Comparative mechanical property characterization of three indirect composite resin materials compared with two direct composites

Various new indirect composite materials have been developed with required advantages. In this study three indirect composite material (Artglass, Belleglass HP, Targis) were tested for flexural strength, fracture toughness, wear resistance and hardness against Filtek P60 and Z‐100. Five specimens of each material were fabricated according to the manufacturer's directions. The flexural strength and fracture toughness was measured using the bending test. The wear test was performed to accelerated wear in a toothbrushing apparatus. Vickers hardness was measured for each of the tested materials. The statistical tests used for flexural strength, fracture toughness, wear and hardness were One‐way ANOVA and Kruskal–Wallis test. The level of statistical significance chosen was p = 0.05. Results of the study showed that Filtek P60 was superior to the other composites in all tests. Significant differences were found among the materials. The differences in flexural strength, fracture toughnes, wear and hardness may have been due to differences in chemistry or method of polymerization of the composites. Copyright © 2003 John Wiley & Sons, Ltd.     

Changes in the mechanical properties of tooth-colored direct restorative materials in relation to time

The objective of this study was to determine the flexural strength, flexural modulus, Vickers hardness of a packable composite (Surefil), and an ormocer (Definite) in comparison with a microhybrid composite (Z-100), a microfil composite (Silux Plus) and a polyacid-modified composite resin (Dyract). Flexural strength and flexural modulus were determined using a three-point bending device. Microhardness was measured with a Vickers indentor. The specimens of each material were prepared according to manufacturer's instructions. The specimens were stored in artificial saliva at pH 6, all at 37°C. The groups were tested at the beginning of the test, at 3 months and at 6 months. Flexural strength values of Surefil and Definite showed a progressive increase. The highest MPa values were determined for Surefil (134.4 MPa) and the lowest MPa values were obtained for Dyract (59.6 MPa). The highest flexural modulus values were revealed for Surefil (10.000 GPa). Z-100, Silux Plus and Definite showed a tendency to decline in relation to time for their flexural modulus. GPa values of Silux Plus were stable at 3 and 6 months. Vickers hardness numbers showed that Surefil was the hardest and Dyract was the weakest material. Copyright © 2003 John Wiley & Sons, Ltd.     

X-ray diffraction and X-ray photoelectron spectroscopy studies of Ni-P deposited onto carbon fiber surfaces: impact properties of a carbon-fiber-reinforced matrix

In this work, the Ni-P coating on carbon fiber surfaces was carried out in order to improve the impact resistance of carbon fibers-reinforced epoxy matrix composites. The fiber surfaces and the fracture behaviors of composites were measured in terms of X-ray diffraction spectrometry (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), and falling weight impact testing. From the XRD and XPS measurements, it was observed that Ni-P coating of carbon fibers led to an increase in two phases, i.e., microcrystalline and amorphous, mainly due to the increase of NiP(2), Ni(3)P, and Ni metal. Energy adsorbed by composites through the various fracture mechanisms was seen to be the characteristic distinguishing between nontreated and treated fiber-reinforced composite systems. The Ni-P alloy technique to improve the impact resistance of the composites was shown to be the modification of fiber-epoxy resin interfaces.     

The interactions of tooth colored dental restorative materials with aqueous lactic acid

In this study, the interaction of packable composite and ormocer with aqueous lactic acid solutions were determined and changes compared with those for a polyacid modified resin composite and a glass ionomer. For each material, namely Solitaire, Z‐100, Definite, Dyract AP and Vitremer, eight cylindrical specimens of 6 mm diameter and 12 mm height were prepared and weighed. They were stored individually in 20 cm³ 0.02 mol^?1 lactic acid solution for 1 week, then the pH was determined and the specimens reweighed. This was repeated at 1 week intervals until the specimens were 6 weeks old. The results of this study showed that; polyacid modified resin composites and resin‐modified glass‐ionomers were capable of increasing the pH of lactic acid solutions. The same groups showed an increase in mass during the first week. Composite resins and ormocer showed less increase in mass than the others. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis, crystal structures, and optical properties of two new layered quaternary tantalum thiophosphates and the thermal conversion of Cs4Ta4P4S24 into Cs2Ta2P2S12

