Free‐volume effects on the thermomechanical performance of epoxy–SiO2 nanocomposites

In this study, free‐volume effects on the thermal and mechanical properties of epoxy–SiO₂ nanocomposites were investigated. SiO₂ particles ranging from 15 nm to 2 µm were used, and the nature of the matrix–filler interphase was modified by surface grafting. Nanoparticles 15 nm in diameter yielded an increase in the glass‐transition temperature (T_g) of the composites up to 5 °C; at the same time, they increased the storage modulus (E′) from 2340 to 2725 MPa. Conversely, large particles markedly decreased both T_g and E′; this suggested the pivotal role of nanoparticle size on the final properties of the nanocomposite. The functionalization of SiO₂ nanoparticles markedly improved their dispersion within the epoxy matrix. The positron annihilation lifetime spectroscopy results indicate that the free volume strongly depended on the interphase. These experimental findings obtained here could be extrapolated to industrially relevant nanocomposites and could provide a rationale for the comprehension of free‐volume effects on the thermal and mechanical properties of nanocomposite materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45216.     

Characterizations of UV‐curable montmorillonite/epoxy nanocomposites prepared by a hybrid of chemical dispersion and planetary mechanical milling process

Ammonium salt, [2‐(methacyloyloxy)ethyl] trimethylammonium methyl sulfate (MAOTMA), was adopted to modify montmorillonite (MMT) via the cationic exchange process in an acidic environment and a successful enlargement of MMT lamellar spacing from 1.18 to 1.39 nm was identified by x‐ray diffraction and Fourier‐transform infrared spectroscopy. Accordingly, UV‐curable epoxy nanocomposite resins containing various amounts of MAOTMA‐modified MMT were prepared with the aid of a planetary mechanical milling process. Transmission electron microscopy revealed a uniform dispersion of exfoliated MMT lamella in epoxy matrix, leading to the distinct improvements on thermal stability and thermal expansion property of nanocomposite samples. Calcium (Ca) test indicated that the good dispersion of MMT fillers in polymer effectively suppresses the moisture permeation in sample matrix. More than twofold increment on retention time of 5% Ca hydrolysis and 20% improvement on the permeation kinetic parameters were observed in the nanocomposite sample containing 8 wt % MMT in comparison with the pristine epoxy sample. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Specific features of the relaxation processes in As2Se3 films prepared by different methods

The specific features of the processes of charge transfer and accumulation in thin films of arsenic triselenide As₂Se₃ are investigated by measuring the isothermal relaxation of dark electric currents. It is established that the relaxation properties of the films substantially depend on the method used for their preparation, which, apparently, can be associated with the structural features of this class of materials. Moreover, it is confirmed that the relaxation of the electric current in the films of chalcogenide glasses under investigation occurs through a non-Debye mechanism, irrespective of the preparation technique.     

Characteristics of polyvinylpyrrolidone-layered silicate nanocomposites prepared by attrition ball milling

Polyvinylpyrrolidone (PVP)/sodium montmorillonite (MMT) nanocomposites prepared via the solution intercalation method were investigated by UV/vis, SEM, X-ray diffraction, TEM, FT-IR and PLM (polarized light microscopy). PVP/MMT nanocomposites show exfoliation below 20 wt% MMT and intercalation above this concentration. Nanocomposites retain good optical clarity and increased thermal resistance with MMT content. The compatibility between PVP and MMT and their enhanced properties may be explained by hydrogen bonding interactions. In addition, the nanocomposites prepared under more rigorous mixing conditions show better transparency because the smaller particle sizes are induced. In addition, the study on optically clear PVP/MMT suspensions helps one to understand how optical anisotropy of MMT is affected by the existence of polymer in aqueous solution.     

