Improved mechanical and thermal properties of bamboo–epoxy nanocomposites

Natural fiber‐reinforced hybrid composites based on bamboo/epoxy/nanoclay were prepared. Ultrasound sonication was used for the dispersion of nanoclay in the bamboo–epoxy composites. The morphology of bamboo–epoxy nanocomposites was investigated by using scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The results show that there exists an optimum limit in which the mechanical properties of composites improved by continuously increasing the nanoclay content. The tensile and flexural strength of bamboo–epoxy nanocomposites with 3 wt% nanoclay increased by 40% and 27%, respectively, as compared to pure composites. The highest value of impact strength was obtained for 1 wt% nanoclay content bamboo–epoxy nanocomposites. The enhanced impact strength of bamboo–epoxy nanocomposites was one of the key advantages brought by nanofiller. The results show that incorporation of nanoclay substantially increases the water resistance capability and thermal stability of bamboo–epoxy nanocomposites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Characterization of nanocomposite laminates fabricated from aqueous dispersion of nanoclay

Preparation of E‐glass/waterborne epoxy prepregs containing natural nanoclay and properties of their composites are presented. Prepregs were prepared by wetting randomly oriented, chopped glass fiber preforms with aqueous dispersion of EpiRez 3522‐W‐60 resin, dicyandiamide, 2‐methylimidazole and natural nanoclay (Cloisite® Na⁺). The nanoclay content of the aqueous dispersion was adjusted to yield final nanoclay contents of 0, 1, 2, and 4 wt%, whereas the glass fiber content is kept constant at 47 wt%. These prepregs were then used to fabricate disk‐shaped composite samples by APA2000 rheometer. Composite samples were tested for interlaminar shear strength, flexural stiffness, and glass transition temperature. The flexural stiffness was observed to increase by more than 26% over the range of nanoclay loading, despite a 13% decrease in interlaminar shear strength. Similarly, glass transition temperature increased from 89°C to above 94°C for the samples comprising 4 wt% nanoclay. X‐ray diffraction analyses indicated 48% increase in the gallery spacing suggesting strong intercalation of the nanoclay platelets by the epoxy matrix. Microstructural observations of the fracture surfaces and polished surfaces show significant differences in the matrix topology and fiber to matrix adhesion. The composites with higher nanoclay content depict uniform and submicron surface features implying homogenous dispersion of nanoclay. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effects of nanoclay on the properties of cardanol‐modified‐resol‐epoxy‐novolac composite material

A nanocomposite based on nanoclay and resol that was modified with cardanol, a natural alkyl phenol, shows improvement for the glass‐fiber‐reinforced epoxy‐composite system. Dispersion of the nanocomposite was investigated by X‐ray, showing good results obtained by the in situ polymerization method. The mechanical properties of the final composites were improved by doping a 6 wt% of nanoclay in cardanol‐modified‐resol (CMR) into the epoxy matrix. The results show that a 15 wt% of CMR in epoxy is a most suitable ratio. Using polyamide as a curing agent instead of other traditional systems, such as anhydrides or amines for epoxy resin, overcame important limitations, further allowing for improved processability. The overall composite performance was enhanced. Additionally, the thermal stability of the system was investigated by thermal gravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3238–3242, 2007     

Fabrication and characterization of functionally graded nanoclay/glass fiber/epoxy hybrid nanocomposite laminates

In this work, hardness, tensile, impact, bearing strength and water absorption tests were performed to study the mechanical properties of stepwise graded and non-graded hybrid nanocomposites. Three different stepwise graded nanocomposites and one non-graded (homogeneous) nanocomposite with the same geometry and total nanoclay content of 10 wt% were designed and prepared. Moreover, one neat glass fiber laminate was manufactured. The results of the tests indicated that addition of the graded and non-graded nanoclay improves hardness over neat glass fiber reinforcement. The maximum increase in hardness of about 53% over neat specimen is obtained for specimens that have the highest weight percentage (2 wt%) of the clay nanoparticles on its surface (S-specimen and the side of F-specimen that reinforced with 2 wt% nanoclay). The gradation process results in an increase in hardness of about 11% compared with non-graded (homogeneous) specimen. In addition, an improvement of 11.9% in strain-to-failure is achieved with specimen having greatest amount of nanoclay in the middle over neat glass fiber/epoxy composite. The other nanoclay-filled glass fiber composites have strain-to-failure close to neat glass fiber/epoxy. The addition of nanoclay reinforcement has insignificant effect on ultimate tensile strength, tensile modulus, water absorption, bearing strength and impact strength compared with neat glass fiber/epoxy.     

