Improvement of interfacial adhesion between wood and polypropylene in wood–polypropylene composites

N-vinylformamide-grafted polypropylene (VFPP) was successfully synthesized through a free radical grafting reaction. Both polymeric methylene diphenyl diisocyanate (PMDI) and VFPP were effective compatibilizers for increasing both the strength and stiffness of the resulting wood–PP (polypropylene) composites. Both the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the resulting wood–PP composites were further increased when PMDI and VFPP were used together as an integrated compatibilizer system. This new PMDI-VFPP compatibilizer system was comparable to maleic-anhydride-grafted polypropylene in terms of enhancing the strength and stiffness of the wood–PP composites. Study of the fractured surfaces of the wood–PP composites with scanning electron microscopy revealed that this new PMDI-VFPP compatibilizer system greatly improved the interfacial adhesion between wood and PP. This PMDI-VFPP compatibilizer system also greatly reduced the water absorption of the resulting wood–PP composites. In this PMDI-VFPP compatibilizer system, PMDI is proposed to function as a wood-binding domain and VFPP to function as a PP-binding domain. PMDI reacted with the amide group in VFPP, thus forming covalent linkages between PMDI and VFPP.     

Preparation and characterization of wood-fiber-reinforced polyamide 6–polypropylene blend composites

In this study, we used lithium chloride (LiCl) as a modifier to decrease the melting temperature (T _m) of polyamide 6 (PA6), and then, we fabricated wood-fiber-reinforced PA6–polypropylene (PP) blend composites via hot pressing. From crystallization analysis, the composites exhibited a lower T _m and a lower processing temperature compared to PA6. Color and Fourier transform infrared analyses showed that severe thermal degradation and discoloration of the composites could be prevented by the incorporation of LiCl. LiCl had positive effects on the mechanical properties of the final product and the interfacial compatibility among PA6, PP, and wood fiber. The flexural strength increased by 8.5%. In addition, both maleic anhydride grafted PP and wood fiber improved the mechanical properties. The flexural strengths increased by 7.9 and 40%, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47413.     

Microstructure evolution and phase transformation of amorphous BCN–SiC composites prepared by two synthetic routes

Two amorphous BCN–SiC composites, sample BSC (BN + SiC + C) and sample BCSA (B₂O₃+C + Si + AlN) were prepared from different raw materials via spark plasma sintering (SPS) for 5 min at 1670 °C under a pressure of 30 MPa. Sample BCSA was found to generally outperform sample BSC, and its relative density (99.13% vs. 97.28%), flexural strength (453.1 MPa vs. 334.5 MPa), Vickers’ hardness (19.15 GPa vs. 16.53 GPa), and fracture toughness (5.21 MPa m^1/2 vs. 3.76 MPa m^1/2). The solid-phase reactions in the binary (sample BSC) and quaternary (sample BCSA) systems were elucidated from X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and thermodynamic calculations. The microstructure of the composites, which were synthesized from two different materials, was also characterized. The grain size and aspect ratio of the lamellar amorphous BCN grains played an important role in improving the mechanical properties of the composites. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) were used to clarify the microstructure of the amorphous phase of BCN and its interfacial area. Based on these results, element diffusion was discussed. The mechanism for the microstructural evolution and phase transformation of the composite were also discussed.     

Design of new polypropylene–woodflour composites: Processing and physical characterization

Woodflour/polypropylene composites were prepared with 10 and 20% in weight of woodflour (WF). The influence of the WF, the compatibilizer, and processing aid (WP) in the crystalline structure of the polypropylene was studied by thermal analysis. The results showed that the WF acts as a nucleating agent, increasing the crystallization rate of the PP at the cooling rates studied. The morphological study by SEM proved that the WP increased the dispersion of the filler into the PP matrix, and the ionomer, used like compatibilized improved the adhesion between the PP and the filler obtaining a more uniform morphology. The mechanical properties indicated that the incorporation of the ionomer and the WP enhanced the ductility of the composites at the same time that the materials reached a more uniform morphology. The amount of additives (compatibilizer and WP) included in the woodflour-plastic composite (WPC) formulations was small, for this, the formulations are suitable to use in a possible industrial application. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Fabrication and properties of cordierite based glass/AlN composites by sol–gel and pressureless sintering

In this study, the effect of AlN content on the crystallization behavior of cordierite based glass, was firstly investigated. Results show that μ-cordierite appeared in the composites with high AlN content even at high temperatures, which implied that the AlN may broad the crystallization temperature range of μ-cordierite and depress the transformation of μ→α-cordierite. The crystallization temperature of α-cordierite was about 980 °C for the pure glass and the temperature increased with AlN content for composites, but the crystallization temperature of μ-cordierite had reverse trend. The composites owned excellent bending strength when the AlN content was 20 wt%. With increasing of AlN content, the dielectric loss was increased which was caused mainly by the structural loss and the appearance of μ-cordierite, but the dielectric constant had crosscurrent. It was observed that the composites were beneficial in producing LTCC material which can be highlighted with high strength, low shrinkage and good dielectric properties at 1 MHz.     