Study of morphological and mechanical performance of amine‐cured glassy epoxy–clay nanocomposites

The effect of three different alkylammonium‐modified montmorillonite on morphological and mechanical properties of glassy epoxy‐amine nanocomposites is reported. Small amounts of clays <10 phr (part per hundred of resin) were used in each system of nanocomposite. The morphology of the prepared nanocomposites was performed by means of X‐ray diffraction and transmission electron microscopy. Differential scanning calorimetry (DSC) was used to investigate the glass transition temperatures (T_g). Mechanical properties were based on tensile characteristics (Young's modulus), impact strength, and fracture toughness. The measured moduli were compared to theoretical predictions. Scanning electron microscopy was used to study the morphological structure of the fracture surfaces of impacted specimens. It was found that at a low content of 2 phr (1.2 wt %) of nanoclays, the impact strength and the fracture toughness were improved by 77 and 90% respectively, comparatively to the neat epoxy, whereas DSC revealed a reduction of the T_g of nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Film formation from PS/AL2O3 nanocomposites prepared by dip‐drawing method

In this study, steady state fluorescence (SSF) and UV–vis (UVV) techniques were used to examine film formation from pyrene (P) labeled polystyrene (PS) latex/Al₂O₃ (PS/Al₂O₃) composites prepared by the dip‐drawing method. The effects of dip‐drawing rates and dipping time in Al₂O₃ sol on film formation behavior and the morphology of PS/Al₂O₃ films were investigated. Films were prepared first by casting PS dispersion on clean glass substrates which creates a close‐packed array of PS sphere (203 nm) templates. These templates were then covered with Al₂O₃ utilizing the dip‐drawing method for various dip‐drawing rates and dipping times in Al₂O₃ sol. The film formation of these composites was studied by annealing them at a temperature range of 100°C to 270°C and monitoring the scattered light (I_sc), fluorescence (I_P), and transmitted light (I_tr) intensities after each annealing step. The structural properties of the composite films were analyzed with a scanning electron microscope (SEM). The results demonstrated that the film formation behavior and morphology of composites depended mainly on dipping time, and no dependence on the dip‐drawing rate was observed. The optical results indicated that PS/Al₂O₃ films undergo complete film formation independent of the dip‐drawing rate and dipping time. Additionally, the film formation stages were modeled and the corresponding activation energies were determined. After completion of film formation, PS polymers were extracted to obtain porous Al₂O₃ thin films. Highly ordered porous structures were observed for long dipping time in Al₂O₃ sol but no change was observed for different dip‐drawing rates, confirming the optical data. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Electrical and mechanical properties of acrylonitrile‐butadiene‐styrene/multiwall carbon nanotube nanocomposites prepared by melt‐blending

The electrical properties in polymer/carbon nanotube (CNT) nanocomposites are governed not only by the degree of dispersion but also to a greater extent on the aspect ratio of the CNTs in the final composites. Melt‐mixing of polymer and CNTs at high shear rate usually breaks the CNTS that lowers the aspect ratio of the nanotubes. Thus, homogeneous dispersion of CNTs while retaining the aspect ratio is a major challenge in melt‐mixing. Here, we demonstrate a novel method that involves melt‐blending of acrylonitrile‐butadiene‐styrene (ABS) and in situ polymerized polystyrene (PS)/multiwalled CNT (MWCNT) nanocomposites, to prepare electrically conducting ABS/MWCNT nanocomposites with very low CNT loading than reported. The rationale behind choosing PS/MWCNT as blending component was that ABS is reported to form miscible blend with the PS. Thus, (80/20 w/w) ABS/(PS/MWCNT) nanocomposites obtained by melt‐blending showed electrical conductivity value ≈1.27 × 10^?6 S cm^?1 at MWCNT loading close to 0.64 wt %, which is quite lower than previously reported value for ABS/MWCNT system prepared via solution blending. Scanning electron microscopy and differential scanning calorimetry analysis indicated the formation of homogenous and miscible blend of ABS and PS. The high temperature (100°C) storage modulus of ABS (1298 MPa) in the nanocomposites was increased to 1696 MPa in presence of 0.64 wt % of the MWCNT. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The influence of Sb on glass‐forming ability of Ga‐containing As2Se3 glasses

