Significant Reinforcement Effect Research Articles

Comparative assessment of load-bearing capacities in bolted laminated bamboo lumber connections: A study on diverse reinforcement techniques

Laminated bamboo lumber (LBL), a renowned engineered bamboo composite known for its outstanding performance and sustainability, is extensively used in modern bamboo structured buildings. This study focuses on examining the effects of diverse reinforcement techniques, particularly self-tapping screws and tension control bolts, on the load-bearing capacity of bolted LBL connections with steel plates. In total, 24 specimens were categorized into 8 groups and subjected to monotonic loading tests. The test results demonstrate that the non-reinforced group clearly shows longitudinal splitting failure at the bolt position, followed by a decrease in load-bearing capacity after failure. In contrast, the group with self-tapping screws (ST) and tension control bolts (BT) exhibited fiber tearing at the lower part of the midspan, accompanied by section bending and damage. The final load-bearing capacity of the groups reinforced with single-row three-bolt self-tapping screws and tension control bolts showed an increase of 67.30 % and 52.95 %, respectively. Likewise, the groups with single-row four-bolt configurations also demonstrated significant reinforcement effects, with increases of 40.52 % and 29.66 %, respectively. Furthermore, DIC-3D analysis was employed to examine the displacement of the connection bolts, and the van der Put model was utilized to estimate the load-bearing capacity of bolted LBL connections under splitting conditions. Subsequently, finite element models were established and calibrated based on the experimental data. The results confirm that self-tapping screws and tension control bolts can serve as structural enhancements in the design of bolted LBL connections, providing effective reinforcement for existing engineering structures.

Can Social Learning Promote Farmers’ Green Breeding Behavior? Regulatory Effect Based on Environmental Regulation

Farmers’ green breeding behavior is significant to environmental protection and sustainable development. Based on the micro-survey data of 1248 beef cattle farmers in Inner Mongolia Autonomous Region and Jilin Province, the OLS model and regulatory effect tests are used to analyze the influence of social learning on farmers’ green breeding behavior and to verify the mechanism of environmental regulation. Key findings include the following: (1) Social learning has a significant positive impact on farmers’ green breeding behavior. (2) Social learning has a significant positive impact on farmers’ willingness to undertake green breeding, farmers’ specific behavior of green breeding, and farmers’ continuous green breeding, among which the effect on specific behavior of green breeding is the most positive. (3) Environmental regulation plays a moderating role in the relationship between social learning and farmers’ green breeding behavior, among which all sub-dimensions of environmental regulation (incentive-based environmental regulation, binding environmental regulation and guided environmental regulation) have positive reinforcing effects, especially the most significant reinforcement effect of binding environmental regulation. Based on the research conclusions, this study proposes policy suggestions such as strengthening the training of farmers, strengthening the learning and communication among farmers’ neighbors, increasing the frequency of farmers’ use of mass media, improving the environmental regulation policy system, and promoting the coordinated development of environmental, economic, and social benefits.

Numerical simulation of the deformation behavior of a composite foundation consisting of rubber particle loess-CFG under dynamic loading

The CFG pile technology is primarily employed for foundation reinforcement, offering cost-saving benefits and demonstrating significant reinforcement effects. Consequently, it has gained widespread utilization. However, due to its unique composition and exceptional strength characteristics, investigating the dynamic properties of rubber particle loess-CFG poses significant challenges. In this study, a numerical simulation approach is employed to investigate the dynamic characteristics of rubber particle loess-CFG and its deformation response under dynamic loading is analyzed. The results indicate that the deformation of rubber particle loess-CFG remains minimal under static loading, while it significantly increases under dynamic loading. However, the vertical and horizontal displacements at the top of the mattress layer are comparatively smaller than those observed in loess-CFG, highlighting their seismic stability. The mattress layer of the rubber particle loess-CFG undergoes vertical compression and deformation, while being horizontally squeezed towards the central region. The horizontal displacement and its variation range are significantly greater than that of the entire pile and the soil between piles. Therefore, it is crucial to analyze the material properties, thickness, and extent of the mattress layer during design in order to mitigate its influence. When subjected to dynamic loading at the base of the model, the rubber particle loess-CFG exhibits a strip distribution of vertical displacement which gradually decreases from bottom to top. Moreover, as focal depth increases, the impact of dynamic loading on foundation deformation diminishes. Consequently, rubber particle loess-CFG provides a dual functionality of enhancing foundation strength while effectively resisting dynamic deformations. These research findings provide a theoretical basis for designing reinforced foundations using rubber particle loess-CFG and offer an innovative approach for recycling waste tire rubber particles.

