Lower Flexural Modulus Research Articles

Modified recycled tire fibers by gamma radiation and their use on the improvement of polymer concrete

While polymer cement concrete is a very versatile material with respect to its functions and economy, it has several disadvantages: high porosity, low flexural modulus and poor resistance to corrosive chemical reagents. Potential improvements include addition of recycled fibers. However, information on effects of fibers is insufficient, and less is known on effects of gamma irradiation on such concretes. In this work, concretes with polyester resin and silica sand were elaborated. Silica sand was partially replaced by recycled tire fibers (0.3, 0.6, 0.9 and 1.2 vol%) and gamma irradiation (50 and 100 kGy) was applied. Mechanical properties were determined in compression and flexion. Significant improvements on the mechanical properties were obtained and related to morphological and structural changes of the recycled tire fibers.

Mechanical and Physical Properties of Experimental Antifungal Denture Base Resins

Many denture wearers suffer from fungal infections, particularly Candida albicans, due to failure to properly clean or remove the prosthesis. These infections can cause denture stomatitis, which often leads to irritated or traumatized tissues. Current denture base materials do not have antifungal properties. We have recently synthesized several new antifungal compounds containing 1,4-diazabicyclo [2.2.2] octane (DABCO) (DC16NF, DC11MAF, C2-DC11MAF) that have shown significant antifungal properties.1 The purpose of this study is to incorporate these novel antifungal compounds and test mechanical and physical properties of the resulting antifungal materials. The Clotrimazole was also incorporated into denture acrylics and used as a positive control. Samples were then prepared into discs and bars. All groups were tested for flexural strength, flexural modulus, water sorption, and solubility. The results showed that all experimental groups exhibited similar flexural strength as the control, except DC16NF, which had significantly lower strength than the control. DC16NF and DC11MAF both exhibited significantly lower flexural modulus compared to the control while C2DC11MAF exhibited similar flexural modulus as the control. All experimental groups exhibited higher water sorption than the control and a similar or lower solubility as compared to the control. These results suggest that the new antifungal denture base materials possess similar mechanical and physical properties as commercial denture materials, although the formulations can be further optimized.

Microstructural and Mechanical Characterization of CAD/CAM Materials for Monolithic Dental Restorations.

To determine and compare the microstructure, flexural strength, flexural modulus, fracture strength, and microhardness of four types of computer-aided design/computer-aided manufacturing (CAD/CAM) materials for monolithic dental restorations. A lithium disilicate (LD; IPS e.max CAD), a zirconia-reinforced lithium silicate (ZLS; VITA Suprinity), a hybrid high-performance polymer (HPP) composite resin (GC Cerasmart), and a hybrid polymer-infiltrated ceramic network (PICN) material (VITA Enamic) were used to manufacture monolithic ceramic posterior crowns (n = 10) that were adhesively cemented on resin-based composite dies and loaded until fracture. In addition, 40 rectangular bars (n = 10) were milled and polished for three-point flexural strength testing. Microhardness (Vickers indentation), as well as quantitative (energy dispersive spectroscopy) and qualitative (scanning electron microscopy) structural analysis were conducted on fracture surfaces. Data were analyzed by one-way ANOVA and Tukey HSD post-hoc test (p = 0.05). Mechanical testing results showed that the material type has a significant effect on the fracture strength (p < 0.0001) of the monolithic crowns with ZLS and LD presenting significantly higher fracture strength than the PICN and HPP hybrid materials. LD showed the highest flexural strength (p < 0.0001) followed by ZLS, HPP, and PICN, respectively. The lowest flexural modulus and hardness were presented by HPP whereas ZLS had the highest flexural modulus and hardness. The LD presented the highest modulus of resilience and the PICN the lowest. All CAD/CAM crown materials exhibited high values of fracture and flexural resistance, making them suitable materials for posterior full-crown restorations. Glass-ceramics suffered more from catastrophic and nonreparable fracture patterns, whereas minimal chipping and type II fracture patterns were more common in hybrid materials. The combination of more flexibility, less stiffness, and increased softness with satisfactory flexural and fracture strength values observed in PICN and HPP makes these two hybrid materials suitable choices for chairside monolithic crown fabrication.