Effect of Nanoclay on the Impact Properties of Glass Fiber-Reinforced Polymer Composites

This paper presents the influence of nanoclay and E-glass fibre reinforcement on impact response in polymer composite laminates under low velocity impact loading conditions. Glass fibre reinforced epoxy/nanoclay composites were prepared by hand lay-up techniques. Morphological studies using SEM and XRD revealed that fully intercalation of nanoclay in epoxy system. The result showed that the energy absorption became more efficient and also increased by 21% for CSM fibre composites at the velocity of 4.42 m/s, when 3% nanoclay was added. The fracture surface of the nanocomposites was analyzed using the Scanning electron microscopy (SEM) to characterize the damage progression.     

Effect of nanoclay particles on mold‐filling performance in composites made via resin infusion process

This study investigates the effect of 3 and 5 wt% nanoclay (Cloisite 30B) addition on mold filling time and performance of continuous glass filament mat reinforced unsaturated polyester (UP) resin composites made by vacuum infusion process. X‐ray diffraction and transmission electron microscopy analysis as well as viscosity change in liquid state resin confirmed intercalation and exfoliation of the nanoclay in the resin system. The result shows mold filling time increase of 3 and 2.4 times for the samples containing 3 and 5 wt% nanoclay, respectively, compared with nanoclay‐free sample. This increase in mold filling time is directly attributed to the increase in resin viscosity. Filtration of nanoclay particles were observed in the resin flow direction. Result showed 8 and 14% filtration of nanoclay in flow direction for the samples with 3 and 5 wt% nanoclay content, respectively. Nanoclay containing specimens prepared from near resin entry port area showed relatively higher flexural and tensile modulus and as well as strength compared to specimens prepared from area close to vacuum port area. The result showed best performance for 3 wt% nanoclay containing specimen. However, impact strength decreased about 6.1 and 10.8% for 3 and 5% nanoclay, respectively. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Studies on the mechanical properties of composites reinforced with nanoparticles

In this article, the influence of nanoclay Closite 30B on the tensile, the flexural and the punch properties of 2D woven Glass/Epoxy laminate composite have been investigated experimentally. The glass/epoxy/nanoclay laminate have 12 layers and 50% fiber volume fraction is manufactured by VRTM method. Fibers have a plain‐weave configuration with density of 200 g/m², while the nano‐epoxy resin system is made of diglycidyl ether of bisphenol A (Epon828) resin with jeffamine D400 as the curing agent and an organically modified modified montmorillonite in a platelet form, namely Closite 30B. The nanoclay is dispersed into the epoxy system in a 0, 1, 2, 3, 5, and 7% ratio in weight with respect to the nano‐matrix. The results have shown that the maximum improvement in the tensile strength, the failure strain, and toughness are 13, 7, and 27%, respectively, by 7% nanoclay and in the modulus is 9% by 3% nanoclay. The results of three bending flexural test indicate that the maximum improvement in the flexural strength and flexural modulus are 11 by 3% nanoclay and 48 by 5% nanoclay, respectively. Moreover, the result of punch tests have shown that the maximum improvement in energy absorbed is close to 46 by 5% nanoclay for crosshead speed of 1mm/min and close to 23 by 3% nanoclay for crosshead speed of 100 mm/min. POLYM. COMPOS., 38:205–212, 2017. © 2015 Society of Plastics Engineers     

Liquid crystalline matrix polymers for aramid ballistic composites

Five semi‐flexible thermotropic liquid crystalline (LC) polyesters and poly(ester‐amide)s were synthesized and used as matrix resins for Twaron™ aramid‐based ballistic fabrics. The ballistic performance was investigated as a function of the neat resin content. For the most successful liquid crystalline polyester system, the effect of blending with styrene‐ethylene‐butylene‐styrene (SEBS) and polyvinyl butyrate (PVB) rubber was also explored. The best neat resin V50 values were obtained for 20 wt% LC polyester (LCPE)‐Twaron™ composites, that is, 418 m.s⁻¹, whereas SEBS/LCPE and PVB/LCPE modifications resulted in maximum V50 values of 460 and 466 m.s⁻¹, respectively. It was found that the ballistic impact resistance is strongly influenced by the elastic modulus of the resin component and to a lesser extent to the level of adhesion between the resin and fabric. The effect of resin content, resin strength, elongation‐at‐break, and resin toughness on the ballistic impact resistance was found to be small. The best ballistic protection could be obtained when the Young's modulus of the LC resin was in the range of 0.01–1 GPa. This result seems to be in agreement with existing inter‐yarn friction models. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Crashworthiness of automotive composite material systems

