Increase In Impact Resistance Research Articles

Enhancement of the impact strength of cationically cured cycloaliphatic diepoxide by adding hyperbranched poly(glycidol) partially modified with 10-undecenoyl chains

A hyperbranched poly(glycidol) has been synthesized and modified by acylation with 10-undecenoyl chloride to obtain hyperbranched polymers (HBPs) with different degree of modification. These HBPs have been used as reactive modifiers in a proportion of 3%, 5%, and 10% with respect to a biscicloaliphatic diepoxide cured using ytterbium triflate as thermal cationic initiator. The materials obtained have been characterized and their mechanical properties evaluated. Phase separated materials have been obtained, with a 2-fold increase in impact resistance without sacrificing thermomechanical properties, thermal stability or processability. This good combination of properties can be explained by the achievement of a regular microphase separation with a good interfacial interaction between the microparticles and the epoxy matrix. The compatibility between the HBP and the matrix can be tuned by changing the degree of modification, which leads to a variable amount of available hydroxyl groups of the HBP that can react with the epoxy groups. This chemical bonding occurs through the activated monomer mechanism (AM) which is typical of the cationic homopolymerization of epoxides.

Effect of Zinc Oxide Nanoparticles Concentration on the Mechanical Properties and UV Protection of In Situ Synthesized ABS Based Nanocomposites

AbstractA series of ABS/ZnO nanocomposites with different nanoparticles content were synthesized by mass‐mass and mass‐suspension processes. Because nanocomposites obtained through mass‐suspension process had a greater impact resistance than those derived from mass‐mass process, they were subjected to twin‐screw extrusion. The extrusion led to a dramatic morphological change and increase in impact resistance, higher than 100% in most of the cases. On the other hand, the higher the ZnO content, the higher the UV blocking (>95% for 1 and 3% of ZnO) for both materials, before and after extrusion.

Mechanical, thermal and flame-retardant properties of epoxy–nylon fabric–clay hybrid laminates

Epoxy–nylon fabric laminate composites containing 0.1–0.7 phr clay reinforcements were prepared using a hand layup technique. The fabricated laminates were tested for thermal stability, impact resistance, mechanical properties and flame retardancy. The results indicated an increase in impact resistance, tensile strength, flexural strength and Young’s modulus to an extent and then a decrease as the clay content is increased. Overall results show that a 0.2-phr clay reinforcement into the epoxy–nylon fabric laminate has shown better impact resistance (33.9% more than the neat epoxy–nylon fabric laminate), tensile strength (nearly two times the neat sample), flexural strength (nearly five times the neat sample) and Young’s modulus (39.4% more than the neat sample). Thermal stability is found to decrease slightly upon addition of clay. UL-94 tests conducted on the composite laminate samples have shown a reduction in the burning rate. Also, the tests performed in the present study indicate that the materials under investigation have promising applications in construction, agriculture and decorative purposes.

Effect of Fiber Length on Impact Resistance of Fiber Cement-Based Composites Containing Silica Fume

This study is aimed to evaluate the impact performance of cement-based composites which comprise steel fibers and silica fume in the mixes. Material variables include water-cementitious ratio, dosage of silica fume, steel fiber length and dosage. Test results indicate that the impact resistance increase with increasing fiber content and water-cementitious ratio, and with decreasing silica fume content. For a given volume fraction, short fiber performs better than its long counterpart in improving the impact performance. In addition, the combination of silica fume and fibers enhances better impact behavior than individual constituents of silica fume, due to reduced the crack formation and offer the toughness of cement-based composites under impact loadings.