Enhanced mechanical properties of amorphous SiOC nanofibrous membrane through in situ embedding nanoparticles

AbstractFlexible ceramic nanofibers are highly desired due to their potential applications in free‐standing catalyst supports, fine particulate filters and flexible electronic devices. In this work, robust SiOC fibrous membranes composed of randomly oriented nanofibers with an average diameter of 550 nm were fabricated by a combination of electrospinning and post heat‐treatment process. The mechanical properties of the as‐prepared membranes were enhanced significantly through in situ embedding of palladium nanoparticles into the SiOC fibers. The optimized palladium‐doped SiOC fibrous membrane demonstrated a low flexural modulus of 7.79 kPa and a high tensile strength of 33.2 MPa. Reduced flaw size, initiation of nanocracks and pinning effect were proposed to explain the enhancement mechanism. Furthermore, the flexible SiOC membrane with excellent corrosion resistance exhibits a high filtration efficiency of 99.6% when the membrane weight is 4.8 g m−2, suggesting efficient filtration applications in harsh environments. This work also provides a feasible strategy for the design and fabrication of the flexible amorphous ceramic fiber membranes for various applications.

Preparation and Characterization of DGEBA/EPN Epoxy Blends with Improved Fracture Toughness

The physical and mechanical properties of blends composed of two kinds of epoxy resins of different numbers of functional groups and chemical structure were studied. One of the resins was a bifunctional epoxy resin based on diglycidyl ether of bisphenol A and the other resin was a multifunctional epoxy novolac resin. Attempt was made to establish a correlation between the structure and the final properties of cured epoxy samples. The blend samples containing high fraction of multifunctional epoxy resin showed higher solvent resistance and lower flexural modulus compared with the blends containing high fraction of bifunctional epoxy resin. The epoxy blends showed significantly higher ductility under bending test than the neat epoxy samples. The compressive modulus and strength increased with increasing of multifunctional epoxy in the samples, probably due to enhanced cross-link density and molecular weight. Morphological analysis revealed the presence of inhomogeneous sub-micrometer structures in all samples. The epoxy blends exhibited significantly higher fracture toughness (by 23% at most) compared with the neat samples. The improvement of the fracture toughness was attributed to the stick-slip mechanism for crack growth and activation of shear yielding and plastic deformation around the crack growth trajectories for samples with higher content of bifunctional epoxy resin as evidenced by fractography study.

Cellulose microcrystal improved interphase of ramie fiber‐reinforced epoxy resin composites

This article investigated the effect of cellulose microcrystal (CMC) and low molecular polyamide (PA650) on the mechanical and water absorption properties of ramie fiber‐reinforced epoxy composites. Results showed that coating mixture of CMC and PA650 (CMC/PA650) on the surface of ramie fiber improved the interfacial adhesion strength of ramie fiber/epoxy composites. As a result, the flexural strength, flexural modulus, and interlaminar shear strength of PA650/CMC‐coated ramie fabric‐reinforced epoxy composites (CPRFC) were 10.6%, 8.1%, and 7.4% higher than those of ramie fabric without coating reinforced epoxy composites (RFC). Additionally, saturated water absorption of CPRFC was reduced by 40.5% and 31.5% than that of RFC and PRFC, it seems that a water‐resistant interphase exists in the CPRFC and it is more efficient at the early stage of water immersion. However, without filling of CMC in PA650, lowest flexural modulus and highest flexural strain of the composites were found. POLYM. COMPOS., 39:E2207–E2216, 2018. © 2017 Society of Plastics Engineers

The residual monomer content and mechanical properties of CAD\CAM resins used in the fabrication of complete dentures as compared to heat cured resins.