The energy absorption capability of a composite material is important in developing improved human safety in an automotive crash. In passenger vehicles, the ability to absorb impact energy and be survivable for the occupant is called the crashworthiness of the structure. The crashworthiness in terms of the specific energy absorption (SEA) of a chopped carbon fiber (CCF) composite material system was compared with that of other fiber resin systems such as graphite/epoxy cross‐ply laminates (CP#1 and CP#2), a graphite/epoxy‐braided material system (O), and a glass‐reinforced continuous‐strand mat (CSM). The quantity of these material systems needed to ensure passenger safety in a midsize car traveling at various velocities was calculated and compared. The SEA of the chopped carbon fiber composite material was the highest compared to that of all the other composites investigated. It was calculated that only 4.27 kg of it would need to be placed at specific places in the car to ensure passenger safety in the event of a crash at 15.5 m/s (35 mph). This clearly led to an important practical conclusion that only a reasonable amount of this composite material is required to meet the necessary impact performance standard. The CCF composite tested at 5 mm/min crushing speed met both the criteria that need to be satisfied before a material is deemed highly crashworthy: A high magnitude of energy absorption and a safe allowable rate of this energy absorption. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3218–3225, 2004     

High velocity impact behavior of GRP panels containing coarse‐sized sand filler

Ballistic performance of glass reinforced plastic (GRP) composite plates containing coarse sized sand filler was investigated as an attempt towards developing a low cost armored system. In all, 10 different types of plates from 4 to 12 layers of E‐glass chopped strand mat reinforced polyester resin containing 0, 10, and 20% of 600‐ to 700‐μm sized sand filler were tested. A smooth barrel gas gun was used to conduct high velocity tests in the range of 70–185 m/s. Results indicated higher ballistic performance for GRP plates with sand filler in terms of higher ballistic limits (velocity at which at least 50% of samples were partially or fully penetrated the target plates with zero residual velocity), particularly for plates with highest sand filler loadings. Energy absorption associated with these specimens also showed higher performance. Delamination was identified as dominant failure mode, in particular for thicker specimens with highest sand filler loading. Specific energy absorption per weight per unit area for the composite plates indicated diminishing effectiveness with increase in sand filler loading, thereby limiting its possible application to armored system for stationary objects only. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Comparison of mechanical and ballistic performance of composite laminates produced from single‐layer and double‐layer interlocked woven structures

Textile structures have become quite popular as reinforcement materials in composite laminates due to their high impact‐damage tolerance and energy absorption ability. The impact performance of textile composites is not only affected by the type of fiber/matrix but also by the fabric structure used as reinforcement. The aim of this study was to compare the mechanical and ballistic performance of composite laminates reinforced with single‐layer and double‐layer interlocked woven fabrics. Kevlar^®−29 multifilament yarn was used for preparation of all the fabric structures and epoxy resin was used as the matrix system. The composites were produced using a hand lay‐up method, followed by compression molding. The mechanical and ballistic performance of composites reinforced with single‐layer and double‐layer interlocked woven fabrics was investigated in this study. The energy absorption and mechanical failure behavior of composites during the impact event were found to be strongly affected by the weave design of the reinforcement. The composites reinforced with double‐layer interlocked woven fabrics were found to perform better than those comprising single‐layer fabrics in terms of impact energy absorption and mechanical failure. POLYM. COMPOS., 35:1583–1591, 2014. © 2013 Society of Plastics Engineers     

Novel polymer‐ceramic composites for protection against ballistic fragments

For the first time, internally reinforced aggregate polymer ceramic composites were evaluated against fragment simulating projectiles (FSPs) of various calibers to investigate their ballistic impact response. Samples were prepared by mechanically mixing B₄C and cBN over a range of ratios and combinations with either thermosetting phenolic or epoxy resin and aramid pulp. Dry mixtures were then molded in a closed die using a heated platen press. The resulting tiles were then mounted as “strike faces” to an aramid backing material using an epoxy resin. Backed targets were tested in a fully instrumented firing range against 5.56 mm FSPs to test ballistic limit. A further series of tests using 7.62, 12.5, and 20 mm FSPs was conducted to examine round deformation across a range of fragments calibers. Round deformations were measured after impact and plotted against shot velocity. It was found that the polymer ceramic composite materials were effective round deformers and, like sintered ceramic strike faces, demonstrated improved ballistic performance at an equivalent areal density and impressive multihit capability. POLYM. COMPOS., 2012. © 2013 Society of Plastics Engineers     

