Thermogravimetric characterization of gelcast alumina composites

Gelcasting is a new method for forming advanced ceramics based on obtaining intermediary gels promoted by polimerization “in situ” within the ceramic slurry. Gelcast composites of an ALCOA A-1000 alumina and the copolymer obtained using acrylamide and N,N′-metylene-bisacrylamide as monomers were characterized by thermogravimetry. Polymer distribution was determined by thermogravimetric analysis of small size specimens that were taken from different parts of the alumina composites formed in different shapes. Derivative thermogravimetry was used to identify the resulting polymerization stage within the gelcast body, as well as to study the influence of mold materials and operating conditions. All the composites show an even distribution of the polymer in the bulk, which enables machining in the green state and obtaining high density alumina bodies after sintering.     

Application of synthesized mesoporous titania microspheres for arsenic [(III) and (V)] uptake studies

The present work describes the application of radiotracer technique for studying uptake of arsenic on titanium hydroxide, commercial titanium dioxide (TiO₂) powder (anatase) and synthesized mesoporous titania beads in acidic, neutral, and alkaline conditions. Sol–gel templating method was used to prepare titania–polysaccharide composites, with different polymer contents. Mesoporous titania was obtained by heat treatment of the composite beads in a controlled environment. The synthesis process was optimized, using thermogravimetry analysis. X-ray diffraction patterns confirmed the formation of anatase pure phase titania (TiO₂) at 700 °C in different environments, and scanning electron microscopy studies confirmed uniform pore size distribution. The effect of surface area, polymer content and pH on uptake of arsenic(III) and (V) on the synthesized titania beads was also investigated. Arsenic(V) was found to be retained quantitatively on the titania beads synthesized from 0.8% polymer content titania–polymer composite precursor in neutral to alkaline conditions. Details of the results obtained are discussed.     

Thermal characterization of rubberwood-polymer composites

The thermal properties of five types of radiation-induced wood-polymer composites based on a tropical hardwood, rubberwood (Hevea braziliensis), was studied by oxygen index measurement, differential thermal analysis (DTA) and thermogravimetry (TG). The DTA and TG curves of composites were different from those of rubberwood, which can be attributed to the presence of the incorporated polymers. Of the five composites, the one impregnated with bis(2-chloroethyl)vinyl phosphonate reduced the initial temperature of decomposition, increased the peak temperatures of exothermic reactions, and increased the char yield. Comparison with physical blends of rubberwood and the corresponding polymer provided some evidence of chemical interaction of wood and polymer in some of the composites.     

TG and DSC studies on plaster residues as recycled material

The aim of the present work is to study plaster residues produced in industries in Goiás State (Brazil). The study analyzes the trituration and dehydrating processes of the plaster and compares its chemical, mechanical and physical characteristics to the natural plaster samples aiming its possible recycling. Plaster samples were submitted to X-ray diffraction, infrared spectroscopy, thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. By the comparison of the results obtained for both samples it was observed that they have similar chemical characteristics. No reason was found against the use of recycled plaster.     

Poly(lactic acid) composites with poly(lactic acid)‐modified carbon nanotubes

This work reports the study of the effect of chemical functionalization of carbon nanotubes on their dispersion in poly(lactic acid). The nanotubes were functionalized by the 1,3‐dipolar cycloaddition reaction, generating pyrrolidine groups at the nanotube surface. Further reaction of the pyrrolidine groups with poly(lactic acid) was studied in solution and in the polymer melt. The former involved refluxing the nanotubes in a dimethylformamide/polymer solution; the latter was carried out by direct melt mixing in a microcompounder. The carbon nanotubes collected after each process were characterized by thermogravimetry and by X‐ray photoelectron spectroscopy, showing evidence of polymer bonded to the nanotube surface only when the reaction was carried out in the polymer melt. The composites with polymer modified nanotubes present smaller average agglomerate area and a narrower agglomerate area distribution. In addition, they show improved tensile properties at low CNT concentration and present lower electrical resistivity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3740–3750     

Thermal properties and morphology of high-density polyethylene filled with coffee dregs

Composites of high-density polyethylene (HDPE) and coffee dregs (COFD) were elaborated using four different types (integral, extracted, major size, and minor size) of COFD. The aim was to study the effects of particle size and soluble extraction over the properties of the HDPE. Four blends were made at the proportion of 90–10 % polymer-filler. The materials were evaluated through optical and scanning electron microscopy, differential scanning calorimetry and thermogravimetry/derivative thermogravimetry. The results showed that the integral COFD has a performance similar to the minor size one, and superior to the extracted. The composites degraded in two steps. The first one was in a temperature lower than the neat HDPE, but higher than the processing temperature of the polymer. The melting temperature and the degree of crystallinity of the composites resulted similar to the neat HDPE ones. In general, extraction and particle size of the COFD have little influence on the behavior of the HDPE. The results show that COFD can be used as filler in polymeric composites.     