BackgroundThe utilization of computer-assisted designing and computer-assisted milling CAD\\CAM resins in the fabrication of removable prostheses is a modern-day concept that offers many advantages over the use of the traditional polymethylmethacrylate (PMMA).AimThis study instigated some of the mechanical properties of CAD\\CAM denture base resin including the amount of residual monomer.MethodsThis study was conducted at the Faculty of Dentistry, King Abdulaziz University from October 2016 to February 2017. A total of seventy rectangular specimens were fabricated (group A: 35 heat-cured PMMA and group B: 35 CAD/CAM pre-polymerized acrylic resin blocks). The flexural strength and surface hardness were tested while the residual monomer content at baseline, two-day and seven-day intervals was estimated using gas chromatography (GC). Means and standard deviations were determined for each group as well as independent-samples t-test and ANOVA with repeated measures for comparison between the groups and subgroups of varying time intervals.ResultsHeat cured PMMA (A), displayed higher flexural strength and low value flexural modulus compared to CAD/CAM acrylic resin denture base material (B). Student t-test indicated highly significant differences (p<0.001) of the flexural strength (t=37.911) and flexural modulus (t=88.559). The surface hardness of group (B) was significantly higher compared to group (A) as indicated by the t-test (t=20.430). Higher release of the monomer content was detected by GC in group (A) at different time intervals with a statistically significant difference (p<0.001) in residual monomer content.ConclusionCAD/CAM resin may be considered suitable for use in the construction of denture bases.

Biocomposites reinforced with natural fibers:thermal, morphological and mechanical characterization

ABSTRACT This study evaluates the thermal, morphological and mechanical behavior of polypropylene (PP) composite with different natural fibers. The fibers used were wood, sugarcane, bamboo, babassu, coconut and kenaf with and without coupling agent. The thermal, morphological and mechanical properties were evaluated, and a composite PP+GFPP (glass fiber) was used as reference. The interaction at the interface fiber-polymer matrix was studied by scanning electron microscopy (SEM) at the fractured surface of the composites, as expected the presence of maleic anhydride (MA) as coupling agent increasedthe interaction at the interface. The influence of natural fiber in the degree of crystallinity of the composites was evaluated by DSC analysis. The samples of PP+GFPP and PP+(PP-MA)+WF (wood flour) showed better temperature stability. PP+GF also presented superior flexural modulus. The thermal dynamic mechanical behavior was evaluated by DMA, a decrease in storage modulus with increasing temperature was observed, the PP+GF and the composite containing maleic anhydride and sugarcane fiber showed higher modulus. The natural fiber biocomposites studied, consistently presented lower flexural modulus and tensile strength than the reference composite, with and without the use of coupling agent. As expected the use of natural fibers lowered the density compared to the reference material.

Mechanical properties: wood lumber versus plastic lumber and thermoplastic composites

Abstract Plastic lumber and thermoplastic composites are sold as alternatives to wood products. However, many technical standards and scientific studies state that the two materials cannot be considered to have the same structural behaviour and strength. Moreover, there are many compositions of thermoplastic-based products and plenty of wood species. How different are their mechanical properties? This study compares the modulus of elasticity and the flexural, compressive, tensile and shear strengths of such materials, as well as the materials' specific mechanical properties. It analyses the properties of wood from the coniferae and dicotyledon species and those of commercialized and experimental thermoplastic-based product formulations. The data were collected from books, scientific papers and manufacturers' websites and technical data sheets, and subsequently compiled and presented in Ashby plots and bar graphs. The high values of the compressive strength and specific compressive and tensile strengths perpendicular to the grain (width direction) shown by the experimental thermoplastic composites compared to wood reveal their great potential for use in compressed elements and in functions where components are compressed or tensioned perpendicularly to the grain. However, the low specific flexural modulus and high density of thermoplastic materials limit their usage in certain civil engineering and building applications.

Flexible Polyisocyanate Based Aerogels

ABSTRACTHighly flexible, durable aerogels with textile feel were developed at Aspen Aerogels Inc. by sol-gel chemistry and supercritical CO2 solvent extraction. These polyisocyanate-based aerogels reinforced with battings showed little to no brittle fracture with repeated flexing. The crosslinker, the isocyanate content and functionality played an important role on properties such as thermal conductivity, durability and flexural modulus at ambient and cryogenic temperatures. The polyisocyanate aerogels crosslinked with polyamine showed thermal conductivities as low as 18 mW/m-K at ambient pressure and those crosslinked with polyol had low flexural modulus at cryogenic temperatures. Applications of these aerogels in aerospace and diving are presented.