Efficient impact resistance improvement of epoxy/anhydride thermosets by adding hyperbranched polyesters partially modified with undecenoyl chains

Boltorn H30 hyperbranched polyester has been modified by acylation with 10-undecenoyl chloride to obtain HBPs with different degree of modification. These HBPs have been used as reactive modifiers, in a proportion of 5 and 10%, of DGEBA/MHHPA/BDMA formulations. The materials obtained have been characterized and their mechanical properties evaluated. Depending on the degree of modification of the HBP, homogeneous or phase separated materials were obtained, which influence the properties. When the degree of modification of the HBP was a 76%, a 4-fold increase in impact resistance was achieved without sacrificing thermomechanical characteristics, thermal stability or processability. This has been attributed to the regular microphase separation achieved and to the good interfacial interaction of the microparticles with the epoxy matrix by formation of covalent bonds between the remaining hydroxyl groups at the shell of the HBP and the anhydride as the curing agent.

Impact Resistance of Concrete with Partial Replacements of Sand and Cement by Waste Rubber

Effects of partial replacements of sand by waste crumb rubber and fine rubber, and cement by powder rubber, on the performance of concrete under low velocity impact loading were investigated. Specimens were prepared for 5%, 10% and 20% replacements by volume for both sand and cement. For each case, six beams of 100 mm × 100 mm × 500 mm were subjected to 5.15 kg hammer from 900 mm height. The number of blows of the hammer required to induce the first visible crack and ultimate failure of the beam were recorded. The results are presented in terms of impact energy required for the first crack and ultimate failure. The crumb and fine crumb rubbers increased the impact energy for both first crack and ultimate failure; the increase of impact resistance by crumb rubber was more than that by fine crumb rubber. However, the impact energy for both first crack and ultimate failure increased by the replacement of sand with fine crumb and crumb rubbers until 20%, while this energy increased with cement replacement by powder rubber until 10% replacements and then decreased, but is still higher than that of plain concrete.

An experimental and numerical study on how steel and polypropylene fibers affect the impact resistance in fiber-reinforced concrete

In this paper, impact loading results from numerical simulations of plain concrete (PC) and fiber-reinforced concrete (FRC) are compared with experimental testing data, which were based on a testing procedure recommended by ACI committee 544. Concrete specimens were prepared with two water–cement ratios 0.36 and 0.46. Hooked-end steel fibers with an aspect ratio equal of 80 at 0.5% and 1% volume fractions and polypropylene fibers at 0.2%, 0.3% and 0.5% volume fractions were used. Both the numerical and experimental analysis results indicated that increasing the fiber volume fraction increased the impact resistance of the concrete specimens. The impact resistance increase was greater for normal-strength than that for high-strength concrete. The results also demonstrated that steel fibers are more effective at increasing impact resistance than polypropylene fibers.

Effect of polypropylene molecular weight, hydroxyapatite particle size, and Ringer’s solution on creep and impact behavior of polypropylene-surface treated hydroxyapatite biocomposites

In this study, bovine bone was burnt at 400°C and the resulting ash was heat-treated at 900°C for 90 min to get a white powder. Chemical analysis showed that this white powder was mainly hydroxyapatite (HA). Three different average particle sizes of this powder were produced by milling at three different times. The produced HA was surface treated with a silane coupling agent. Composite samples with 40 vol.% of HA were produced by hot press molding and so mechanical testing was done on the specimens in air and Ringer’s solution. The results of these tests showed that on increasing the molecular weight of polypropylene (PP), creep strain of composites decreases proportionally, and ultimate tensile strength (UTS) and impact resistance increase dramatically. In addition, result of mechanical tests on the soaking specimens in Ringer’s solution showed that Ringer’s solution intensively decreases UTS, creep, and impact properties of PP—HA composite. Furthermore, decreasing HA particle size caused UTS rise, creep strain fall, and impact resistance rise for composites in air condition. Vice versa, in wet condition, decreasing HA particle size caused UTS, creep, and impact resistance to fall. Fracture surfaces of impact samples tests were analyzed by a scanning electron microscope.