Heat of hydration as a method for determining the composition of calcined gypsum

The heat of hydration of a fresh, locally produced sample of some industrial gypsum (plaster of Paris, CaSO₄ · 0.5 H₂O) was determined. An adiabatic calorimeter was used for this purpose. The obtained heat of hydration was ?9 cal g^?1, which is higher than that for the hemihydrate (?5 cal g^?1). The calculated heat of hydration for calcium sulphate hemihydrate from the known heats of formation, and using ordinary thermochemical equations, is ?5 cal g^?1. In the same manner, however, the calculated heat of hydration for the anhydrite (CaSO₄) is ?29 cal g^?1. The higher heat of hydration (?9 cal g^?1) for the tested sample than that for the ordinary hemihydrate (?5 cal g^?1) was attributed to the presence of a certain percent of anhydrite. The composition of the tested sample was proposed by applying conventional chemical and rational analyses. The present work suggests the use of the heat of hydration as a tool for determining the composition of calcined gypsum.     

Viscoelasticity and water plasticization of polymer-cellulose composite films and paper sheets

Viscoelastic properties of cellulose microfibril—polymer composites and paper sheets were studied with dynamic mechanical analysis as a function of relative humidity in order to assess the bonding properties in cellulosic networks. The amount of associated water in the composites (equilibrium moisture content) was measured by thermogravimetry. Water plasticization was evidenced by DMA both in composite and paper samples. Polymers with high affinity to water, e.g. carboxymethyl cellulose, clearly increased the water plasticization in the composites. The plasticization behavior of paper sheet samples was also influenced by polymers. However, the effect of polymers on the plasticization was different between the composite and the paper samples. The consideration of fiber bonding domain in paper structure as a gel-like layer consisting of cellulose microfibrils, polymers, and associated water can help to unveil some of the complex mechanisms behind the strength in fibrous cellulosic materials.     

A comparative study on cement hydration and microstructure of cement paste incorporating aminosulfonate–phenol–salicylic acid–formaldehyde and aminosulfonate–phenol–formaldehyde polymer

In this article, the water-soluble aminosulfonate–phenol–salicylic acid–formaldehyde (AH) polymer and aminosulfonate–phenol–formaldehyde polymer (AS) were incorporated into cement paste, and the effect of AH polymer on cement hydration and microstructure of cement paste was compared with AS polymer by means of isothermal calorimetry, X-ray diffraction, thermal analysis, mercury intrusion porosimetry, and scanning electron microscopy. The test results showed that the incorporation of AH and AS polymers into cement paste retards the rate of hydration reaction and reduces the amount of hydration products at early stages of hydration. The use of AH and AS polymers into cement paste also improves pore structure of cement paste. The pore size distribution of cement paste shifts toward smaller pore size scope. A smaller particle size of hydration product can be found in cement paste with AH and AS polymers. The cement paste with AH and AS polymers has a higher pore volume and total porosity. The surface morphologies of cement paste with AH and AS polymers are looser and more homogeneous than blank cement paste. Moreover, at the same dosage of polymer, the effect of AH polymer on the cement hydration and microstructure of cement paste was more significant than that of AS polymer.     

络合滴定法测定半水石膏含量

建立了测定粘胶型石膏绷带含量的方法。采用络合滴定法对半水石膏含量进行测定,考察了供试液制备方法,指示剂等因素。结果表明,络合滴定法能快速有效检测出半水石膏含量,滴定终点清晰,误差小,相对标准偏差RSD为1%,平均回收率为99.8%。所建立的检测方法操作简便,结果准确可靠,重现性好,能有效地控制粘胶型石膏绷带的质量。     

The acquirement of desirable dielectric properties of carbon nanofiber composites based on the controlled crystallization

