughness values that were greater than 10-times that of the corresponding kraft-lignin/polymer blend system, indicating the potential of ATRP as the basis for the ‘one component’ composite approach towards more sustainable polymeric materials. Dynamical mechanical analysis was used to measure softening temperatures, and both the polystyrene-grafted and poly(methyl methacrylate)-grafted nanocomposites had a peak in the loss modulus that was higher than the corresponding homopolymer, consistent with strong polymer–lignin interactions. Lignin grafted with thermoplastic polymers could be an important material based on an inexpensive, renewable feedstock that offers unique mechanical properties compared with many other nanocomposites based on inorganic nanoparticles. Our results indicate that ATRP is well suited for preparing lignin-based thermoplastics and could be the basis for hybrid materials that make effective use of this important renewable resource.

Influence of Poly(Vinyl Butyral) on the Dynamic-Mechanical and Mechanical Properties of Polypropylene/Wood Flour Composites

This study reports the influence of recycled poly (vinyl butyral) (PVB) in dynamic mechanical and mechanical properties of polypropylene (PP)/wood flour composites prepared in a twin screw extruder. After extrusion, the PP/wood flour composites were injection molded to obtain specimens for tensile, flexural, impact and dynamic mechanical (DMA) tests. The morphology of the composites was analyzed by scanning electron microscopy (SEM). The addition 10 wt% of PVB in PP/wood flour composite reduced from 5°C to-10°C the β transition (glass transition) peak temperature of the loss modulus. In a temperature range between 40°C and 100°C the composites containing PVB presented the highest peak in the loss modulus. The most intense tan delta peaks between 50°C and 100°C for composites containing PVB were attributed to the combined effects of PP α transition with the PVB glass transition temperature. The PP/wood flour composites with PVB presented a tendency to increase the absorbed energy by impact.

The proper glass transition temperature of amorphous polymers on dynamic mechanical spectra

Glass transition is crucial to the thermal and dynamical properties of polymers. Thus, it is important to detect glass transition temperature (T g) with a sensitive and proper method. Dynamic mechanical analysis (DMA) is one of the most frequently used methods to determine T g due to its advantage of high sensibility. However, there is controversy in the past literatures to determine the proper glass transition temperature among three transition temperatures, i.e., T g1, T g2 and T g3 in the dynamic mechanical spectra, which correspond to the temperature abscissa of intersect value of two tangent lines on storage modulus (E′), the peak of the loss modulus (E″) and the peak of the loss tangent (tan δ). In this work, these three transition temperatures were compared with the glass transition temperature determined by DSC (T gDSC). Based on the discussion of different modes of molecular motion around the glass transition region, it is demonstrated that T g1 and T g2 have the same molecular mechanism as T gDSC, i.e., local segmental motion which is enthalpic in nature and determines the proper glass transition temperature, while T g3 is assigned to the transition temperature of entropic Rouse modes, thus cannot be used as the proper glass transition temperature.

Thermomechanical Properties of KevlarTM Reinforced Benzoxazine-Urethane Alloys

Ballistic armor is one of an important application which required high performance of fiber-reinforced polymer due to its outstanding specific mechanical properties. Therefore, KevlarTM reinforced benzoxazine-urethane alloys as ballistic impact resistance composites were developed in this research. The polybenzoxazine alloy composites were fabricated by compression molding at 200ºC and 5 MPa by a compression molder. The amount of urethane fraction in the alloy matrix was ranging from 0-40wt% while the fiber content was kept constant at 80wt%. The mechanical properties of the matrix alloys and their KevlarTM fiber composites were characterized by dynamic mechanical analysis and universal testing machine. The results revealed that storage modulus at room temperature of the composites was reduced from 16.82 GPa when using the neat polybenzoxazine as a matrix to the value of 11.89 GPa at 40wt% of urethane content in the alloy matrix. Moreover, the more urethane in the alloy matrix resulted in lower flexural modulus of the KevlarTM composites i.e. 22 GPa when using the neat polybenzoxazine as a matrix to the value of 12 GPa when using 40wt% of urethane in the alloy matrix. Interestingly, glass transition temperature (Tg) obtained from the maximum peak of the loss modulus was observed to be in the range of 187-247ºC, which was significantly higher than those of the two parent polymers. Furthermore, the activation energy of the alloys was found to increase with increasing urethane content, which corresponded to the observed Tg value enhancement. The observed synergism in Tg of KevlarTM reinforced benzoxazine-urethane was an outstanding characteristic for a wide range of applications, which requires high thermal stability.