In-situ mullite whisker reinforced SiC porous ceramics with whiskers and bonding layers synchronously growing: Using CaF2 as a temperature-controlled whisker formation switch

Mullite-bonded SiC porous ceramics are of potential in hot gas infiltration while the insufficient mechanical performance limits its application. In-situ mullite whisker reinforcement is a potential solution but the formation temperature mismatch between mullite whisker and bonding layer is a challenge. In that case, mullite whiskers massively form ahead of the bonding layer excessively consuming alumina leading to poor bonding layers between SiC particles and thus, the mechanical performance. Herein, the mismatch was solved by using CaF2 as a temperature-controlled reaction switch. As a result, both the bonding layer and whisker synchronously formed. The material showed significant reinforcement effects, and exhibited a flexural strength of 124.8 MPa and a fracture toughness of 1.53 MPa·m1/2 with an open porosity of 36.6 vol%, realizing a breakthrough in the mechanical performance. Interestingly, an increase in oxygen vacancy concentration with the sintering temperature was first reported, which may benefit the whisker growth.

Experimental study on the mechanical behavior of EICP-casein-treated calcareous sand

In order to protect and develop marine resources, it is essential to reinforce the calcareous sand foundation on coral reefs during engineering construction. This study proposes a novel approach that combines enzyme-induced carbonate precipitation (EICP) with casein to solidify calcareous sand, which overcomes the issues of low calcium carbonate crystallization and insufficient cementation strength encountered in the pure EICP method. This study investigated the reinforcement effects and mechanisms of the combined method across various scales. Sonic time testing revealed an initial decline in sample density followed by a gradual increase, with the lowest density observed at 10% casein content. Sample strength depends on casein dosage and curing time. Overall, the trend in sample strength showed an initial decrease followed by a gradual increase, with 10% casein content again resulting in the lowest strength. The measured experimental groups achieved a minimum strength of approximately 1.17 MPa and a maximum strength of around 6.34 MPa. As casein concentration rises, the optimal curing time increases from 12–48 h. Microscopic experiments reveal casein expansion and dissolution in the EICP liquid, explaining UCS value changes with casein dosage and curing time. Combining scanning electron microscopy and microscopic experiments highlights the cementitious material’s vital role in strengthening samples. In conclusion, combining EICP and casein for solidifying calcareous sand is technically feasible and highly effective with significant reinforcement effects.

Tunicate cellulose nanocrystals reinforced modified calcium sulfate bone cement with enhanced mechanical properties for bone repair

Considering the poor mechanical properties of bone cement, its practical application has always been limited. In this study, we introduced tunicate cellulose nanocrystals (TCNCs) into calcium sulfate bone cement for the first time, and multiple enhanced composite bone cement was prepared by the condensation reflux method. Firstly, high-strength modified calcium sulfate hemihydrate (CSH) bone cement was successfully prepared by using tartaric acid, a crystal modifier with a chiral structure. Secondly, the inclusion of TCNCs not only exhibited significant reinforcement and toughening effects but also stimulated the adhesion, proliferation, and differentiation of related osteoblasts. Furthermore, TCNCs encapsulated the CSH particles, overcoming the limitations of excessive degradation rates in bone cement and enabling sustained release of Ca2+, promoting the healing of bone defects. Overall, this study presents novel ideas and methodologies for designing bone cement with exceptional performance. It also provides a new platform for the development of bone tissue engineering and is expected to become a new type of bone regeneration material. The utilization of oceanic resources in this context holds high-value potential, alleviating environmental burdens and providing clinically applicable bone tissue repair materials with broad application prospects.