A 3D printed electromagnetic nonlinear vibration energy harvester

A 3D printed electromagnetic vibration energy harvester is presented. The motion of the device is in-plane with the excitation vibrations, and this is enabled through the exploitation of a leaf isosceles trapezoidal flexural pivot topology. This topology is ideally suited for systems requiring restricted out-of-plane motion and benefits from being fabricated monolithically. This is achieved by 3D printing the topology with materials having a low flexural modulus. The presented system has a nonlinear softening spring response, as a result of designed magnetic force interactions. A discussion of fatigue performance is presented and it is suggested that whilst fabricating, the raster of the suspension element is printed perpendicular to the flexural direction and that the experienced stress is as low as possible during operation, to ensure longevity. A demonstrated power of ∼25 μW at 0.1 g is achieved and 2.9 mW is demonstrated at 1 g. The corresponding bandwidths reach up-to 4.5 Hz. The system’s corresponding power density of ∼0.48 mW cm−3 and normalised power integral density of 11.9 kg m−3 (at 1 g) are comparable to other in-plane systems found in the literature.

Reduced shrinkage stress via photo-initiated copper(I)-catalyzed cycloaddition polymerizations of azide-alkyne resins

ObjectivesPolymerization shrinkage stress and factors involved in the stress development such as volumetric shrinkage and modulus were investigated in photo-CuAAC (photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition) polymerization and compared with conventional BisGMA-based methacrylate polymerization for their use as alternative dental resins. MethodsTri-functional alkyne and di-functional azide monomers were synthesized for photo-CuAAC polymerization. Conversion kinetics, stress development and polymerization shrinkage were determined with FTIR spectroscopy, tensometery, and with a linometer, respectively, for CuAAC and BisGMA-based monomer mixtures using a camphorquinone/amine visible light photoinitiator system. Thermo-mechanical properties for the cured polymer matrices were characterized by dynamic mechanical analysis and in three-point bending on a universal testing machine. Polymerization kinetics, polymerization shrinkage stress, dynamic volumetric shrinkage, glass transition temperature (Tg), flexural modulus, flexural strength, and flexural toughness were compared between the two different resin systems. ResultsA glassy CuAAC polymer (Tg=62°C) exhibited 15–25% lower flexural modulus of 2.5±0.2GPa and flexural strength of 117±8MPa compared to BisGMA-based polymer (Tg=160°C) but showed considerably higher energy absorption around 7.1MJ×m−3 without fracture when strained to 11% via three-point bend compared to the flexural toughness of 2.7MJ×m−3 obtained from BisGMA-based polymer. In contrast to BisGMA-based polymers at 75% functional group conversion, the CuAAC polymerization developed approximately three times lower shrinkage stress with the potential to achieve quantitative conversion under ambient temperature photocuring conditions. Moreover, relatively equivalent dynamic volumetric shrinkage of around 6–7% was observed via both CuAAC and dimethacrylate polymerization, suggesting that the low shrinkage stress of CuAAC polymerization was due to delayed gelation along with slower rate of polymerization and the formation of a more compliant network structure. SignificanceCuAAC crosslinked networks possessed high toughness and low polymerization shrinkage stress with quantitative conversion, which eliminated obstacles associated with BisGMA-based dental resins including limited conversion, unreacted extractable moieties, brittle failure, and high shrinkage stress.

A non-linear 3D printed electromagnetic vibration energy harvester

This paper describes a novel electromagnetic energy harvester that exploits the low flexural modulus of ABS and comprises of a nonlinear mechanism to enhance the generated power and bandwidth. The device is printed using desktop additive manufacturing techniques (3D printing) that use thermoplastics. It has a ‘V’ spring topology and exhibits a softening spring non-linearity introduced through the magnetic arrangement, which introduces a monostable potential well. A model is presented and measurements correspond favourably. The produced prototype generates a peak power of approximately 2.5mW at a frame acceleration of 1g and has a power bandwidth of approximately 1.2→1.5Hz and 3.5→3.9Hz during up and down sweeps respectively. The device has a power density of 0.4mW/cm3 at a frame acceleration of 1g and a density of 0.04mW/cm3 from a generated power of 25μW at 0.1g.