Viscoelasticity and microstructure of a hierarchical soft composite based on nano-cellulose and κ-carrageenan

Soft composites consisting of kappa-carrageenan gel interspersed with nano-cellulose were produced mimicking soft material structures. Microfibrillar cellulose (MFC) with a broad distribution of nano-fibre lengths was used as well as nano-crystalline cellulose (NCC) consisting of 20-nm nano-rods. The nano-fibre concentration, as well as the potassium ion concentration, was varied. The composites were characterized by rheology and light and electron microscopy. The incorporation of NCC into the carrageenan gel led to significant stiffening, and a sharp peak in the storage modulus occurred during gelation. This peak was not observed with MFC, which produced softer composites. An increase in the potassium concentration generally led to a more aggregated carrageenan structure with coarser network strands and increased modulus. By choosing suitable amount of nano-fibres and potassium concentration, soft composites with tailored properties could be produced.

Rheology and synergy of κ-carrageenan/locust bean gum/konjac glucomannan gels

The rheology and melting of mixed polysaccharide gels containing konjac glucomannan (KGM), locust bean gum (LBG) and κ-carrageenan (KC) were studied. Synergy-type peaks in the Young's modulus at optimal mixing ratios were found for both KC/LBG and KC/KGM binary gels at a fixed total polysaccharide content (1:5.5 for LBG:KC and 1:7 for KGM:KC). The Young's modulus peak for KC/KGM was higher than for KC/LBG gels. The same stoichiometric mixing ratios were found when either LBG or KGM was added to KC at a fixed KC concentration, where the Young's modulus increased up to additions at the stoichiometric ratio, but leveled off at higher LBG or KGM additions. Addition of KGM or LBG to the 2-component gels beyond the stoichiometric (optimal) mixing ratio at a fixed total polysaccharide content led to a decrease in the Young's modulus and an increase in the rupture strain and stress in extension, and both trends were stronger for KGM than for LBG.Differential scanning calorimetry of the gels revealed the development of a second melting peak for the KC/KGM gels that increased with KGM addition up to higher KGM contents than the stoichiometric ratio. For the KC/LBG gels, only a slight broadening and shift to a higher temperature were observed. When the three polysaccharides were mixed, the DSC endotherms reflected only the main features of the interaction between KC and KGM, and the same was true for the fracture in extension. The different trends led to higher Young's moduli at intermediate KC concentrations when a 1:1 addition of LBG:KGM was used than when either only KGM or LBG was added at a fixed total polysaccharide concentration. This suggests that no special interactions arise when the three polysaccharides are mixed and the binding mechanisms are simply a sum of the bindings observed for KC/KGM and KC/LBG two-component gels.

Laboratory Testing of Paving Mixes-Dynamic Material Functions and Wheel Tracking Tests

Five asphalt paving mixes prepared with different asphalt binders (one conventional, two oxidized, and two modified by styrene-butadien-styrene copolymer, 2% and 4% by weight) were studied in small amplitude oscillation and wheel tracking tests. The main focus of the study was to investigate these materials at a relatively high service temperature (58°C). From dynamic testing at temperatures ranging from -10°C to 80°C, the master curves of dynamic material functions (storage modulus, loss modulus, and loss tangent) were prepared at a reference temperature of 58°C. The relaxation and retardation spectra were calculated for all the materials, and the corresponding (compressive) compliance, D(t) (linear viscoelastic), was also determined from the retardation spectrum. It was shown that D(t) can be effectively approximated from the magnitude of the complex compliance by transforming the domain of the reduced frequencies to the time domain. From the wheel tracking test performed at 58°C, the accumulated compliance function (deformations larger than in the dynamic tests) was calculated and appended to the linear viscoelastic D(t). A simple model of the compounded compliance with stretched time (developed earlier) was used. It was shown that, in most of the tested materials, the information from the dynamic testing seemed to be poorly correlated with the trend of the compliance obtained from the wheel tracking data when the compounded compliance was plotted. On the other hand, when the model of compliance was fitted only to a subset of the linear viscoelastic data (the subset generated by points defining the peak of the loss tensile modulus), the accumulated compliance from the wheel tracking test can be estimated by the same model.