Sintering and thermal expansion behaviors of glass and glass–YSZ composites as self-repairable seals for SOFC

Glass and glass–ceramics are used as sealants in solid oxide fuel cell (SOFC) because their thermophysical properties can be tailored to meet the stringent requirements of the SOFC stack. The processing, sintering, and thermal expansion behaviors of self-healing and non-crystallizing glass and glass containing 10%–30 wt.% non-reacting yttria-stabilized zirconia (YSZ) are studied. The addition of inert YSZ to glass significantly retarded the sintering behavior. Thermal expansion behaviors of glass and glass–YSZ are also measured to study the role of YSZ addition on the glass transition, softening point, and coefficient of thermal expansion (CTE). It is shown that the densification is controlled by the viscous sintering mechanism, in which the addition of YSZ increased the effective viscosity of the glass–YSZ as evident from higher glass transition and softening temperatures and decreased CTE. These results demonstrated that the addition of YSZ to glass is promising for achieving optimum thermophysical properties useful as seals for SOFC.     

Effects of vinyltrimethoxy silane on thermal properties and dynamic mechanical properties of polypropylene–wood flour composites

The viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pretreatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of organosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP-nucleating agent, increasing the PP crystallization rate. In general, pretreatment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical properties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Theoretical study of the thermal conductivity of silica glass–crystal composites

The heat dissipation of silicate glasses draws much attention for various applications, and the desire for glasses with high thermal conductivity remains an unsolved challenge. The structural origin of thermal conductivity in glass remains not fully understood. The present study aims to elucidate the impact of embedding highly thermally conductive crystalline α-quartz in a silica glass matrix. We consider both nano-thread (NT) (1D) and nano-plate (NP) (2D) structures and use molecular dynamics simulations to evaluate the role of its connectivity on thermal conductivity in the glass–crystal composite as a function of the volume fraction of the α-quartz region. The directional dependence of thermal conductivity was also investigated to obtain percolation threshold behavior along the cross-sectional directions, whereas the parallel circuit model of electricity can be used to account for the change of thermal conductivity along the longitudinal direction. Incorporation of α-quartz NTs or NPs into silica glass offers the opportunity to enhance its thermal conductivity.     

Mullite–zirconia–zircon composites: Properties and thermal shock resistance

In the refractory field mullite and zirconia are the basis of materials used in the glass industry or when high chemical stability and corrosion resistance are necessary. In this work various mullite–zirconia/zircon compositions were investigated to improve the thermal shock (TS) resistance of dense composites produced by slip casting and sintering at 1600 °C. Zircon (SiZrO₄) acts as bonding phase and its thermal decomposition adds zirconia and silica to the material. Resultant composites were characterized by density and dilatometric measurements, XRD and SEM techniques. TS behavior was tested by quenching in water with quenching temperature differentials ΔT from 400 to 1200 °C. The degree of damage after the TS was experimentally evaluated through the variation of the elastic modulus E which is measured by the excitation technique. The severity of the TS test and the effect of the number of thermal cycles on E for each ΔT employed were determined.The tested materials retained their original mechanical properties for temperatures below a critical temperature ΔT_c near 600 °C. Materials quenched from ΔT of 1000 °C showed as much as 30% reduction in E indicating the important microstructure damage. The TS resistance improved with increasing zircon addition to 35 wt% in agreement with the behavior predicted from R parameter for crack initiation.     

Functional properties of glass–ceramic composites containing industrial inorganic waste and evaluation of their biological compatibility

A study has been carried out on the feasibility of using Latvian industrial waste (peat cool ash, fly ash, aluminium scrap metal processing waste, metallurgical slag and waste cullet glass) and raw mineral materials (limeless clay) to produce dense, frost resistant, chemically durable glass–ceramic materials by powder technology. Highly crystalline and dense products (density: 2.50–2.94 g/cm³, water uptake: 1.3–4.3%) were fabricated from different mixtures by sintering at temperatures in the range of 1060–1160 °C. Glass–ceramics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and four point bending strength test. Chemical durability, soluble salt crystallization as well as biological tests were carried out in order to evaluate the environmental stability and possible toxicity of the materials. The novel glass–ceramics developed here can find applications as building materials, such as wall tiles and for manufacturing industrial floors.     