Effect of As to Sb substitution on glass‐forming ability of As₂Se₃ glass under Ga additions was comprehensively studied using optical spectroscopy in visible and IR regions, differential scanning calorimetry, X‐ray diffraction as well as Raman scattering techniques. The crystallization processes enhanced by Ga additions to As₂Se₃ glass were significantly suppressed under such As to Sb substitution. Following conventional synthesis, it was possible to substitute up to 50% of As by Sb within Ga_y(As_0.40?xSb_xSe_0.60)_100?y cut‐section without essential impact on glassy state, thus improving optical properties in the IR region by lowering the phonon energy. In the case of Ga_y(As_0.28Sb_0.12Se_0.60)_100?y cut‐section, up to 8 at.% of Ga can be introduced without crystallization, whereas in case of Ga_y(As_0.40Se_0.60)_100?y system, glass‐forming ability is limited just up to 3 at.% of Ga. The prepared Ga₅(As_0.28Sb_0.12Se_0.60)₉₅ glass composition was shown to be the richest in Ga keeping its vitreous state, good optical and thermodynamic properties allowing further rare‐earth doping and fiber drawing.     

Free‐volume hole properties of two kinds thermoplastic nanocomposites based on polymer blends probed by positron annihilation lifetime spectroscopy

Two type of nanocomposites—an immiscible blend, high density polyethylene/polyamide 6 (HDPE/PA‐6) with organomodified clay, and a compatibilized blend, high density polyethylene grafted with acrylic acid/PA‐6 (PEAA/PA‐6) with organomodified clay—were prepared via melt compounding. X‐ray diffraction and transmission electron microscopy results revealed that the clay was intercalated and partially exfoliated. Positron annihilation lifetime spectroscopy has been utilized to investigate the free‐volume hole properties of two type of nanocomposites. The results show a negative deviation of free‐volume size in PEAA/PA‐6 blend, and a positive deviation in HDPE/PA‐6 blend, and I₃ has a greater negative deviation in compatibilized blend than in immiscible blend due to interaction between dissimilar chains. For nanocomposites based on polymer blends, in immiscible HDPE/PA‐6/organomodified clay system, the variation of free‐volume size with clay content is not obvious and the free‐volume concentration and fraction decreased. While in the case of compatibilized PEAA/PA‐6/organomodified clay nanocomposites, complicated variation of free‐volume properties due to interactions between two phases and organomodified clay was observed. And the interaction parameter β shows the interactions between polymers and organomodified clay. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2463–2469, 2006     

Improvement of wetability,sinterability, mechanical and electrical properties of Al2O3-Ni nanocomposites prepared by mechanical alloying

The wetability improvement and particle size reduction of alumina/Ni composites through mechanical alloying were addressed. Their effect on the sinterability (at high temperature), mechanical and electrical properties were studied. Al₂O₃ matrix nanocomposites reinforced with different volume fractions of Ni up to 10 vol% were prepared by mechanical alloying. The milled powders were cold pressed and sintered at different firing temperatures up to 1600 °C. The morphology of powders and the microstructure of sintered bodies were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), respectively. Furthermore, relative density, apparent porosity, mechanical properties and electrical resistivity of the sintered composites were investigated. The results revealed that Al₂O₃ matrix was successfully coated with Ni thin film through mechanical alloying; the thickness of coat was increased with increasing the Ni content. Moreover, the increasing of both Ni content and sintering temperature up 1600 °C, led to a remarkable increase in the relative density and facture toughness of the sintered specimen. On the other hand, microhardness and elastic modulus were decreased with increasing of Ni content, while they increased significantly with the increase of sintering temperature. The electrical resistivity was decreased with increasing Ni content and sintering temperature.     