The reaction of Ta with an in situ formed polythiophosphate melt of Cs2S3, P2S5, and S yields the two new quaternary tantalum thiophosphates Cs2Ta2P2S12 (I) and Cs4Ta4P4S24 (II). Both compounds were obtained with the same stoichiometric ratio but at different reaction temperatures. Compound I was prepared at 873 K and crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 8.862(2) A, b = 12.500(3) A, c = 17.408(4) A, beta = 99.23(3) degrees, and Z = 4. Compound II was prepared at 773 K and crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 14.298(3) A, b = 17.730(4) A, c = 16.058(3) A, beta = 106.19(3) degrees, and Z = 4. The two structures are closely related and exhibit two-dimensional anionic layers consisting of dimeric [Ta2S11] units which are linked by two tetradentate and two tridentate [PS4] tetrahedra. The significant difference between these two compounds is the orientation of the [Ta2S11] units in infinite [Ta2S4(PS4)]x chains which are subunits of both structures. The specific orientation of the [Ta2S11] blocks in compound I leads to the formation of one cavity in the 2(infinity)[Ta2P2S12]2- layers, whereas in compound II two types of cavities are observed in the 2(infinity)[Ta4P4S24]4- layers. The Cs+ ions are located between the layers above and below the cavities. The compounds were characterized with infrared spectroscopy in the MIR region, Raman spectroscopy, and UV/Vis diffuse reflectance spectroscopy. When Cs4Ta4P4S24 (II) is heated at the synthesis temperature of compound I it is fully converted into compound I.     

Accelerated weathering of polypropylene/wood flour composites

Wood-plastic composites (WPCs) have received increasing attention during the last decades, because of many advantages related to their use. Some of their main applications are represented by outdoor furnishing and decking; therefore, it is important to assess their behaviour under UV exposure. In this work, polypropylene/wood flour composites were prepared and their resistance to photooxidation investigated. The composites were prepared by extrusion and compression moulding, and were subjected to mechanical tests, FTIR analysis and molecular weight measurements. The results showed that the composites retained a higher fraction of the original mechanical properties after accelerated weathering; the wood flour did not significantly degrade throughout the irradiation time slot of the investigation and the composites kept a higher percentage of the original molecular weight.     

PE-CPE blends and their graphene oxide nanocomposites with reduced low temperature brittleness

The low-temperature flexibility of polyethylene (PE)–chlorinated polyethylene (CPE) blends and their composites with a small amount of graphene oxide filler was studied. Quantitative height variation in the AFM images, rheological as well as fracture analyses were employed to gain insights into the generation of flexibility in the matrix phase. The semi-crystalline CPE (CPE25) polymer did not induce viscoelastic behavior at temperatures lower than the glass transition temperature of PE, whereas the amorphous CPE (CPE35) had completely different behavior. The samples with CPE35 could not be sufficiently hardened even at ?180 °C and remained too soft for cryosectioning. Therefore, compression, which results in a 30–60 % reduction in length along the cutting direction with no change in the dimension perpendicular to it, was very prominent for both thin section and block face of the sample. The composites had even higher degree of compression due to additional effect of weak filler matrix interactions and as a consequence, the topographical variations led to filler pull out during sectioning. It was also confirmed using the rheological analysis that composites (and blends with 10 % CPE35 content) had phase immiscibility as CPE phase was suspected to concentrate near the graphene oxide phase leading to generation of chlorine-rich phases. The addition of graphene oxide did not lead to reduced flexibility and the composites also retained the modulus similar to pure polymer. The mechanical fracture of the samples also confirmed the flexibility of the CPE containing blends and composites as these samples were still flexible at ?195 °C.     

纳米级金红石型二氧化钛与受阻胺光稳定剂协同改进ABS的抗老化性能研究

分别采用纳米级金红石型TiO2和受阻胺光稳定剂(HALS)对ABS进行改性,通过熔融共混法制备了ABS/纳米TiO2、ABS/纳米TiO2/HALS和ABS/HALS复合材料,采用GB/T16422.2~1999所述的塑料实验室光源暴露实验方法,用氙灯气候试验机对其进行28天人工加速老化,通过测定其老化过程中的无缺口和缺口试样冲击强度的变化来对其抗老化性能进行表征,同时利用光学显微镜和扫描电镜对其老化过程中的冲击断口形貌变化进行了研究.结果表明,纳米TiO2在ABS基体中分散良好,改性后的复合材料均具有较好的抗老化性能,纳米TiO2与HALS复合改性ABS对其耐候性的提高具有明显的协同作用,其老化后的抗冲击性能超过了单一使用HALS或纳米TiO2的改性效果,老化28天后纯ABS树脂试样的无缺口冲击强度保持率只有20%左右,添加2.0 wt%纳米TiO2后,老化28天后的ABS/纳米TiO2/HALS复合材料试样的保持率则提高到47.9%,为纯ABS树脂试样的2.5倍.     