Surface modification of magnesium hydroxide and its application in flame-retardant oil-extended styrene–ethylene–butadiene–styrene/polypropylene composites

Magnesium hydroxide (MH) was modified with triethoxysilane and polymethyl–vinyl silicone rubber and used to prepare flame-retardant oil-extended styrene–ethylene–butadiene–styrene (O-SEBS)–polypropylene (PP) composites. The water contact angle of modified magnesium hydroxide (MMH) reached 141°; this indicated that MMH possessed excellent hydrophobic properties. The samples (1.6 mm) passed the UL-94 V-0 rating during vertical burning tests when the loading amount of MH or MMH was 70 wt %. This indicated the modification did not decrease the flame-retardant properties of MH. The tensile strength and elongation at break values of the MMH–O-SEBS–PP composites increased by 20.4 and 88.9%, respectively, compared with those of the MH–O-SEBS–PP composites. The modification of MH enhanced the interfacial compatibility between the flame retardant and the matrix; thus, the mechanical performance was enhanced. Moreover, MMH was scarcely extracted after water treatment for 168 h at 70 °C. As a result, the mechanical properties and flame retardancy of the MMH–O-SEBS–PP composites were well maintained after the water treatment. The modification of the MH endowed the O-SEBS–PP composites with an excellent compatibility and water-resistant performance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47129.     

Influence of Thrower–Stone–Wales defects on the interfacial properties of carbon nanotube/polypropylene composites by a molecular dynamics approach

A molecular dynamics (MD) simulations study is performed on Thrower–Stone–Wales (TSW) defected carbon nanotube (CNT)/polypropylene (PP) composites. We identify the degradation of the CNT and the improvement of the interfacial adhesion between the defected CNTs and PP molecules considering different CNTs with different numbers of TSW defects. By embedding the CNTs into a PP matrix, the effect of the TSW defects on the transversely isotropic elastic stiffness of polymer composites is calculated by MD simulations. Even if the TSW defects degrade the elastic properties of the CNTs, the transverse Young’s modulus and the transverse and longitudinal shear moduli of the composites increase due to the stronger interfacial adhesion between the defected CNTs and matrix, whereas the longitudinal Young’s modulus of the composites decreases. To elucidate the improved interfacial load transfer between the CNTs and the matrix, random polymer chain crystallization onto the surface of CNTs is simulated. The simulation shows that PP chains are wrapped more uniformly onto the surfaces of defected CNTs than onto the pristine CNT. The non-bond adhesion energy between the PP chains and the defected CNTs is greater than that between the PP chains and the pristine CNT.     

Interfacial interactions in calcium carbonate–polypropylene composites. 2: Effect of compounding on the dispersion and the impact properties of surface-modified composites

This study was carried out to investigate the influences of compounding process and surface treatment on calcium carbonate (CaCO₃) filled polypropylene. The compounding process is discussed with reference to a twin-screw extruder and an internal mixer. The calcium carbonate filler was surface-treated with a liquid titanate coupling agent (LICA 12) and stearic acid. Composites of different weight fractions were prepared by both compounding processes, and their impact properties were evaluated. The notched Izod impact strength increased with CaCO₃ content up to a maximum at about 10 vol%, and then decreased. Surface treatment of CaCO₃ filler generally yielded composites of higher impact strength than untreated system. Though LICA 12 was more effective than stearic acid in modifying the filler, the low-cost stearic acid proved to be more effective when dealing with the impact properties of composites. Moreover, the composites from a Brabender Plasti-corder exhibited better gross uniformity than that from the twin-screw extruder. However, good filler dispersion and uniform microscopic morphology, as revealed by SEM microscopy, was observed in the samples from the twin-screw extruder. Polym. Compos. 25:451–460, 2004. © 2004 Society of Plastics Engineers.     

Microstructure and properties of CaO–ZrO2–SiO2 glass–ceramics prepared by sintering

For the development of a new wear resistant and chemically stable glass-ceramic glaze, the CaO–ZrO₂–SiO₂ system was studied. Compositions consisting of CaO, ZrO₂, and SiO₂ were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO₃) and calcium zirconium silicate (Ca₂ZrSi₄O₁₂) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca_1.2Si_4.3Zr_0.2O₈. The CaO–ZrO₂–SiO₂ system showed good properties in wear and chemical resistance because the Ca₂ZrSi₄O₁₂ crystals positively affected physical and mechanical properties.     