Morphology and mechanical properties of polypropylene/polyamide 6 nanocomposites prepared by a two‐step melt‐compounding process

Polypropylene/polyamide 6 blends and their nanocomposites with layered silicates or talc were prepared in a melt‐compounding process to explore their mechanical performance. The thermomechanical behavior, crystallization effects, rheology, and morphology of these materials were studied with a wide range of experimental techniques. In all cases, the inorganic filler was enriched in the polyamide phase and resulted in a phase coarsening of the polypropylene/polyamide nanocomposite in comparison with the nonfilled polypropylene/polyamide blend. The mechanical properties of these nanoblends were consequently only slightly better than those of the pure polymers with respect to the modulus, whereas the impact level was below that of the pure polymers, reflecting the heterogeneity of the nanoblend. Polymer‐specific organic modification of the nanoclays did not result in a better phase distribution, which would be required for better overall performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 283–291, 2006     

Polarization properties of modified As2Se3 films

The influence of modifying Bi and Pb impurities on the polarization properties of As₂Se₃ thin films is investigated. It is found that the relaxation and contact parameters of the samples under study change as the modifier content increases.     

Improved mechanical properties and structure of PP/nano‐CaCO3 blends prepared by low‐frequency vibration injection molding

BACKGROUD: Melt vibration technology was used to prepare injection samples of polypropylene (PP)/nano‐CaCO₃ blends. It is well known that nano‐CaCO₃ particles are easy to agglomerate owing to their large surface energy. Improving the distribution of nano‐CaCO₃ particles in PP/nano‐CaCO₃ blends is very important for enhancing the mechanical properties. In this work, low‐frequency vibration was imposed on the process of injection molding of PP/nano‐CaCO₃ blends. The aim of importing a vibration field was to change the crystal structure of PP as we studied previously and improve the distribution of nano‐CaCO₃ particles. Furthermore, the mechanical properties were improved. RESULTS: Through melt vibration, the mechanical properties of PP/nano‐CaCO₃ samples were improved significantly. Compared with conventional injection molding, the enhancement of the tensile strength and impact strength of the samples molded by vibration injection molding was 17.68 and 175.96%, respectively. According to scanning electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry measurements, it was found that a much better dispersion of nano‐CaCO₃ in samples was achieved by vibration injection molding. Moreover, the crystal structure of PP in PP/CaCO₃ vibration samples changed. The γ crystal form was achieved at the shear layer of vibration samples. Moreover, the degree of crystallinity of PP in vibration samples increased 6% compared with conventional samples. CONCLUSION: Concerning the microstructure, melt vibration could effectively change the crystal structure and increase the degree of crystallinity of PP besides improving the distribution of nano‐CaCO₃ particles. Concerning the macrostructure, melt vibration could enhance the mechanical properties. The improvement of mechanical properties of PP/nano‐CaCO₃ blends prepared by low‐frequency vibration injection molding should be attributed to the even distribution of nano‐CaCO₃ particles and the formation of γ‐PP and the increase of the degree of cystallinity. Copyright © 2007 Society of Chemical Industry     

Free‐volume microprobe study of iodine diffusion in polymers

The effect of iodine sorption on the free‐volume of three polymers, namely, acrylonitrile–butadiene–styrene, poly(ethylene terephthalate) and polycarbonate have been investigated by the positron annihilation lifetime technique. Diffusion coefficients have been evaluated from the sorption curves using Crank's solution for Fick's second law of diffusion. The positron results are explained in terms of iodine filling the free‐volume holes, swelling and conformational changes. It has also been found that the diffusion process in acrylonitrile–butadiene–styrene and poly(ethylene terephthalate) deviates from Fick's law of diffusion whereas in polycarbonate, the diffusion process obeys Fick's law. Further, for polymers in which diffusion deviates from Fick's law, the sorption process has been separated into diffusion‐controlled (Fickian) and relaxation‐controlled (non‐Fickian) parts using the dual‐mode sorption model. Interestingly, the present results show that the polymers which deviate from Fickian diffusion also deviate from Fujita's free‐volume theory of diffusion and vice versa. The positron results also indicate that sorbed iodine in the polymer acts as an inhibitor of ortho‐positronium. © 2001 Society of Chemical Industry     

Thermal,mechanical, and barrier properties of polyethylene terephthalate‐platelet nanocomposites prepared by in situ polymerization