Effect of Molecular Weight, Particle Size and Ringer’s Solution on Mechanical Properties of Surface-treated Polypropylene-Hydroxyapatite Biocomposites

Bovine bone is burned at 400°C and the resulting ash is heat treated at 900°C for 90 min in order to obtain a white powder. Chemical analysis shows that this white powder is mainly hydroxyapatite (HA). Three different average particle sizes of this powder are produced by milling at three different times. The produced HA is surface treated with a silane coupling agent. Composite samples with 40% (by volume) of HA are produced by hot press molding, followed by mechanical testing in air and in Ringer’s solution. The results show that by increasing the molecular weight of polypropylene (PP), the creep strain of composites decreases proportionally, and the ultimate tensile strength (UTS) and impact resistance increase dramatically. In addition, the effect of testing in Ringer’s solution is to decrease UTS, creep, and impact properties of PP-HA composites. Furthermore, by decreasing the HA particle size, the creep strain decreases, while the UTS and impact resistance increase for the composites tested in air. Vice versa, in a wet condition decreasing of HA particle size causes UTS, creep, and impact resistance to fall. Fracture surfaces of the samples after impact tests are analyzed by a scanning electron microscope.

Effect of Alumina Trihydrate and Borax on Fire Retardancy and Mechanical Properties of High Density Polyethylene (Hdpe) Compounds

The influence of the inorganic flame retardants, including alumina trihydrate (ATH) and borax (Na2B4O7-10H2O, hydrated sodium tetraborate), on the mechanical properties and flammability of high density polyethylene has been studied. Results showed that an increase in the amount of flame retardant compounds caused a decrease in tensile strength, ultimate strain and impact resistance. Using of ethylene vinyl acetate (EVA) caused an increase in impact resistance compared to other compositions without EVA. Flammability test results showed an improvement in flame retardancy due to using alumina trihydrate and borax. Composite containing EVA and borax showed better flammability properties compared with composite containing EVA and ATH because, EVA as a compatibiliser can increase the stability of the borate component and form a glassy layer on the char, which results in an enhancement in the flammability properties. Furthermore a synergistic effect was observed when alumina trihydrate and borax were incorporated together. The charred layers provided a good thermal and flame barrier. Morphological, rheological and thermal gravimetric analyses studies supported the idea that the improvement in the flame retardancy was due to charred layers formed by the ignition of inorganic flame retardant and polymeric matrix.

Self‐reinforcing isotactic polypropylene prepared using crystallizable solvents

AbstractA new approach to reinforce and toughen isotactic polypropylene (iPP) with improved processability is evaluated. The concept involves using a crystallizable solvent that, at process temperatures melts, is miscible with the polymer thereby reducing its process viscosity. As the polymer cools, the solvent undergoes thermally induced phase separation (TIPS) to produce crystallites that increase the modulus of the solid through reinforcement and promote an increase in impact resistance by mechanisms similar to rubber‐toughened materials. Tetrabromobisphenol‐A (TBBPA) is introduced to iPP that forms a homogeneous mixture at elevated temperature and acts as a processing aid, but undergoes phase separation and subsequent crystallization upon cooling to form rigid particles which, in turn, acts as a toughening agent at room temperature. A phase diagram constructed with Flory‐Huggins solution thermodynamics shows good agreement with the experimental results. The steady state shear viscosity decreases as TBBPA content increases for the mixtures in melt state, indicating improved processability. The decrease in viscosity enhances crystallization rate of iPP significantly, most likely due to increased diffusivity, while the structure of iPP crystals remain unchanged. Tensile tests show that as TBBPA content increases (up to 15 wt %), the yield stress decreases while elongation at break increases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The Effect of Masterbatch Addition on the Mechanical, Thermal, Optical and Surface Properties of Poly(lactic acid)