Experimental Study and Bearing Capacity Analysis of Retrofitted Built-Up Steel Angle Members under Axial Compression

Against the update of load design standards and requirement of long-term service, many latticed towers using steel angles subjected to gradual performance degradation must be retrofitted for bearing further social functions, e.g., electric power transmission and fifth-generation mobile communication. Therefore, this paper proposed a non-destructive reinforcement method for steel angles by avoiding unnecessary new construction or complex reinforcement procedure. The non-destructive reinforcement of a steel angle is composed of a steel angle, reinforcement plate, and fixture. Standardized fixtures are used to connect the reinforcement plate and steel angle to achieve steel angle reinforcement. In retrofitting tests, built-up steel angle members were loaded under axial compression, in which the failure mode and reinforcement effect of key parameters (e.g., clamp type, slenderness ratio, and clamp distance) were analyzed and compared, where a significant reinforcement effect was obtained with the capacity increment within 39~174%; the clamp types and clamp distance had a slight effect on bearing capacity; and the proposed reinforcement method was more effective for slender members. Based on the mechanical mechanism analysis and failure mode, the accuracy of the design method for calculating the bearing capacity of those built-up steel angle members was suggested and verified, in which a simplified mechanical model for the flexural-buckling mode was developed. The design method based on AISC360-16 agreed well with the test result and could be effectively used for calculating the flexural–torsional bearing capacity of those built-up steel angles. This study can provide a valuable reference for the design and application of non-destructive reinforcement of angle steel towers.

Effect of Zr/Al binder ratio on properties of PCBN composites

Polycrystalline cubic boron nitride composites (PCBN) were synthesized by mixing cBN micro-powder, Zr powder and Al powder in different mass ratios under high temperature and ultra-high pressure conditions. The phase composition and microstructure of the composites were analyzed by X-ray diffraction and scanning electron microscopy. The effects of different Zr/Al mass ratios to the sintering behavior and related properties of PCBN composites were studied in order to obtain a binder ratio scheme with excellent performance. The research shows that when the Zr/Al ratio is 16 wt%:8 wt% (2:1), the hardness of the sample is the highest, which is 33.4 GPa, and the fracture toughness is the best 6.6 MPa·m1/2. Crack bifurcation, deflection and particle reinforcement have significant reinforcement and toughening effects on PCBN composites. When the Zr/Al ratio is 12 wt%:12 wt% (1:1), the PCBN composite with the best density is obtained, the porosity is as low as 0.7%, and the strength of the sample is the highest, which is 864.2 MPa.

Effect evaluation of grass roots on mechanical properties of unsaturated coarse-grained soil

The utilization of vegetation to prevent shallow slope failure and erosion has received significant attention in recent years, since it is recognized that vegetation has the mechanical and hydrological strengthening effect on soils. To accurately evaluate the mechanical properties of grassed soil and effect of grass age, grassed soils with grass ages of 2, 4, 6 and 8 months as well as bare soil are cultivated and prepared. Then, considering that grass layer in nature is usually situated above ground water table in the non-saturation state, a sequence of unsaturated triaxial tests are performed for soil specimens with different grass ages and matric suctions. Experimental results reveal that both grass root and matric suction enhance soil shear strength. The peak shear strength and cohesion of grassed soils tend to increase with increasing grass ages or matric suctions. Moreover, it is recognized that compared with grass root, the matric suction causes a more significant reinforcement effect for increasing total cohesion of soil sample. On the other hand, grassed soil has a higher water retention capacity, and under the same matric suction conditions, the soil specimen with older grass age have higher volumetric water content. Furthermore, the measured total cohesion for unsaturated soil is validated by the proposed calculation equation based on Vanapalli model, and the calculated results fit the measured results well. Calculated and experimental results have good agreement showing the proposed equation can properly reflect the increase in the unsaturated mechanical properties of grassed soil.