Properties of cement–sand-based piezoelectric composites with carbon nanotubes modification

Carbon nanotubes (CNTs) were dispersed in a cement–sand-based piezoelectric composite as conductive fillers to improve its poling efficiency. Specimens were prepared by mixing PZT powders, cement and sand with CNTs. The effect of CNTs ranging from 0 to 0.9 vol% on properties of the composite, including its piezoelectric coefficient, dielectric constant and loss, and sensing characteristic, were characterized. It was found that the addition of CNTs facilitated effective poling under a low electric field of 1 MV/m at room temperature and improved the piezoelectric and dielectric properties of the composite. The composite modified by CNTs achieved optimal properties when the CNTs content was 0.6 vol% and this was verified by the investigation of sensing effects of the composite through compressive tests.     

Quasistatic and dynamic properties of 1–3 composites made by soft molding

The development of the soft mold process allows for the preparation of fine scale 1–3 composites with PZT rods of different size, shape and spacing, which can be used as ultrasonic transducers for frequencies ⩾5 MHz. [Gebhardt, S., Schönecker, A., Steinhausen, R., Hauke, T., Seifert, W. & Beige, H., Fine scale 1-3 composites fabricated by the soft mold process: preparation and modeling. Ferroelectrics, 241 (2000) 67]. By this method, composites with a square, hexagonal and non regular arrangement of PZT rods of different shape have been fabricated and characterized by measuring their quasistatic and dynamic properties. The experimental results were compared with data from finite element method (FEM) modeling and analytical solutions. The vibrational characteristics of the composites were strongly influenced by the rod geometry and the rod arrangement. To evaluate the 1–3 composite performance, modal analysis and modeling of the impedance spectrum were carried out using the FEM package ANSYS.     

Properties of Si3N4–TiN composites fabricated by spark plasma sintering by using a mixture of Si3N4 and Ti powders

Si₃N₄–TiN composites were successfully fabricated via planetary ball milling of 70 mass% Si₃N₄ and 30 mass% Ti powders, followed by spark plasma sintering (SPS) at 1250–1350 °C. The sintering mechanism for SPS was a hybrid of dissolution–reprecipitation and viscous flow. The electrical resistivity decreased with increasing sintering temperature up to a minimum at 1250 °C and then increased with the increasing sintering temperature. The composites prepared by SPS at 1250–1350 °C could be easily machined by electrical discharge machining. Composite prepared by SPS at 1300 °C showed a high hardness (17.78 GPa) and a good machinability.     

Sintering and microstructure of mullite–Mo composites

Mullite–Mo composites of different compositions (0–100 vol.% Mo) were sintered to near theoretical density by pulse electric current sintering (PECS). The densification behaviour and the microstructure of mullite–Mo composites as a function of Mo content were studied. The addition of 10 vol.% Mo significantly enhanced the strength and toughness of monolithic mullite to 556 MPa and 2.9 MPa m^1/2, respectively. SEM observations revealed the modification of discrete isolated Mo particles to continuosly interconnected network with the increase in the Mo content. Mo grains were located at the grain boundaries as well as inside the mullite grains. The addition of Mo to monolithic mullite led to a change in the fracture mode.     

Pressure-less joining of SiCf/SiC composites by Y2O3–Al2O3–SiO2 glass: Microstructure and properties

In this study, Y₂O₃–Al₂O₃–SiO₂ (YAS) glass was prepared from Y₂O₃, Al₂O₃, and SiO₂ micron powders. Thermal expansion coefficient of as-obtained YAS glass was about 3.9 × 10⁻⁶, matching-well with that of SiC_f/SiC composites. SiC_f/SiC composites were then brazed under pressure-less state by YAS glass and effects of brazing temperature on microstructures and properties of resulting joints were investigated. The results showed that glass powder in brazed seam sintered and precipitated yttrium disilicate, cristobalite, and mullite crystals after heat treatment. With the increase in temperature, joint layer gradually densified and got tightly bonded to SiC_f/SiC composite. The optimal brazing parameter was recorded as 1400 °C/30 min and shear strength of the joint was 51.7 MPa. Formation mechanism of glass-ceramic joints was proposed based on combined analysis of microstructure and fracture morphology of joints brazed at different temperatures. Thermal shock resistance testing of joints was also carried out, which depicted decline in shear strength with the increase of thermal shock times. The strength of the joint after three successive thermal shock cycles at 1200 °C was 35.6 MPa, equivalent to 69% of that without thermal shock.