There has been considerable interest in the use of the biodegradable polymer poly(lactic acid) (PLA) as a replacement for petroleum derived polymers due to ease of processability and its high mechanical strength. Other material properties have however limited its wider application. These include its brittle properties, low impact strength and yellow tint. In an attempt to overcome these drawbacks, PLA was blended with four commercially available additives, commonly known as masterbatches. The effect of the addition of 1.5 wt% of the four masterbatches on the mechanical, thermal, optical and surface properties of the polymer was evaluated. All four masterbatches had a slight negative effect on the tensile strength of PLA (3–5% reduction). There was a four fold increase in impact resistance however with the addition of one of the masterbatches. Differential scanning calorimetry demonstrated that this increase corresponded to a decrease in the polymer crystallinity. However there was an associated increase in polymer haze with the addition of this masterbatch. The clarity of PLA was improved through the addition of an optical brightener masterbatch, but the impact resistance remained low. The glass transition and melting temperatures of PLA were not affected by the addition of the masterbatches, and no change was observed in surface energy. Some delay in PLA degradation, in a PBS degradation medium at 50 °C, was observed due to blending with these masterbatches.

Exfoliation targeted toughness enhancement in polypropylene‐blend‐ montmorillonite nanocomposites

AbstractBACKGROUND: Both exfoliated and toughened polypropylene‐blend‐montmorillonite (PP/MMT) nanocomposites were prepared by melt extrusion in a twin‐screw extruder. Special attention was paid to the enhancement of clay exfoliation and toughness properties of PP by the introduction of a rubber in the form of compatibilizer toughener: ethylene propylene diene‐based rubber grafted with maleic anhydride (EPDM‐g‐MA).RESULTS: The resultant nanocomposites were characterized using X‐ray diffraction, atomic force microscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis and Izod impact testing methods. It was found that the desired exfoliated nanocomposite structure could be achieved for all compatibilizer to organoclay ratios as well as clay loadings. Moreover, a mechanism involving a decreased size of rubber domains surrounded with nanolayers as well as exfoliation of the nanolayers in the PP matrix was found to be responsible for a dramatic increase in impact resistance of the nanocomposites.CONCLUSION: Improved thermal and dynamic mechanical properties of the resultant nanocomposites promise to open the way for highly toughened super PPs via nanocomposite assemblies even with very low degrees of loading. Copyright © 2008 Society of Chemical Industry

Mechanical Properties and Morphology of Ternary PP/EPDM/PE Blends

The ternary blends of high-density polyethylene (PE), EPDM terpolymer and polypropylene (PP) have been used as a model low interfacial tension system to study encapsulation dynamics in ternary blends and their relation to the blends' mechanical properties. It was found that the modulus, tensile strength and impact resistance can be improved by PE addition if the PE is localized within the EPDM phase. A range of blend morphology was found depending on the PE viscosity and polymer incorporation sequence in the twin-screw extruder. In the most favorable sequence, PE and EPDM were mixed together prior to their dispersion in the PP matrix. This practice resulted in a 50% increase in impact resistance when compared to mixing the three components in a single-step.

Toughening of Epoxy Resin by Methyl Methacrylate/2‐Ethylhexyl Acrylate Copolymers: The Effect of Copolymer Composition

AbstractMMA‐EHA copolymers with different compositions and with a low amount of AA were synthesized and used as impact modifier for epoxy networks. The effect of the copolymers on the tensile and dynamic mechanical properties as well as impact resistance of the epoxy network was evaluated. The addition of 10 phr of low‐molar‐mass MMA‐EHA copolymer with defined composition resulted in a significant increase in impact resistance without any significant changes in the tensile strength, modulus, and glass transition temperature. The morphology of the modified epoxy network depends upon the copolymer composition.magnified image

Study of Polyamide 1212/Polyamide 6 Composites with Microfiber Structure via in-Situ Anionic Polymerization

A series of novel PA 1212/PA 6 composites were synthesized via in-situ polymerization. Incorporating minor PA 1212 (2−12 wt %) into PA 6 matrix led to about 5 times increase of impact resistance of PA6 with its tensile strength maintenance. Inserting PA 1212 macromolecules into PA 6 matrix by this method may interfere with the arranging order of hydrogen bonding of PA 6 by changing its crystalline structure and impeding its crystallization. Different from the homogeneous molecular PA 66/PA 6 composites, PA 1212/PA 6 composites had a microfiber structure with width 100−300 nm and length several micrometers. PA 1212/PA 6 composites had better crystalline thermal stability and comprehensive mechanical properties than the corresponding molecular PA 66/PA 6. After tensile deformation, the lamellar bundles in PA 1212/PA 6 had a prior orientation along the tensile direction, while the orientation direction in pure PA 6 had an angle about 45° with the tensile direction. The crystalline microstructure and morphology of PA 1212/PA 6, especially the microfibers, might play an important role in the toughening of PA 6 with maintenance of strength.