Mechanical properties of resin-ceramic CAD/CAM restorative materials

Statement of problemThe recent development of polymer-based computer-aided design and computer-aided manufactured (CAD/CAM) milling blocks and the limited availability of independent studies on these materials make it pertinent to evaluate their properties and identify potential strengths and limitations. PurposeThe purpose of this in vitro study was to determine and compare mechanical properties (flexural strength, flexural modulus, modulus of resilience) and compare the margin edge quality of recently introduced polymer-based CAD/CAM materials with some of their commercially available composite resin and ceramic counterparts. Material and methodsThe materials studied were Lava Ultimate Restorative (LVU; 3M ESPE), Enamic (ENA; Vita Zahnfabrik), Cerasmart (CES; GC Dental Products), IPS Empress CAD (EMP; Ivoclar Vivadent AG), Vitablocs Mark II (VM2; Vita Zahnfabrik), and Paradigm MZ100 Block (MZ1; 3M ESPE). Polished 4×1×13.5 mm bars (n=25) were prepared from standard-sized milling blocks of each tested material. The bars were subjected to a 3-point flexural test on a 10-mm span with a crosshead speed of 0.5 mm/min. In addition, 42 conventional monolithic crowns (7 per material) were milled. Margin edge quality was observed by means of macrophotography and optical microscopy, providing a qualitative visual assessment and a measurement of existing roughness. The results were analyzed by ANOVA followed by the Tukey HSD test (α=.05). ResultsThe mean flexural strength of the tested materials ranged from 105 ±9 MPa (VM2) to 219 ±20 MPa (CES). The mean flexural modulus ranged from 8 ±0.25 GPa (CES) to 32 ±1.9 GPa (EMP). The mean modulus of resilience ranged from 0.21 ±0.02 MPa (VM2) to 3.07 ±0.45 MPa (CES). The qualitative assessment of margin edge roughness revealed visible differences among the tested materials, with mean roughness measurements ranging from 60 ±16 μm (CES) to 190 ±15 μm (EMP). The material factor had a significant effect on the mean flexural strength (P<.001), flexural modulus (P<.001), modulus of resilience (P<.001), and margin edge roughness (P<.001) of the tested specimens. ConclusionsThe new-generation polymer-based materials tested in this study exhibited significantly higher flexural strength and modulus of resilience, along with lower flexural modulus values compared with the tested ceramic or hybrid materials. Crowns milled from the new resin-based blocks seemed to exhibit visibly smoother margins compared with the ceramic materials studied.

Effect of peroxide bleaching on the biaxial flexural strength and modulus of bovine dentin.

Objective:This study evaluated the effects of carbamide peroxide and hydrogen peroxide on the biaxial flexural strength and flexural modulus of bovine dentin.Materials and Methods:Thirty coronal dentin disks (0.5 mm thick × 6.0 mm diameter) were prepared from bovine teeth. The disks were randomly divided into three groups (n=10): A control group (unbleached), a group bleached with 10% carbamide peroxide (8 h at 37°C), and a group bleached with 38% hydrogen peroxide (three 10 min applications at 37°C). The specimens were tested in a biaxial flexural apparatus held in a universal testing machine at 1.27 mm/min until failure occurred, and the biaxial mechanical properties were calculated. For each test parameter, the data were statistically analyzed by Fisher's PLSD test (predetermined α = 0.05).Results:The group bleached with 38% hydrogen peroxide demonstrated significantly lower flexural strength than the unbleached control group. Hydrogen peroxide treatment resulted in a significantly lower flexural modulus compared with the control group and with carbamide peroxide bleaching.Conclusion:Exposure of dentin to hydrogen peroxide significantly reduced both the flexural strength and the flexural modulus compared with the no-treatment control, whereas exposure to carbamide peroxide did not significantly affect either parameter.

Fabrication and properties of PIP 3D Cf/ZrC–SiC composites

Three-dimensional (3D) Cf/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The Cf/ZrC–SiC composite with relatively more PIP cycles of PCS has a higher density and a lower porosity, which account for the improved mechanical property of the composite. The composite with 6 PIP cycles of PCS has a flexural strength of 136.0±13.1MPa, and a fracture toughness of 7.3±0.3MPam1/2, which is superior to the monolithic ultrahigh temperature ceramics. The relatively low flexural strength and elastic modulus of the Cf/ZrC–SiC composites are attributed to the small stiffness of the matrix because of the debonding feature of the ZrC matrix. The high temperature oxidation testing of the S6-Cf/ZrC-SiC composite reveals that the surface molten ZrO2 layer contributes mainly to the improved anti-ablation property.