This study focused on uncovering the relationship among nanofiller, crystallization behavior, and dielectric property of polymer composites. The effects of carbon nanofibers (CNFs) and heat treatment on the crystalline structures and dielectric properties of the semi‐crystalline polymers were analyzed by using high density polyethylene (HDPE) as a matrix, which is a representative of non‐polar polymer and contains only one crystal structure. The experimental results showed that the degree of crystallinity, size distribution of crystallity, and relative amount of different crystal planes in the HDPE matrix were changing due to the addition of CNFs. With the increase of CNF loading, the dielectric constant, dielectric loss and AC conductivity of the HDPE composites were increased, presenting a typical percolation characteristic, and the dependence of the dielectric constant on frequency became more obvious. All kinds of electronic transmission, polarization effect, and relaxation behaviors in CNF/HDPE composite system were deeply analyzed. After heat treatment, the degree of crystallinity of HDPE composites was decreased with the enhanced cooling rate. For the CNF/HDPE composites with nanofiller content slightly higher than the percolation threshold, the significant increase of the dielectric constant and the dramatical reduction of the dielectric loss over a wide frequency range were realized simultaneously through rapid cooling treatment. The research indicated that a general commercial polymer material with excellent dielectric properties, which exhibited a high dielectric constant and a low dielectric loss, can be obtained by a simple technical approach different from traditional fabrication method of threshold composites.     

利用聚合物乳液合成聚甲基丙烯酸甲酯/二氧化硅纳米杂化材料

通过正硅酸乙酯分别在聚甲基丙烯酸甲酯乳液和四氢呋喃溶液中的溶胶－凝胶反应制备出不同的聚甲基丙烯酸甲酯／二氧化硅复合材料。利用扫描电镜、透镜电镜、差热分析和热失重对试样进行了分析。结果表明，利用聚合物乳液可以获得纳米分散的聚甲基丙烯酸甲酯／二氧化硅复合材料，并且在某种程度上其分散尺度小于利用聚合物溶液获得的复合材料。同时，利用聚合物乳液来制备聚甲基丙烯酸甲酯／二氧化硅杂化材料更有利于凝胶过程中二氧化硅网络的形成。     

Thermal Analysis of Some Environmentally Degradable Polymers

The thermal characteristics of a series of degradable polymers have been investigated using thermogravimetry and differential scanning calorimetry. While the results of the thermogravimetry experiments suggest that the thermal stability of the polymers should not pose any problems at the temperatures that can be expected in a commercial composting process (60°C), phase changes associated with some of the polymers investigated may cause problems in the interpretation of data from composting degradation studies. Several biodegradable polymers were observed to have melt transitions at temperatures similar to those found in a composting environment. Consequently, under the controlled composting conditions used to evaluate biodegradable polymers, degradation of a polymer may be inferred, while actually the polymer has merely undergone a phase change. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure and dielectric properties of a thermoplastic blend containing dispersed metal

In the present work broadband dielectric relaxation spectroscopy measurements were employed to investigate the dielectric properties of polymer composites. A polyethylene/polyoxymethylene (PE/POM) thermoplastic blend was used as a matrix, while the inclusions were iron (Fe) particles. For comparison, the two pure polymers- PE and POM- were used as a matrix, too. In the PE/POM-Fe composites, the polymer matrix is two-phase and the filler particles are localized only in the POM phase, resulting in an ordered distribution of the dispersed filler particles within the blend. In PE-Fe and POM-Fe composites, the filler spatial distribution is random. The behaviour of all the composites studied is described in terms of the percolation theory. The PE/POM-Fe composites, based on the PE/POM blend, demonstrate different electrical behaviour compared to that of POM-Fe and PE-Fe systems. The percolation threshold value of the PE/POM-Fe composites was found much lower than that of the other two systems. The results were related to the microstructure of the composites. A schematic model for the morphology of the composites studied has been proposed. This model explains the peculiar behaviour of the PE/POM-Fe composites by taking into account the ordered distribution of the filler particles in a binary polymer matrix. Optical microscopy photographs confirm this model.     

Thermal stability of surface-esterified cellulose and its composite with polyolefinic matrix

Thermal stability of hydrophobized cellulose powders was investigated from the perspective of potential use as filler in non-polar polyolefinic matrix. The hydrophobization was done by heterogeneous esterification with three carboxylic acids which differ in chain length (3, 10 and 18 carbons). Data measured by means of thermogravimetry (TG) were recalculated according to model-free isoconversional method to construct time–temperature plots. It was demonstrated that the esterification significantly decreases thermal stability of the material, which reduces feasible processing window. Under non-oxidative atmosphere, the single-step decomposition of materials is prevailing, while the process is more complex in air. In both cases the oleic acid esters showed the lowest stability and the original cellulose was the most stable. Finally, all powders were compounded with polyethylene or polypropylene. Obtained composites were then subjected to color measurement and TG. Even though the materials were partly degraded, which was indicated by the yellowish hue of the composites, virtually no impact of the filler pyrolysis on the polymer matrix decomposition was observed, particularly in case of decanoyl esters.     