Impact of Dicranopteris linearis roots on the shear strength of different soil layers in collapsing wall of Benggang

Abstract‘Benggang’ is a local term for a widespread type of severgully erosion with steep collapsing walls in granitic, low, hilly areas of southern China, and its development and expansion are closely related to the shear strength of the collapsing wall. Plant roots play an important role in improving soil shear strength. However, the shear strength of root‐soil complexes in different layers of collapsing walls remains obscure. We selected Dicranopteris linearis fern roots and adopted the direct shear method to evaluate the effect of root weight density (RWD) (0–1.25 g 100 cm−3) on the shear properties of the lateritic, sandy and detritus layers. The results showed that roots could enhance soil shear strength, and the maximum increase in the lateritic layer was 11.53%, higher than that in the sandy (5.84%) and detritus layers (3.17%). As the root content increased, the cohesion of the sandy and detritus layers increased and then decreased, and their maximum increase in cohesion and the fitting optimal RWD were lower than those of the lateritic layer. The internal friction angle was not affected by roots. When the root content was constant, the shear strength and cohesion of the lateritic layer were significantly higher than those of the sandy and detritus layers, while their internal friction angle was significantly lower than that of the latter two layers. The average increment of soil cohesion calculated by the Wu‐Waldron model (WWM) was 10.52 kPa, which was 0.30, 3.75 and 19.38 times the measured average values of the lateritic, sandy and detritus layers, respectively. The correction coefficient k′ was 0.02–1.18, and the in the lateritic layer was the highest (0.82), followed by that in the sandy and detritus layers. By combining the modified WWM with Coulomb's formula, new shear strength equations for root‐soil complexes of D. linearis were established. The predicted shear strength compared well with the measured shear strength (R2 > 0.90, NSE >0.90). Overall, the roots only had a significant reinforcement effect on the lateritic layer, and they could still not change the mechanical properties of the collapsing wall, which were more stable in the upper layers and weaker in the bottom. Therefore, other measures should be taken in the bottom layers to improve the stability of Benggangs.Highlights Effect of D. linearis roots on the shear strength of collapsing walls in Benggang was studied. Roots could improve collapsing‐wall soil shear strength, mainly reflected in the cohesion. The roots enhancement effect in lateritic layer was better than that of sandy and detritus layers. New shear strength equations of root‐soil complexes were established based on the Wu‐Waldron model.

The role of market competition for knowledge competencies, R&D and innovation: an empirical analysis for German firms

PurposeKnowledge competencies and (R&D) activities are one of the most important sources of innovation and have been widely discussed in the literature. In comparison, the role of the competitive environment for the innovation activities of firms is still open to debate and has not been fully understood yet. Therefore, this paper intends to provide new evidence on the interaction between knowledge competencies and R&D activities of firms on the one side and their competitiveness in the market environment on the other. In particular, the moderating function of market competition is explored. In this respect, the analysis covers the main innovation types as well as both sectors, manufacturing and services.Design/methodology/approachThe empirical analysis is based on a three years panel dataset of German manufacturing and service firms obtained from Mannheim Innovation Panel (MIP) and Community Innovation Surveys (CISs: 2011, 2013 and 2015). For the estimation, a binary instrumental variable treatment model with Heckman selection method is used. Also, it provides a suitable approach to estimating the binary variables in order to cope with endogeneity concerns.FindingsThe estimation results show that R&D activities and knowledge competencies are positively related to innovation activities of different types conditioned on firms' specific perception of their competitive environment, in terms of outdated products/services as well as strong competition from abroad. Most importantly, the results from the moderation estimation reveal that there is a significant difference between the manufacturing and service sector. Service firms engage more in internal R&D activities on generating product innovations while the manufacturing firms conduct more external R&D on specific types of innovation. Further, the authors find that strong competition from abroad positively and significantly reinforces the effect of knowledge competencies on innovation activities for more types in services than in manufacturing. In contrast, outdated products and services tend to decline the effect of knowledge competencies for some innovation types in both sectors. The authors also observe a positive and significant reinforcement effect on knowledge competencies. However, it is found more beneficial for service firms since they can employ more innovation strategies.Originality/valueThe focus of the study is mainly on the impact of firms' competitive environment on innovation activities in various types through its interaction with knowledge competencies and R&D activities, across manufacturing and service firms.