Experimental study of sharp‐tipped projectile perforation of GFRP plates containing sand filler under high velocity impact and quasi‐static loadings

Penetration and perforation behavior of glass fiber reinforced plastic (GFRP) plates containing 20% sand filler have been investigated via high velocity impact tests using sharp tipped (30°) projectile and quasi‐static perforation tests. Two size sand filler (75 and 600 μm) were used in 4‐, 8‐, and 14‐layered laminated composite plates to study sensitivity of filler size toward loading system. Composite plates were examined for perforation load rate at 5 mm/min and high‐velocity impact loading up to 220 m/s. Results indicated higher energy absorption for GFRP plates containing sand filler for both high‐velocity impact and quasi‐static perforation tests. Higher ballistic limits were recorded for specimens containing sand filler. The study showed clear role played by coarse‐sized sand filler as a secondary reinforcement in terms of higher energy absorption as compared with nonfilled and specimens containing fine‐sized fillers. The investigation successfully characterized behavior of quasi‐static test during penetration and perforation of the sharp‐tipped indenter as an aid for impact application studies. Residual frictional load in the specimens containing sand filler constituted considerable portion of load bearing during perforation in quasi‐static tests. Delaminations followed by fiber and matrix fracture were major failure mode in high‐velocity tests and the main energy absorbing mechanism in thick‐walled plates, whereas in quasi‐static tests the failures were more of matrix fracture and fiber sliding. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Development of Anti-Ballistic Board from Ramie Fiber

A laminate of a composite was developed from Kevlar 29-ramie fiber reinforced by polyester resin for hard body armor. The focused given to the ballistic limit, maximum energy absorption, composite failure mode, lifetime rupture, target geometry and environmental effects. The results indicated that the maximum ballistic limit at impact speed is 623.97 m/s for a 15-mm target thickness and 837 m/s for a target thickness of 25 mm. The targets were improved in terms of the impact response with increasing relative humidity in the range of 50% ± 20% but were relatively decreased in terms of resistance with increasing temperature.     

Nanoclay Addition and Core Materials Effect on Impact and Damage Tolerance Capability of Glass Fiber Skin Sandwich Laminates

This study explores the effects of modified (OMMT) nanoclay and core material on low velocity impact behavior and damage tolerance capability of glass fiber reinforced (FRP) polyester resin – polystyrene foam (PS) sandwich laminates. The FRP and sandwich laminates are prepared by a compression molding technique for investigation. Low velocity impacts are carried out on all the fabricated laminates by using a instrumented drop weight impact tower with the energy level of 30 J and load–energy–time plots were recorded using data acquisition software. Post impact flexural tests have been conducted to evaluate the damage tolerance capability of the fabricated composite laminates. X-ray Diffraction (XRD) results have been obtained for the samples, where the nanoclay has indicated that intergallery spacing of the layered clay increases with the matrix. Scanning Electron Microscopy (SEM) has given the morphological picture of the nanoclay dispersion in the polymer fracture samples. The results of the study show that the impact properties and damage tolerance capability of the 4% nanoclay polyester sandwich have been greatly increased.     

Hybrid multi‐scale epoxy composites containing conventional glass microfibers and electrospun glass nanofibers with improved mechanical properties

A mechanically flexible mat consisting of structurally amorphous SiO₂ (glass) nanofibers was first prepared by electrospinning followed by pyrolysis under optimized conditions and procedures. Thereafter, two types of hybrid multi‐scale epoxy composites were fabricated via the technique of vacuum assisted resin transfer molding. For the first type of composites, six layers of conventional glass microfiber (GF) fabrics were infused with the epoxy resin containing shortened electrospun glass nanofibers (S‐EGNFs). For the second type of composites, five layers of electrospun glass nanofiber mats (EGNF‐mats) were sandwiched between six layers of conventional GF fabrics followed by the infusion of neat epoxy resin. For comparison, the (conventional) epoxy composites with six layers of GF fabrics alone were also fabricated as the control sample. Incorporation of EGNFs (i.e., S‐EGNFs and EGNF‐mats) into GF/epoxy composites led to significant improvements in mechanical properties, while the EGNF‐mats outperformed S‐EGNFs in the reinforcement of resin‐rich interlaminar regions. The composites reinforced with EGNF‐mats exhibited the highest mechanical properties overall; specifically, the impact absorption energy, interlaminar shear strength, flexural strength, flexural modulus, and work of fracture were (1097.3 ± 48.5) J/m, (42.2 ± 1.4) MPa, (387.1 ± 9.9) MPa, (12.9 ± 1.3) GPa, and (30.6 ± 1.8) kJ/m², corresponding to increases of 34.6%, 104.8%, 65.4%, 33.0%, and 56.1% compared to the control sample. This study suggests that EGNFs (particularly flexible EGNF‐mats) would be an innovative type of nanoscale reinforcement for the development of high‐performance structural composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42731.     