Role of interparticle attraction in the yielding response of microgel suspensions

We use rheological measurements to examine the yielding behavior of a microgel system spanning the range from soft jammed glassy suspensions dominated by inter-particle repulsion to colloidal gels produced by attractive interactions. Under repulsive conditions, the suspensions display a prototypical soft glassy yielding response in which the shear loss modulus exhibits a single peak on increasing strain during the crossover from elastic to viscous behavior. By contrast, under fully attractive conditions the colloidal gel displays a more complex yielding, with two distinct peaks in the loss modulus in the vicinity of the yield strain. It is apparent that the gels yield initially by network rupture, followed by shear induced densification which leads to the formation of compact clusters. We show that the second peak in the loss modulus is consistent with the subsequent breakup of these dense clusters. We quantitatively map the steady progression from simple glassy yielding to the more complex gel response on increasing attraction strength by the evolution of peak locations, magnitudes and frequency dependencies. Notably, the peak locations diverge as the network becomes more fragile and spatially heterogeneous with increasing attraction strength. There is little frequency dependence in the peak positions, but the amplitude of the second yielding peak shows a non-monotonic dependence with a maximum near 5 rad s−1. Time-resolved measurements and decreasing strain sweeps highlight pronounced differences in the reversibility of the network rupture and cluster breakup processes. Correspondingly, the linear viscoelastic properties of the gel are strongly dependent on mechanical history whereas the glass exhibits no such dependence.

Interfacial toughening and consequent improvement in fracture toughness of carbon fiber reinforced epoxy resin composites: induced by diblock copolymers

Carbon fibers chemically grafted with hydroxyl-terminated diblock copolymer poly (n-butylacrylate)-b-poly (glycidyl methacrylate) (OH-PnBA-b-PGMA), were used as the reinforcement for epoxy composites. The multi-filament composite specimens were prepared and measured by dynamic mechanical analysis (DMA), to study the interfacial tough- ness of carbon fiber reinforced epoxy composites with the diblock copolymers. The loss modulus and loss factor peaks of !-relaxation indicated that composites with diblock copolymers could dissipate more energy at small strain and possess bet- ter interfacial toughness, whereas composites without the ductile block PnBA having the worse interfacial toughness. The glass transition temperature and the apparent activation energy calculated from the glass transition showed that the strong interfacial adhesion existed in the composites with diblock copolymers, corresponding with the value of interfacial shear strength. Therefore, a strengthening and toughening interfacial structure in carbon fiber/epoxy composites was achieved by introducing the diblock copolymer OH-PnBA-b-PGMA. The resulting impact toughness, characterized with an Izod impact tester, was better than that of composite without the ductile block PnBA.

Comparative Study on Degradation, Aggregation and Rheological Properties of Actomyosin from Cold, Temperate and Warm Water Fish Species

Proteolytic degradation and thermal aggregation patterns and dynamic rheological properties of actomyosin prepared from Alaska pollock (Theragra chalcogramma), Pacific whiting (Merluccius productus), bigeye snapper (Priacanthus spp.), lizardfish (Saurida spp.) and threadfin bream (Nemipterus spp.) surimi were comparatively studied. There was a significant endogenous protease activity observed in crude actomyosin samples where Pacific whiting and lizardfish exhibited the highest proteolytic activity. SDS-PAGE analysis showed that intensity of myosin heavy chain bands of Pacific whiting, bigeye snapper, lizardfish and threadfin bream decreased with extended incubation time, resulting in medium and low molecular weight proteins. For all tested fish species, a 0.5°C min heating rate resulted in higher turbidity values followed by 1.0°C min and then 2.0°C min. Temperature onset point for turbidity increase was significantly affected by species. Storage modulus peak temperatures, obtained from temperature sweep tests of actomyosins, were similar to thermal transition values obtained from differential scanning calorimetry, indicating that peaks obtained from the dynamic tests were related to protein denaturation temperatures. Slower heating rate shifted the thermal transition temperature to a lower value. These observations should give better understanding of the thermal sensitivity of fish species with regards to gelation properties and proteolytic degradation.