This study used in situ polymerization to prepare polyethylene terephthalate (PET) nanocomposites incorporating Ethoquad‐modified montmorillonite (eMMT), unmodified hectorite (HCT), or phenyl hectorite (phHCT) particles to study the impact of platelet surface chemistry and loading on thermal, mechanical, and gas barrier properties. eMMT platelets reduced the PET crystallization rate without altering the ultimate degree of crystallinity. In contrast, HCT and phHCT platelets accelerated the polymer's crystallization rate and increased its crystallinity. DMA results for thermally‐quenched samples showed that as T increased past glass transition temperature (T_g), HCT and phHCT nanocomposites (and control PET) manifested precipitous drops in G′ followed by increasing G′ due to cold crystallization; in contrast, eMMT nanocomposites had much higher G′ values around T_g. This provides direct evidence of eMMT reinforcement in thermally‐quenched eMMT nanocomposites. These results suggest that eMMT has a strong, favorable interaction with PET, possibly through Ethoquad‐PET entanglement. HCT and phHCT have a fundamentally different interaction with PET that increases crystallization rate and T_g by 11 to 17°C. Water barrier improvement in eMMT nanocomposites agrees with previously published oxygen barrier results and can be rationalized in terms of a tortuous path gas barrier model. POLYM. ENG. SCI., 52:1888–1902, 2012. © 2012 Society of Plastics Engineers     

粉体热压法制备As2Se3硫系玻璃研究

本研究尝试将As₂Se₃红外硫系透镜生产过程中产生的块体玻璃废料进行回收利用,首先将清洗后的块体玻璃废料球磨成粉体,然后采用粉体热压技术实现高光学质量As₂Se₃玻璃片的制备。研究了粉体粒度、热压参数对制备的As₂Se₃玻璃光学性能的影响,对比了粉体热压法和熔融淬冷法制备的As₂Se₃玻璃的性能,评估了通过粉体热压途径制备红外硫系玻璃的可行性。结果表明:随着球磨时间的延长,As₂Se₃玻璃粉体的平均颗粒尺寸逐渐减小,且颗粒尺寸的分布趋于更加均匀;使用平均颗粒尺寸为9.7 μm的粉体(球磨10 min),在压力为40 MPa、热压温度为250 ℃、热压时间为10 min的条件下获得的热压玻璃的致密度达到99.8%,其折射率与熔融淬冷法制备的玻璃的折射率接近(在10 μm波长的折射率差仅为0.003),在10 μm波长的透过率达61%(理论透过率为63.7%)。通过进一步提高玻璃粉体的纯度和尺寸均匀性,有望制备出与熔融淬冷法制备的玻璃性能相当的热压玻璃。     

Structure property relations of copolymerised polypropylene /SiO2 nanocomposites prepared by solid state shear milling (S3M) method

Abstract

In the present paper, solid state shear milling (S³M) method was used to prepare the copolymerised polypropylene (Co-PP)/nano-SiO₂ composites under the conditions of solvent free and non-organic treatment. The change of phase morphology and arrangement of SiO₂ under mechanical force were firstly observed in the complex multiphase and multicomponent Co-PP/nano-SiO₂ composite. The effect of milling cycles on the phase structure and mechanical properties was studied. It was found that the S³M method was an effective way which can adjust the phase structure of composite through change of milling cycles. After 20 milling cycles, the composite can form a structure with a lot of SiO₂ particles around the ethylene–propylene copolymer phase, the Charpy notched impact strength of the composite with 4 wt-%SiO₂ particles can be largely improved from 24·2 to 38·2 kJ m^–2. While after 30 milling cycles, the composite can form a structure with SiO₂ particles dispersed more uniformly in the Co-PP matrix. However, with this structure, the prepared composite has higher stiffness but the notched impact strength could not be greatly improved. The mechanism of the toughening effect is discussed and the structure property relation established.     