Optimization of scratch resistance and mechanical properties in wollastonite‐reinforced polypropylene copolymers

The aim of this research was to establish a balance between scratch resistance and scratch damage visibility in the wollastonite‐filled heterophasic polypropylene copolymers.The influences of various factors including the surface hardness, elasticity, friction coefficient, and combinations thereof on the scratch behavior (scratch resistance and scratch visibility) were elucidated. Using micro‐scale and nano‐scale scratch tests and image analysis techniques, the scratch hardness, scratch depth, and scratch visibility of the composites were characterized.It was found that the introduction of wollastonite in the polypropylene copolymer matrix contributes to ductile fracture behavior because of an induced crystallization alteration. Accordingly, the scratch resistance of reinforced composites revealed an increase as a result of higher stiffness of the wollastonite as well as contribution of new crystalline structure. The addition of siloxane to the composites improved the resistance to surface damage by lowering the surface friction coefficient originated from enhanced chain mobility. Simultaneous addition of high density polyethylene and siloxane induced a significant influence on the resistance to the scratch damage. Copyright © 2015 John Wiley & Sons, Ltd.     

Monomeric and polymeric dinuclear complexes of Co(II) or Ni(II) with calix[4]arene-tetraphosphineoxide

Monomeric and polymeric 1:2 complexes of a novel calix[4]arene-tetraphosphineoxide with Co(II) or Ni(II) nitrates were synthesized and analyzed by the X-ray method. In the monomeric complexes each metal cation is coordinated by two bidentate NO₃-ligands as well as by two proximal P=O groups at the calixarene skeleton. In the nickel metallopolymer one sort of the cations is bound by the two proximal P=O-groups but other cations link neighboring calixarene molecules through Р=О···Ni···O=P chains. The complexes possess molecular cavities or channels filled by solvent molecules. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The use of zinc dimethacrylate functionalized graphene as a reinforcement in rubber composites

Zinc dimethacrylate functionalized graphene (Z‐GE), as reinforcing nanofiller for natural rubber (NR), was synthesized by liquid‐phase exfoliation and in situ method. The morphology and structure of Z‐GE were characterized to confirm the exfoliation and functionalization of GE. The NR/Z‐GE composites were prepared and investigated by mechanical analysis, crosslinked network analysis and the analysis of thermal conductivity. The results showed that the tensile strength, tear strength and modulus at 300% strain of NR/Z‐GE‐20 composites (contents 1.400 phr GE) were increased by 142%, 76% and 231% as compared with the pure NR, respectively. And the thermal conductivity of NR/Z‐GE‐30 composites is enhanced by 39% as that of the pure NR. This significant improvement is attributed to the formation of covalent crosslinked network and ionic crosslinked network and efficient interfacial interaction between GE and NR matrix. This method provides a new insight into the fabrication of multifunctional GE composites and enlarges its potential applications in high performance GE‐based rubber composites. Copyright © 2015 John Wiley & Sons, Ltd.     

Kinetics of anhydride formation in poly(acrylic acid) and its effect on the properties of a PAA-alumina composite

The kinetics of anhydride formation of poly(acrylic acid) (PAA) in porous PAA–alumina composites have been investigated by using a thermogravimetric technique (TGA). Three distinct reaction peaks at 200°C (I), 250°C (II), and 390°C (III) were identified in the dynamic TGA thermogram. These peaks were attributed to bound water removal (I), anhydride formation (II), and polymer degradation (III). The kinetics of the anhydride reaction were studied in a temperature range of 220–240°C and found to follow a second-order mechanism with an activation energy of approximately 38 kcal/mole. In addition, the bound water was found to inhibit the onset of anhydride formation. The degree of conversion to anhydride was correlated with the equilibrium swelling level attained by the composite in water.     