Bacterial Viability and Physical Properties of Antibacterially Modified Experimental Dental Resin Composites

PurposeTo investigate the antibacterial effect and the effect on the material properties of a novel delivery system with Irgasan as active agent and methacrylated polymerizable Irgasan when added to experimental dental resin composites.Materials and MethodsA delivery system based on novel polymeric hollow beads, loaded with Irgasan and methacrylated polymerizable Irgasan as active agents were used to manufacture three commonly formulated experimental resin composites. The non-modified resin was used as standard (ST). Material A contained the delivery system providing 4 % (m/m) Irgasan, material B contained 4 % (m/m) methacrylated Irgasan and material C 8 % (m/m) methacrylated Irgasan. Flexural strength (FS), flexural modulus (FM), water sorption (WS), solubility (SL), surface roughness Ra, polymerization shrinkage, contact angle Θ, total surface free energy γS and its apolar γS LW, polar γS AB, Lewis acid γS +and base γS - term as well as bacterial viability were determined. Significance was p < 0.05.ResultsThe materials A to C were not unacceptably influenced by the modifications and achieved the minimum values for FS, WS and SL as requested by EN ISO 4049 and did not differ from ST what was also found for Ra. Only A had lower FM than ST. Θ of A and C was higher and γS AB of A and B was lower than of ST. Materials A to C had higher γS + than ST. The antibacterial effect of materials A to C was significantly increased when compared with ST meaning that significantly less vital cells were found.ConclusionDental resin composites with small quantities of a novel antibacterially doped delivery system or with an antibacterial monomer provided acceptable physical properties and good antibacterial effectiveness. The sorption material being part of the delivery system can be used as a vehicle for any other active agent.

Comparative evaluation of dental resin composites based on micron- and submicron-sized monomodal glass filler particles

ObjectivesA model resin composite containing a novel monomodal inorganic filler system based on submicron-sized Ba–Si–Al glass particles (NanoFine NF180; Schott) was formulated and compared with an experimental composite containing micron-sized particles (UltraFine UF1.0; Schott). MethodsThe filler particles were characterized using X-ray microanalysis and granulometry, while the composites were characterized in terms of filler–resin morphology, radiopacity, degree of CC conversion, hardness, flexural strength/modulus, work-of-fracture, surface roughness and gloss (before and after simulated toothbrushing abrasion), and bulk compressive creep. The composites were formulated from the same photoactivated dimethacrylate co-monomer, incorporating mass fractions of 75% micron- and 78% submicron-sized particles. Quantitative data were analyzed at a significance level of p<0.05. ResultsBoth filler systems exhibited a narrow grain size range (175±30 and 1000±200nm), with differences restricted to the size and specific area of the particles. The composites were similar in radiopacity, flexural strength, work-of-fracture, and creep. The submicron composite was harder but had lower flexural modulus and CC conversion. No significant differences in roughness were observed before brushing, although the submicron composite had higher gloss. Brushing increased roughness and decreased gloss on both materials, but the submicron composite retained higher gloss after brushing. SignificanceThe monomodal submicron glass filler system demonstrated potential for use in restorative dental composites, particularly due to improved esthetic properties.

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.

Enhancement of flexural properties and dimensional stability of rice husk particleboard using wood strands in face layers

Major drawbacks of rice husk particleboards are low flexural modulus and strength, and dimensional stability compared with strandboards made from wood strands. This study investigated the flexural properties and dimensional stability of the sandwich-structured composites comprising the rice husk particles in the core layer and randomly aligned the wood strands in the face layers. The design of three layer structure comprising a core layer of rice husk sandwiched between two ash wood strand layers were 5:90:5, 10:80:10, 15:70:15, 20:60:20 face:core:face ratios (by weight). The presence of the face strands significantly improved the flexural modulus and strength, and the dimensional stability. As compared with the rice husk particleboards, incorporation of 10–40% of the strands in the face layer of the specimens improved the flexural modulus and strength by 21–166% and 35–202%, respectively. The effect was most pronounced beginning with 30wt.% the wood strands. The sandwich-structured composites with the wood strands in the face layer (40wt.% of the panel weight) and the rice husk particles in the core layer (60wt.% of the panel weight) can be evaluated as a substitute for the strandboards in structural applications.