Extrusion Printed Silk Fibroin Scaffolds with Post-mineralized Calcium Phosphate as a Bone Structural Material.

Artificial bone materials are of high demand due to the frequent occurrence of bone damage from trauma, disease, and ageing. Three-dimensional (3D) printing can tailor-make structures and implants based on biomaterial inks, rendering personalized bone medicine possible. Herein, we extrusion-printed 3D silk fibroin (SF) scaffolds using mixed inks from SF and sodium alginate (SA), and post-mineralized various calcium phosphates to make hybrid SF scaffolds. The effects of printing conditions and mineralization conditions on the mechanical properties of SF scaffolds were investigated. The SF scaffolds from ~10 wt% SF ink exhibited a compressive modulus of 240 kPa, which was elevated to ~1600 kPa after mineralization, showing a significant reinforcement effect. Importantly, the mineralized SF 3D scaffolds exhibited excellent MC3T3-E1 cell viability and promoted osteogenesis. The work demonstrates a convenient strategy to fabricate SF-based hybrid 3D scaffolds with bone-mimetic components and desirable mechanical properties for bone tissue engineering.

Mechanical, flowing and microstructural properties of cemented sulfur tailings backfill: Effects of fiber lengths and dosage

In this paper, the mechanics, flowing and microstructural properties of the cemented sulfur tailings backfill (CSTB) have been studied by means of flow performance test, uniaxial compression test, scanning electron microscope test and X-ray energy spectrum test. On the basis of previous results, a new way was proposed to improve the mechanical performance of CSTB. The research results show that the fluidity of sulfur tailings slurry increases exponentially with the increase of sulfur content, because the density of sulfide concentrate is greater than that of tailings. The adding of polypropylene fiber will reduce the fluidity of sulfur tailings slurry and the fluidity of the slurry decreases exponentially with the increase of fiber content. The compressive strength and 28d splitting tensile strength of the CSTB both increased first and then decreased with the increase of the sulfur content, and reached the maximum when the sulfur content was 12%. However, the CSTB exhibits obvious strength deterioration characteristics when the curing age exceeds 28 days. The compressive strength and 28d tensile strength of the CSTB both increased first and then decreased with the increase of fiber content, and then, reached the maximum when the fiber content is 0.6%. In addition, the effect of adding polypropylene fiber on improving the tensile strength is better than that of compressive strength. SEM and X-ray energy spectrum analysis results show that a certain amount of secondary gypsum and ettringite crystals can effectively fill the pores in the CSTB, which contributes to the development of strength. However, when the sulfur content exceeds the critical content, there are obvious pore structures and a large number of expansive minerals such as gypsum and ettringite in the CSTB, which leads to the strength deterioration of the CSTB. The special spatial skeleton structure formed by polypropylene fibers in the CSTB matrix can play a significant physical reinforcement effect and the reinforcement effect is mainly controlled by the bonding effect between the fiber and the CSTB matrix interface. In addition, the compressive strength, tensile strength and fluidity prediction models of the fiber reinforced CTSB constructed based on the fiber modification coefficient can accurately predict the compressive strength, tensile strength and fluidity parameters, which can provide certain guidance for engineering applications.

Study On the Influence of Micro-Steel Pipe Pile Reinforcement and Soil Structure on Landslide Stability in Geological Engineering

Micropile is a new type of supporting structure, which is characterized by rapid and convenient construction, flexible pile layout and significant reinforcement effect. In this paper, combined with a landslide case, the influence of micro steel pipe pile reinforcement on the displacement, stress, strain and stability of the landslide is preliminarily studied by using finite element analysis simulation software. The results show that the reinforcement of micro-steel pipe piles improves the slope stability, but it is still in an unstable state. In the later stage, the landslide can be effectively controlled by adjusting the reinforcement scheme and the parameters of piles, such as material grade and pile density.