Influences of Plasma Treatment and 60Co γ-Ray Radiation on the Over-Voltage Positive Temperature Coefficient of High Density Polyethylene/Carbon Black Nano Composites

Argon plasma-pretreated high-density polyethylene (PHDPE) was blended with the conductive nano carbon black (CB) and inorganic flame retardant (magnesium hydroxide, Mg(OH)₂) was added. Influences of the CB content, plasma treatment time, plasma treatment power, and dosage of ⁶⁰Co γ-ray radiation on positive temperature coefficient (PTC) behaviors of composite were studied. In addition, the over-voltage resistance behavior of the composites was also investigated. The free radical of PHDPE was measured by 1,1-diphenyl-2-picryhydrazyl (DPPH) method. The gel contents of composite were measured by solvent extraction method. The results showed that the room-temperature volume resistivity and PTC effect of composite were improved significantly with plasma treatment. The PHDPE composite with ⁶⁰Co γ-ray radiation eliminated the negative temperature coefficient (NTC) effect in the composites effectively, and the PTC intensity of composite was increased. With increasing of radiation dosage from 20 Mrads to 80 Mrads, the gel content of composites increased up to 83.84% and the response temperature of composites shifted to low temperature (127.5 °C to 114.8 °C). In this work, the composites also successfully passed the over-voltage resistance test, and possessed good reproducibility.     

Synthesis and characterization of ReO4-containing microporous and open framework structures

A microporous and an open framework structure, [Cu(2)(pzc)(2)(H(2)O)(2)ReO(4)] (I) and [Cu(pzc)(H(2)O)ReO(4)].2H(2)O (II) (pzc = 2-pyrazinecarboxylate), respectively, have been prepared using hydrothermal methods and characterized using IR, TGA, and X-ray diffraction (I Pnma, No. 62, Z = 4, a = 7.4949(9) A, b = 24.975(3) A, c = 9.141(1) A; II P2(1)/c, No. 14, Z = 4, a = 8.5878(9) A, b = 12.920(1) A, c = 9.741(1) A, beta = 92.830(2) degrees ). I and II crystallize as red and blue solids, respectively, and each contains chains constructed from alternating Cu(pzc)(2)/ReO(4) oxide-bridged metal sites. The bidentate pzc ligand further bridges each -Cu-O-Re-O- chain to adjacent chains, via the Cu sites, to form a 3D net in I, with ellipsoidal channels that are approximately 3.3-4.7 A x 12.5 A, and in II, stacked layers of square nets with H(2)O-filled cavities that are approximately 4.4 x 5.1 A. Local ReO(4)(-) groups, a component of common oxidation catalysts, are directed at the channels and cavities of each structure, respectively. Thermogravimetric analysis indicates that I loses up to 64% of its H(2)O content before decomposition at 225 degrees C, while II loses approximately 100% of its H(2)O content by 265 degrees C.     

Fabrication and characterization of gamma-irradiated recycled (thermoplastic/elastomer) matrix filled with feldspar composites

A composite of waste polyethylene, recycled waste rubber powder and reactive compatibilizing agent maleic anhydride, 60/40/2 mass%, was loaded with increasing contents, up to 20 mass%, of the reinforcing filler, feldspar [K (Al SiO₃O₈)]. The composites were gamma-irradiated at various doses up to 150 kGy. Selected physical, mechanical, and thermal parameters were investigated as functions of radiation dose and filler content. Gamma irradiation led to a significant improvement in the properties for all composites irradiated with 150 kGy. Similarly, the increase in feldspar content provided substantial improvement in properties as a result of development in the interfacial adhesion between the filler particles and composite components. The results were confirmed by examining the fracture surfaces using scanning electron microscopic techniques.     

Insect pheromones and their analogues. XVIII. Regiospecific synthesis of (±)-15,19-dimethyltritriacontane — A component of the pheromone of Stomoxys calcitrans

(±)-15,19-Dimethyltritriacontane (II) — a component of the pheromone of the stable fly — has been obtained by a five-stage synthesis from dimethylcyclooctadiene (I). The coupling of 1,1-dimethoxy-4-methyl-8-oxonon-4Z-ene [the product of the ozonolysis of (I)] with n-C₁₃H₂₇CH=PPh₃ (THF; ?30°, 2 h; 25°, 15 h; Ar) gave 1,1-dimethoxy-4,8-dimethyldocosa-4Z,8Z(E)-diene (III). The hydrolysis of (III) (TsOH·Py, H₂O-Ac, boiling, 4 h) gave the corresponding aldehyde (IV). The condensation of (IV) with n-C₁₀H₂₁CH=PPh₃ (THF; ?60° to ?30°C, 2 h, 25°C, 15 h) led to 15,19-dimethyltritriaconta-11Z(E),15Z,19Z(E)-triene (V), the exhaustive hydrogenation of which (ethanol, H₂, 5% Pd/C, 25°C) gave (II). The substance, the yield in %, and R_f values are given, respectively: (II), 95, 0.92; (III), 29, 0.74; (IV), 80, 0.72; (V) 50, 0.8. The IR and PMR spectra of compounds (II)–(V) and the mass spectra of (II) and (III) are given.     