High-impact polystyrene/polyaniline membranes for acid solution treatment by electrodialysis: preparation, evaluation, and chemical calculation

In this study different membranes were produced, aiming to evaluate their use in electrodialysis. These membranes were produced using conventional polymer (high-impact polystyrene) and polyaniline. The membrane characterization was done by FTIR spectroscopy, scanning electron microscopy (SEM), and thermogravimetry (TGA). The studies of the zinc and proton extraction ionic transport through the membranes were evaluated using a three-compartment cell. The results obtained using the produced membranes were compared to the results obtained with the commercial membrane Nafion 450. It was found that a synthesized membrane can be used to recover zinc in acid media. In addition, a preliminary computational essay about the structures of PAni and CSA is presented.     

Thermal behavior of cardanol resin reinforced 20 mm long untreated bagasse fiber composites

Recently the attention in composite materials reinforced with natural fibers has significantly increased due to the new environmental legislation as well as consumer pressure that forced manufacturing industries to search substitutes for the conventional materials, e.g., glass fibers. In this way, the objective of the paper was to evaluate the thermal properties of sugarcane bagasse fiber-cardanol resin composites. Fibers were cut down to 20?mm length in diagonally. These fibers were mixed with the cardanol and epoxy resin, and fabricate in a biocomposites with different compositions, such as 0, 5, 10, 15, and 20?wt%. The thermal properties were evaluated by thermal gravimetric analysis and differential thermogravimetry analysis and also chemical formulation studied in Fourier transform infrared spectroscopy. The results showed the improved thermal strength of the composites in comparison to the neat polymer (0?wt%).     

超浓乳液聚合制备PU/PS的SIPN粉状树脂研究

将聚氨酯予聚体 (PU ) 苯乙烯 (St)的复合体系 ,用超浓乳液聚合方法制备了半互穿聚合物网络(SIPN)复合聚合物 ,得到了用聚氨酯予聚体改性的聚苯乙烯 (PU/PS)SIPN粉状树脂 .研究了分散相的比例(α)和聚合温度对聚合稳定性及聚合转化率 -时间的关系 ;测定了聚合物胶乳粒子的大小、形态 ,玻璃化温度 ,动态力学性能等 .结果表明 ,超浓乳液聚合较之本体聚合具有较高的聚合速率 ,容易控制所制备的胶乳粒径 ,能够制得PU/PS复合聚合物的SIPN粉状树脂 .该粉状树脂便于加工 ,具有良好的强韧性 ,有利于扩大应用     

Thermal stability and glass transition behavior of PANI/MWNT composites

Polyaniline/multi-walled carbon nanotube (PANI/MWNT) composites were prepared by in situ polymerization. Transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were used to characterize the PANI/MWNT composites. Thermal stability and glass transition temperature (T _g) were measured by thermogravimetry (TG) and temperature modulated differential scanning calorimetry (TMDSC), respectively. The TG and derivative thermogravimetry (DTG) curves indicated that with augment of MWNTs content, the thermal stability of PANI/MWNT composites increased continuously. While, T _g increased and then decreased with the MWNTs content increasing from 0 to 20 mass%.     

Plasters in the Cellars of the Visconti Castle in Pavia. Physico-chemical characterization

An archaeometric investigation on plaster samples taken from the cellars of the Visconti Castle in Pavia has brought out the existence of several layers and colour films of various periods. The oldest plaster spread over the masonry is formed with three main layers. Above them, one film of bluish-black colour can be found on the arcs and on the bearing walls. On this black layer, a white film of calcitic composition, containing also apatite fragments, was spread. These ancient materials were subsequently covered in more recent times with plasters having different compositions and textures. In the present paper the properties of the three main plaster layers and those of the black film are reported in detail. The thermal behaviour of these materials was studied by means of differential thermal analysis and thermogravimetric analysis. The study was completed with scanning electron microscopy,microprobe analysis and X-ray diffraction on powders. The results obtained provide interesting clues for advancing reasonable hypotheses both on the methods adopted in ancient building yards, and on the techniques for the production of the pigments employed. This revised version was published online in July 2006 with corrections to the Cover Date.