Yielding and flow of concentrated Pickering emulsions

We have used rheo-imaging to investigate the shear flow of particle-stabilized (Pickering) emulsions with different interactions between droplets. To minimize creaming, we have worked with arrested networks of droplets. We observe three different yielding mechanisms as well as shear thickening at high strain. Pickering emulsions comprised of repulsive droplets respond to small strains initially by reversible movement, then, as the strain is increased, yielding occurs via cage breaking. At large strains there is a peak in both moduli and correlations between droplet trajectories indicative of shear thickening and jamming. Pickering emulsions comprised of attractive droplets share similar features and additionally have a loss modulus peak at low strain associated with the breakage and rearrangement of the attractive bonds. We observe that small attractive droplets already start to move irreversibly at small strains even though yielding has not yet occurred. As the strain is increased, the percolating network of larger droplets is eventually completely broken and the sample yields as a whole. Finally, we explore what happens when a highly compressed emulsion or bi-liquid foam is subjected to shear flow: we find that at high strain the particles fail to stabilize the interface and the emulsion is destroyed.

Structure-Property Correlation of Composites Impregnated with Aspartimide Oligomer

Carbon fiber and glass fiber composites impregnated with aspartimide oligomer were fabricated and their structure-property correlation was studied. Experimental results reveal that with increasing chain length of aspartimide oligomer, mechanical properties of composites increase, but thermal properties decrease. With decreasing chain length, storage modulus and loss tan delta peak temperature of composite increase as a consequence of increased rigidity of matrix polymer resin resulted from crosslink density increase, concurrently, loss modulus and tan delta value of composites undergo a decrease.

Dielectric and electric properties of plasticized PEO‐AgCF3SO3‐SiO2 nanocomposite polymer electrolyte system

AbstractThe effect of plasticizer poly(ethylene glycol) (PEG) on dielectric and electrical properties of an ionically conducting polymer nanocomposite electrolyte PEO: AgCF3SO3: SiO2: PEG has been investigated. The variation of relative dielectric constant and tangent loss peak with frequency have been discussed. The ionic and polymer segmental motions have been analyzed by electrical modulus and dielectric permittivity. The electrical modulus formalism is used to study the ionic relaxation process in these composites in terms of conductivity relaxation time. On addition of plasticizer, the modulus peak shifts toward higher frequency side suggesting the speeding up of the relaxation time. The frequency dependence of AC conductivity follows the universal power law. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Stress concentration in carbon fiber revealed by the quantitative analysis of X-ray crystallite modulus and Raman peak shift evaluated for the variously-treated monofilaments under constant tensile forces

The stress distribution at the various parts of PAN-based carbon fiber (CF) monofilament has been estimated using a complex mechanical model on the basis of the quantitative evaluation of crystallite modulus through the micro-beam wide-angle X-ray diffraction measurement under tension as well as the micro-Raman spectral measurement under tension. When a CF monofilament was tensioned along the fiber axis, the outer-surface part of nanometer-order depth was found to owe a tensile stress about 1.5 times higher than the inner-surface and core parts, indicating an easier start of fiber breakage from the outer surface part. This knowledge gives us an important hint to the development of mechanically-tough carbon fiber without any such local stress concentration on the outer surface part.