Dynamic flexibility of a peptide-binding groove of human HLA-DR1 class II MHC molecules: normal mode analysis of the antigen peptide-class II MHC complex

Class II major histocompatibility complex (MHC) has tolerance for binding longer antigen peptides than those bound by class I MHC. In this paper, a normal mode analysis on HLA-DR1 class II MHC involving an antigen peptide indicated that the peptide-binding groove had some different dynamic characteristics from that of HLA-A2 class I MHC. The dynamic changes in the class I groove with removal of the bound peptide were limited primarily to the central region and the C-terminal side (corresponding to the C-terminal side of the bound peptide) of the groove, while the dynamic changes in the class II groove with removal of the bound peptide extended to the whole of the groove, and were especially remarkable around a strand located in the N-terminal side (corresponding to the N-terminal side of the bound peptide) of the groove. These results suggest that the N-terminal side of the class II groove is more flexible than the same side of the class I groove, and this flexibility may allow some N-terminal residues of the bound peptide to extend outside the class II groove. Definite anti-correlative motions with removal of the bound peptide appeared between two alpha-helical regions of class II MHC as in the case of class I MHC. These motions of the class II groove may play an important role in obtaining "a flexible dynamic fit" against diverse longer peptides both of whose terminals extend outside the groove.     

Interlaminar Fracture Toughness of Carbon Fiber/Epoxy Composites using Short Kevlar Fiber and/or Nylon-6 Powder Reinforcement

Mode I (G_IC) and Mode II (G_IIC) interlaminar fracture toughness of carbon-fiber/epoxy composites have been investigated as a function of the amount of short Kevlar-29 fiber (SKF) and/or Nylon-6 powder (N6P) between continuous fiber layers. G_IIC increased with increasing crack length as a consequence of the presence of SKFs bridging in the wake of propagating crack. G_IIC of SKF alone could reach the maximum at an intermediate amount of SKF. G_IIC of SKF and N6P was lower than that of SKF alone because N6P prevented the orientation of SKF to out-of-plane. The extent of SKF's bridging phenomenon may be influenced by the amount and orientation of SKF. G_IC showed no significant effect with SKF and uniform irrespective of crack length. Scanning electron microscopy after G_IIC test showed that new surfaces were created by extensive fiber bridging, pull-out and fracture of SKF in random direction without any fixed pattern. © 1997 John Wiley & Sons, Ltd.     

Designing semiencapsulation based covalently self‐healable poly(methyl methacrylate) composites by Atom Transfer Radical Polymerization

Self‐healable poly(methyl methacrylate) (PMMA) composites were fabricated with embedded glycidyl methacrylate (GMA) encapsulated poly(melamine‐formaldehyde) microcapsules. The matrix polymers were synthesized via Atom Transfer Radical Polymerization using two different initiators; one linear and another hexafunctional. As the so prepared polymer matrix retains living characteristics, it can initiate a healing reaction when the encapsulated monomer reaches the matrix due to formation or extension of a crack and thus healing the system covalently. The effect of number of initiating functionality on healing characteristic was studied using both linear and 6‐armed star PMMA having same targeted molecular weight. Both the systems were able to restore 100% original fracture toughness after healing. However, the polymer matrix prepared by hexafunctional initiator restored the fracture toughness much faster than that of the linear polymer matrix. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1842–1851     

Composites supraconducteurs “oxyde / oxyde”: Conditions de frittage et propriétés électriques de composites Bi-2212 / isolant

In order to improve the electrical and/or mechanical properties of bismuth cuprate superconductors, composites have been elaborated by pressing polycrystalline Bi₂Sr₂CaCu₂O_{8 + δ} (2212) mixed with two insulator oxides into pellets, which were sintered near 800 °C. A large domain of composition was investigated. The Bi₂CuO₄ (2001) oxide reacts with the Bi-2212, decreases its T_c value but can increase its mechanical resistance. The Bi₂Sr₃CaO₇ (2310) oxide seems not to react with the 2212. A zero resistance at low temperature (> 40K) is observed up to 30 vol.% of superconductor oxide (20 vol.% taking into account the insulating cavities) in the 2310/2212 composites.