Mechanical and thermal properties of toughened polypropylene composites

AbstractThe mechanical, thermal, and structural properties of a new flexible composite containing polypropylene fiber (PP) in a random poly(propylene‐co‐ethylene) (PPE) matrix with ethylene–propylene elastomer (EP) was investigated with emphasis on the effect of EP elastomer concentration. The intrinsic composition of the composites, toughening of the matrix with EP and the fiber–matrix interface determined the properties of the composites. Through the incorporation of EP elastomer into the polypropylene–poly (propylene‐co‐ethylene) (all‐PP) composite, tensile and storage modulus (E′) decreased, flexural modulus and loss modulus (E″, damping) increased slightly to 0.15 EP and then decreased. There was an increase in impact resistance for the toughened composites, with about 100% increase in comparison with an untoughened all‐PP composite. The composition corresponding to 0.20 weight fraction EP gave optimum impact and mechanical properties. Creep resistance of the composite decreased with increasing EP content, but recovery showed an increase with increasing EP content up to 0.20. Fracture surfaces of composites after impact tests were studied with scanning electron microscopy. Moreover, the use and limitation of theoretical equations to predict the tensile and flexural modulus of the flexible PP composite is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Hydroxy‐terminated polybutadiene toughened epoxy resin: Chemical modification, microstructure, and impact strength

AbstractThe toughening of the epoxy resin diglycidyl ether of bisphenol A with hydroxy‐terminated polybutadiene (HTPB) was investigated. A chemical link between the elastomer and the epoxy resin was promoted employing tolylene diisocyanate (TDI). In the first step, HTPB and TDI (in excess) reacted forming urethane links, and after increasing the temperature and adding a catalyst, TDI–HTPB reacted with epoxy resin forming oxazolidone links. The reactions were followed by FTIR and chemical analysis. The final cured materials contained up to 10 phr of elastomer. Impact resistance increased with elastomer concentration up to 5 phr of HTPB, which was present as rubber particles with average diameter ranging from 1 to 4 μm. Higher concentrations of HTPB resulted in larger particles and gave lower impact values. The overall results have shown that it is possible to obtain, with the process employed, an impact resistance increase of 100% with the use of HTPB as a toughening agent for the epoxy resin. © 2002 John Wiley & Sons, Inc. Adv Polym Techn 21: 25–32, 2002; DOI 10.1002/adv.10012

Mechanical properties of internally nitrided Fe−Ti and Fe−Cb alloys

Highly formable ferrous alloys containing Ti or Cb can be strengthened by a nitrogenation treatment which produces alloys containing dispersions of submicroscopic particles of TiN or CbN. By this treatment, the yield strength of alloys containing only 0.2 pct Ti or 0.3 pct Cb is increased from 105 to 700 MPa while retaining tensile elongations of 10 to 15 pct, good bendability, and good impact resistance. The CbN particles begin to coarsen at 600°C causing softening, a decrease in electrical resistivity, and an increase in impact resistance. The first response to annealing of the Fe−TiN system is a drop in resistivity which also begins at 600°C. Attending this change is an increase in hardness which continues to 800°C where the first precipitates become discernible by transmission electron microscopy. Subsequently, hardness falls as the particles grow to discs on {100} planes. The magnitude of the strengthening, its concentration dependence, and its response to heat treatment are adequately explained by a model which attributes initial resistance to dislocation motion to coherency strains set up by a distribution of very fine precipitates. With particle growth, strengthening first increases until at a critical particle size Orowan looping becomes dominant; thereafter softening occurs with further growth.