Epoxy/POSS organic–inorganic hybrids: Viscoelastic,mechanical properties and micromorphologies

A series of epoxy resin (EP)/octa(aminpropyl)silsesquioxane (POSS‐NH₂) organic–inorganic hybrid composites (EP/POSS‐NH₂ 100/0, 95/5, 90/10, and 80/20 wt/wt) were prepared by melt casting and then curing. Viscoelastic and mechanical properties of these composites were studied by dynamic mechanical analysis and mechanical testing, respectively. Scanning electron microscopy was used to study of the micromorphologies of the composites and to elucidate the toughening mechanisms of POSS‐NH₂. POSS units incorporated into the epoxy network showed good compatibility with the resin matrix. Phase separation was not observed even at high POSS content (20 wt%). Incorporation of POSS macromer into the epoxy network after curing increased the glass transition temperature, slightly narrowed the temperature range widths of the glass transition, and lowered the intensities of their loss moduli peaks of the resultant composites. The glass transition temperature of EP/POSS‐NH₂ composites increased significantly with increasing POSS content at lower POSS content (<10 wt%), while increased slightly at higher POSS content. Both impact and flexural strengths of the hybrids reached their optimum values when 10 wt% content of POSS was introduced. POLYM. COMPOS., 28:175–179, 2007. © 2007 Society of Plastics Engineers.     

Energy absorption behaviors of 3D braided composites under impact loadings with frequency domain analysis

This article presented the energy absorption behaviors and damage mechanisms of 3D braided composites under transverse impact and low‐velocity impact with frequency domain analysis method. The transverse impact tests were contracted by modified split Hopkinson pressure bar with the impact velocities of 13.6, 17.8, and 22.8 m/s. The low‐velocity impact tests were performed by Instron 9250 drop‐weight instrument with the impact velocities ranging from 1 to 6 m/s. The experimental results shown that the peak load, displacement to peak load, total energy absorption increased with the increase of impact velocity. The damage morphologies showed the failure mode of 3D braided composite. Increased with the impact velocity, the failure mode changed from resin crack to fiber breakage. The frequency domain analysis results showed that the amplitude of stress wave increased with the increase of impact velocity, but its corresponding frequency was irrelevant to impact velocity. The different amplitude regions corresponded to different failure mode. POLYM. COMPOS., 37:1620–1627, 2016. © 2014 Society of Plastics Engineers     

Behavior of sandwich structures and spaced plates subjected to high‐velocity impacts

This work evaluates the behavior of sandwich and spaced plates subjected to high‐velocity impacts. The sandwich structures were made of glass/polyester face‐sheet and a PVC foam core. The spaced plates were made of two plates of the same material of the sandwich face‐sheet at a distance equal to the core thickness. The residual velocity, the ballistic limit, and the damage area were selected to compare the response of both structures. The residual velocity and ballistic limit was very similar in both cases. Nevertheless, the damage area of sandwich structures and spaced plates differed due to the dissimilar properties between the sandwich core and the air inside of the spaced plates. An analytical model, based on energy criteria, was applied to estimate the residual velocity of the projectile, the absorbed energy by each face‐sheet, and the ballistic limit in the spaced plates. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Preparation and characterization of an epoxy resin modified by a combination of MDI‐based polyurethane and montmorillonite

The present work investigates the modification of epoxy resin by using a combination of nanoclay (montmorillonite—Cloisite 30B) and a liquid polymeric modifier (polyurethane). Polyurethane was obtained from 4,4′‐diphenylmethane diisocyanate and polydiols with different molecular weight: polyethylene glycol (PEG 400) and polyoxypropylene diols with molecular weight 1000 g/mol and 2000 g/mol. The impact strength, the critical stress intensity factor as well as the flexural strength were evaluated as functions of modifiers content. The obtained results showed that hybrid composites exhibit enhanced mechanical properties without significant changes of the glass transition temperature. FTIR analysis showed that chemical reactions took place between the hydroxyl groups of epoxy resin and the isocyanate groups of polyurethane, explaining an improvement of the mechanical properties of epoxy resin. However, XRD results demonstrated the formation of an exfoliated structure for the hybrid compositions with both polyurethane and montmorillonite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011