Reinforcing effects in elastomeric composites, filled with particles of mineral fillers, based on silicon dioxide and carbon

When creating elastomeric composites, structures and products made from such materials, considerable attention is paid to environmental issues, as well as to improving economic efficiency and energy efficiency in its production. In this regard, the development of new types of strengthening highly dispersed fillers for elastomeric and polymer composite materials, including those of natural origin, providing an optimal balance of mechanical properties of composites and having advantages over existing solutions, is an actual task. In the course of the work, a technology was developed for producing highly dispersed fillers by ultrafine grinding of raw materials. The obtained experimental data shows a significant reinforcement effect (up to five times) with a decrease in the average particle size of the filler. It is established, that he most effective filler, in terms of reinforcement, are particles based on amorphous silicon dioxide, obtained from rice husk processing products and shungite rock. The significant influence of the surface functionality and the carbon/silicon dioxide ratio of submicron filler particles on the mechanical properties of elastomeric composites is shown. It is established that new classes of reinforcing fillers can be recommended for practical use in the future.

Super-flexible polyimide nanofiber cross-linked polyimide aerogel membranes for high efficient flexible thermal protection

• Novel super-flexible PI nanofiber crosslinked PI aerogel membrane was prepared. • The crosslinked structure realized the transition from brittleness to flexibility. • The lightweight membranes exhibited ultra-low thermal conductivity of 0.0279 W/mK. • The membranes showed high-temperature resistance and ultrahigh tensile modulus. Experimental preparation of lightweight and highly flexible aerogels has been a longstanding challenge, which limits their practical application in flexible thermal protection. Here, polyimide (PI) nanofiber cross-linked polyimide aerogel membranes were designed to achieve high flexibility, strong mechanical properties, and highly efficient heat-insulated performance. By taking full advantage of the perfect chemical compatibility and robust interfacial bonding strength between PI nanofibers and PI aerogel molecular chains, the PI aerogel membranes achieved the significant transformation from brittleness to high flexibility. The results demonstrate the addition of PI nanofibers exhibits significant reinforcement and toughening effect. PI nanofiber cross-linked PI aerogel membranes possess low density of 0.168 g/cm 3 and low thermal conductivity of 0.0279 W/mK. Moreover, 20 wt% PI nanofiber cross-linked PI aerogel membranes exhibit high tensile strength of 2.95 MPa, while the tensile strength of pure PI aerogel is 0.27 MPa. The as-prepared PI aerogel membrane exhibited high-temperature flexible thermal protection performance, which made it a candidate for the application in modern technology, military, and aerospace.

Investor attention shocks and stock co-movement: Substitution or reinforcement?

The impact of investor attention allocation shocks on firm-level stock return co-movements with the market remains of great interest. Recent papers study this issue while showing that large national lottery jackpots act as shocks to investor attention. This paper contributes substantially to this stream of investigation. Motivated by studies in behavioral finance, we frame the role of shocks to investor attention as either substituting for investor attention or reinforcing it, with co-movements between the stock-level and the market level either increasing or decreasing respectively. We identify, in contrast to other studies, an economically significant reinforcement effect for the Chinese market. We find generally that large lottery jackpots increase, rather than decrease, allocation of investor attention to individual stocks, and, consequently, stock return co-movements with the market decrease rather than increase. An exception is the bear market of 1st January 2011–21st May 2014, where we find, as in earlier studies, jackpots associated with decreased attention. Compared to recent work on national lotteries and investor-attention allocation, our findings suggest far more contextual nuance to this topic than previously acknowledged. Our results should be of great interest to scholars interested in the impact of investor-attention allocation on financial markets, as well as to investment professionals.