A novel acrylamide-anatase hybrid nanocomposite

A novel hybrid-nanocomposite of polyacrylamide-TiO2 (PAM/TiO2) with nano-anatase particles was synthesized in two steps. Firstly, the surface of nano-anatase particles was modified by 3-methacryloxy-propyl-trimethoxysilane (TMSM) as coupling agent by sol–gel method. Secondly, the surface modified nano-anatase particles were grafted onto the acrylamide monomer (AM) as an organic phase by free radical polymerization. The spectral (Fourier transform Infrared spectroscopy) and thermal (TGA) methods, verified the participation of coupling agent, polymer and titanium dioxide (anatase) into the hybrid structure. The results also showed that the degradation temperatures and residual content were obviously higher in nanocomposite than those of pure polyacrylamide (PAM). Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies proved that the nano-anatase particles have been uniformly encapsulated inside the nanocomposite sample containing 5wt% TiO2. However, the agglomeration of nano-particles in the nanocomposite with 20wt% of TiO2 was detected by atomic force microscopy (AFM) and dynamic mechanical thermal analysis (DMTA) studies. Thermo-mechanical properties of acrylamide homopolymer (PAM) and their nanocomposites were investigated by DMTA. The shifts in storage modulus and tanδ peaks were attributed to morphological changes in the nanocomposites with increasing the amount of inorganic nano-particles and their distribution in polymer matrix. Flocculation behavior of PAM and PAM/TiO2 in two different level of titanates (i.e. 5 and 20wt% TiO2) for 0.25wt% nano-clay suspension was evaluated using batch method. The adsorption results showed that PAM/TiO2 have ability for interaction with clay particles by means of adsorption through electrostatic interaction, Vander Waals forces and hydrogen bonding. However, it was found that the flocculation efficiency of the pure polymer (PAM) and the hybrid-nanocomposite (5wt% TiO2) is much better than that of its high concentration (20wt% TiO2) in the hybrid. This flocculation behavior can be attributed to uniform distribution of nano-particles and agglomeration possibility in the case of low and high concentration level of titanate in hybrid nanocomposite, respectively.

Functional graded scaffold of HDPE/HA prepared by selective laser sintering: microstructure and mechanical properties

This paper presents a study on the effect of hydroxyapatite (HA) content on the microstructure and mechanical properties of high-density polyethylene (HDPE)/HA composites and the fabrication of functional graded scaffold of HDPE/HA by selective laser sintering (SLS). The microstructure of the sintered composite scaffolds had interconnected pores with diameters of 30–180 μm and porosity of 45–48 %. The HDPE/HA composite scaffolds had a flexural modulus of 36–161 MPa and ultimate strength of 4.5–33 MPa. The maximum loss modulus peak tended toward lower temperature values for HDPE/HA composites with 10 and 20 % of HA content, indicating that the αχ relaxation was slightly affected by higher quantities of HA. The HA particles reinforced the matrix and minimized the plastic and definitive deformation under the test conditions. HDPE/HA functional graded scaffold fabricated using SLS with controlled microstructure and properties showed considerable potential for biomedical applications, being suitable for bone and cartilage tissue engineering.

Immersion mode material pocket dynamic mechanical analysis (IMP-DMA): A novel tool to study gelatinisation of purified starches and starch-containing plant materials

There is a clear need for improved methods for the study of the physical changes that occur in slurries and sol–gel systems that have significant water content. In this paper a novel immersion mode material pocket form of dynamic mechanical analysis (IMP-DMA) has been designed, combining material pocket technology to provide physical support to a powdered sample within an immersion bath. IMP-DMA allows the mechanical response of a powder during heating to be monitored in excess water. IMP-DMA was evaluated using a range of starch samples loaded as a slurry into a solid steel pocket, the mechanical responses of these samples were monitored as a function of temperature, and values for modulus and tanδ peaks were found to correspond well with events occurring at both the onset and peak gelatinisation temperatures as measured by differential scanning calorimetry (DSC) (e.g. wheat starch has an onset and peak DSC temperature of 49.3°C and 57.2°C, respectively, and shows a peak in tanδ at 52.8°C and a modulus peak at 57.7°C). Some limitations were found in the ability of DMA to detect transitions in starches with low or high amylose contents. IMP-DMA was shown to be an effective tool for monitoring the changes in starch structure that occur during gelatinisation, both in purified starches and in more complex starch-containing food materials. Thus, a new hyphenated form of DMA is now available that permits the thermally induced transitions of particle water dispersions to be characterised.