Conducting polyaniline‐titanium dioxide nanocomposites prepared by inverted emulsion polymerization

Conducting polyaniline (PAni)‐titanium dioxide (TiO₂) nanocomposites have been synthesized by the inverted emulsion polymerization method. Aqueous mixtures of aniline, a free‐radical oxidant, and/or TiO₂ nanoparticles (∼25 nm in diameter; mixture of anatase and rutile) are utilized to synthesize the hybrid nanocomposites. The polymerization is carried out in an organic solvent (chloroform, CHCl₃) in the presence of a protonic acid (hydrochloric acid, HCl) as a dopant and an emulsifier (cetyl trimethylammonium bromide). The resultant PAni‐TiO₂ nanocomposites are characterized with their structural, morphological, conducting, and optical properties. SEM and TEM images represent the PAni‐TiO₂ nanocomposites with the diameter range of 50–200 nm. Electrical conductivities are checked by standard four‐point probes method and found to be 0.38 S/cm for bulk PAni and 0.11 S/cm for PAni‐TiO₂ nanocomposites. UV–visible absorption shows two electronic bands at about 320 and 596 nm for bulk PAni and the blue‐shifted bands with the intensity changes due to the formation of PAni‐TiO₂ composites. Thermogravimetric analysis reveals that the composites have a higher degradation temperature than the PAni alone. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

PVDF/BaTiO3/carbon nanotubes ternary nanocomposites prepared by ball milling: Piezo and dielectric responses

Nanocomposites based on poly(vinylidene fluoride) (PVDF) filled with barium titanate, BaTiO₃, (BT) particles, and multiwalled carbon nanotubes (MWCNTs) were prepared by high-energy ball milling (HEBM) and subsequent hot pressing. This method of materials preparation allowed obtaining uniform dispersions of the nanofillers. The influence of the particles on the polymer structure and morphology was studied. To understand the origin of changes in the PVDF properties, thermal and electrical behaviors of the PVDF/BT/MWCNT nanocomposites were studied as a function of composition. The addition of BT, MWCNT, or its mixture had not any influence on the PVDF polymorphism. However, calorimetric results pointed out that the presence of the nanofillers exerted nucleation mainly ascribed to the surface to volume ratio of the nanoparticles. The capacitance of the composites increased as the nanofiller content increased, being the effect mainly dependent on the surface to volume ratio of the nanoparticles. The dielectric behavior of the materials as a function of frequency was modeled by a Debye equivalent circuit only below the percolation threshold respect to the amount of MWCNT. The piezoelectric behavior of the ternary nanocomposites was highly affected by the incorporation of the nanofillers only when high dielectric losses occurred above the percolation threshold. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47788.     

固相剪切碾磨制备高填充聚丙烯木塑复合材料的形貌结构与力学性能

利用磨盘形力化学反应器优异的粉碎、分散、混合和力化学反应的多重功能以及增容剂PP-g-MAH的良好增容作用制备了综合性能优良的聚丙烯(PP)/木粉(WF, 80%,质量分数)高填充木塑复合材料,研究了磨盘碾磨、增容剂以及复合方式对PP/WF木塑复合体系的粒径分布、力学性能和形貌结构等的影响.结果表明,不同碾磨次数的PP/WF复合粉体的粒径呈双峰分布,适当增加碾磨次数有利于PP粒径的降低及木粉的均匀分散.随碾磨次数的增加,PP/WF复合材料的拉伸和弯曲性能先增加后下降,但缺口冲击强度一直呈小幅下降趋势.PP-g-MAH的引入及其含量增加均有利于PP/WF复合材料力学性能的大幅改善,其中弯曲模量在增容剂含量为5%(质量分数)时最佳.此外,磨盘碾磨制备的PP/WF复合材料的力学性能优于常规密炼复合法.上述力学性能变化归因于磨盘碾磨改善了PP/WF高填充复合体系中木粉的分散性以及加入的PP-g-MAH显著改善了体系的相容性,其中PP-g-MAH的增容机理为磨盘碾磨剪切力场作用下PP-g-MAH与木粉表面羟基发生了力化学酯化接枝反应.