Development and assessment offluorinated grapheme nanoparticles modified dental adhesives

Background: The success of adhesion to the tooth structure plays an important role in the dental restoration,which can effectively avoid the terrible clinical problems during the bonding process, including the secondarycaries and the loading of adhesive compositions with fillers and nanoparticles with antibacterial propertieshas led to a significant reinforcement effect of the adhesive.Objective: The current study is designed to investigate the effects of addition of 2% of fluorinated grapheneon the adhesive-dentin hybrid layer for two types of commercially available universal adhesive, guidedusing the etch and rinse technique as a bonding procedure.Method: Forty extracted premolar teeth will be divided into four groups of ten teeth. Group I: the nonincorporated (Prime & Bond Universal) bonding agent (Control group). Group II:using the 2% FGnanoparticles incorporated (Prime & Bond Universal) bonding agent. Group III: non-incorporated (AllBond Universal) bonding agent (Control group). Group IV: using the incorporated (All Bond Universal)bonding agent. The degree of conversion was also measured using Fourier transform infrared spectroscopy(FTIR). The antibacterial activity of the adhesives was evaluated using agar diffusion test against thefollowing bacteria: Streptococcus mutans and Lactobacillus salivarius obtained from saliva.Results: A significantly greater antibacterial activity was obtained with adhesives containing a 2% fluorinatedgrap hene nanoparticles than other groups (P<.01). Degree of conversion of tested adhesives was not changesignificantly after addition of 2% of fluorinated grap hene nanoparticles.Conclusion: The antibacterial effect of adhesives that incorporated with 2% of fluorinated graphenenanoparticles was higher than the non-incorporated etch- and rinse adhesive systems. The degree ofconversion of adhesives was not significantly different.

Copernicia Prunifera Leaf Fiber: A Promising New Reinforcement for Epoxy Composites.

A basic characterization of novel epoxy matrix composites incorporated with up to 40 vol% of processed leaf fibers from the Copernicia prunifera palm tree, known as carnauba fibers, was performed. The tensile properties for the composite reinforced with 40 vol% of carnauba fibers showed an increase (40%) in the tensile strength and (69%) for the elastic modulus. All composites presented superior elongation values in comparison to neat epoxy. Izod impact tests complemented by fibers/matrix interfacial strength evaluation by pullout test and Fourier transformed infrared (FTIR) analysis revealed for the first time a significant reinforcement effect (> 9 times) caused by the carnauba fiber to polymer matrix. Additional thermogravimetric analysis (TG/DTG) showed the onset of thermal degradation for the composites (326 ~ 306 °C), which represents a better thermal stability than the plain carnauba fiber (267 °C) but slightly lower than that of the neat epoxy (342 °C). Differential scanning calorimetry (DSC) disclosed an endothermic peak at 63 °C for the neat epoxy associated with the glass transition temperature (Tg). DSC endothermic peaks for the composites, between 73 to 103 °C, and for the plain carnauba fibers, 107 °C, are attributed to moisture release. Dynamic mechanical analysis confirms Tg of 64 °C for the neat epoxy and slightly higher composite values (82–84 °C) due to the carnauba fiber interference with the epoxy macromolecular chain mobility. Both by its higher impact resistance and thermal behavior, the novel carnauba fibers epoxy composites might be considered a viable substitute for commonly used glass fiber composites.

Reinforcement of Waterborne Polyurethane Films with Poly(acrylic acid)-Modified Palygorskite Fibers

Palygorskite (PAL) is a natural fibrous clay mineral which attracted tremendous attention as reinforcing agent to polymers. In this paper, a facile and environmental friendly modification process of PAL by poly acrylic acid (PAA) via in-situ polymerization in PAL/water gel has been reported. The effects of PAA modified PAL (PAA-PAL) on the mechanical and thermal properties of waterborne polyurethane (WPU) nanocomposites have been investigated. Scanning electron microscopy (SEM) demonstrated that the dispersion of PAL has improved dramatically after PAA modification. Tensile tests showed that PAA-PAL has a significant reinforcement effect on WPU matrix. Addition of 10 wt% PAA-PAL, the tensile strength and the Young’s modulus of WPU composites increased 235 % and 388 %, respectively. Furthermore, the thermal stability of WPU also has been distinctly improved via addition of PAA-PAL.