Improvement of thermal and mechanical properties of a phenolic resin nanocomposite by in situ formation of silsesquioxanes from a molecular precursor

Silsesquioxanes are formed in situ during mixing and curing of a phenolic resin and a molecular silane precursor (3‐(triethoxysilyl)‐1‐propaneamine) yielding a nanocomposite. As indicated by a higher onset temperature, a higher characteristic decomposition temperature, and a lower maximum heat flow, the thermal stability of the nanocomposite is significantly improved over the pristine resin. Moreover, the bending strength and the strain at break could also be enhanced by 36% and 51%, respectively. The nanocomposite was characterized by ²⁹Si solid‐state NMR, STEM/EDS, TGA, DSC, and three point bending tests. The STEM/EDS measurements showed a homogenous distribution of silsesquioxanes in the phenolic resin. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterisation of luminous polypropylene/phosphor strontium aluminate nanocomposite fibres with enhanced dyeability

Phosphor strontium aluminate (SrAl₂O₄: Eu²⁺, Dy³⁺) nanoparticles, SAOED, were melt compounded with polypropylene on an internal mixer to prepare a uniform mixture with polymer and the resulting materials were granulated. PP/SAOED nanocomposite fibres were then produced by melt spinning method at the take-up speed of 1000?m?min^?1. Morphological, thermal, structural and luminescent properties of the luminous fibres were studied by SEM, differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and fluorescence spectrophotometer. The luminous fibres were then knitted and dyed to investigate the effects of SAOED nanoparticles on the dyeability of fibres. SEM results showed that with increasing SAOED nanoparticle amounts, the agglomerates of SAOED nanoparticles were appeared on the fibre surface. DSC results indicated that the SAOED nanoparticles did not affect melting and crystallisation behaviours significantly. WAXD patterns revealed that the crystal type of luminous nanocomposite fibres did not change and was still the α-monoclinic crystal form. The luminous nanocomposite fibres were found to have inferior tensile properties as compared to the neat PP fibre. From fluorescence spectrophotometer results, it can be seen that fibres excited at the wavelength of 400?nm, showed an emission peak at 550?nm and had green light. With increasing the amount of SAOED nanoparticles in the fibres, emission peak intensity of luminous fibres increased and also the fabric dyeability was improved.     

Catalytic initiation of polyacrylonitrile stabilization

A catalytic surface treatment of polyacrylonitrile fibres by dibutyltin dimethoxide is investigated as to its capacity to facilitate the stabilization of the fibres to produce a satisfactory carbon fibre precursor. The stabilization is based on a combination of the catalytic treatment step and of the usual thermal oxidation step which follows. The effectiveness of the surface treatment is determined through comparing physical, thermal and mechanical properties of stabilized fibres with and without catalytic pre-treatment. The results show that a 1 minute catalytic treatment shortens the usual 220°C thermal oxidation process by at least 2 hours, and that the process is applicable in particular to polyacrylonitrile fibres which are ‘slow oxidizers’ in general due to their chemical composition.     

Effect of Montmorillonite Clay Nanoparticles on the Properties of Polypropylene Fibres

Polypropylene and nanocomposite polypropylene fibres were successfully prepared via a melt spinning process. The prepared fibres were characterized by TGA and SEM. The results obtained show that the addition of MMT clay in the fibre induces a higher thermal stability. Water absorption and mechanical properties of the fibres were improved by the introduction of MMT clay nanoparticles in the fibre. Dyeing studies underlined the effect of the clay on the dyeability of the fibres which improved the accessibility of the fibre for both acid and disperse dyes. Moreover, it was observed, that polypropylene and nanocomposites polypropylene fibres were satisfactorily dyed with disperse dyes more than with acid dyes.     

Fibres for use at highest temperatures

Materials having gained importance over the past decade are – in addition to the developments of high temperature-resistant polymer fibres – various types of fibrous materials, being distinguished by their resistance to temperatures exceeding 1000°C. These materials are in general inorganic compounds formed into fibres by special shaping methods. The distinguished properties of some of these fibre types are high mechanical strength, oxidation resistance, electrical conductivity and light weight, apart from their temperature resistance. The main processes used for their manufacture are: drawing of very fine filaments, vapour deposition of compounds in the form of fibres, and spinning of inorganic filaments by the viscose process. This paper discussed metal fibres and fine filaments as well as oxide, carbide and nitride filaments of the third and fourth group of the periodic system of elements, as far as they are of importance. Also discussed will be fibres of boron, silicon carbide, silicon nitride and boron carbide being representative of the vapour deposition process and also fibres of aluminium oxide, titanium oxide, silicon dioxide being representative of the viscose process, as well as other types. Only a small amount of fibres are being produced by the mentioned processes. Carbon fibres are made in general by full thermal decomposition of infusible, organic fibres in inert atmosphere. Their manufacture will be detailed together with their properties and various fields of application. Concepts of the chemistry of thermal decomposition will be illustrated and also the connections between the structure of the basic materials and those of carbon filaments.     

PbSnO_3@rGO纳米复合物的制备及其对CL-20热分解的影响

采用水热法制备了还原氧化石墨烯(rGO)负载PbSnO_3的纳米复合物(PbSnO_3@rGO),并通过XRD、SEM等方法对其进行了表征;用DSC法分析了制得的PbSnO_3@rGO和PbSnO_3-TDI还原型催化剂(r-PbSnO_3-TDI)对六硝基六氮杂异伍兹烷(CL-20)热分解的催化效果。结果表明,rGO作为基底负载PbSnO_3可以有效解决PbSnO_3纳米颗粒的团聚问题,极大地提高了其分散性;PbSnO_3@rGO对CL-20的热分解具有良好的催化活性,使CL-20的分解峰温降低1.32°C,表观分解热增加250J/g,CL-20的表观活化能由222.4kJ/mol降至181.1kJ/mol;PbSnO_3@rGO对CL-20的热分解催化效果优于r-PbSnO_3-TDI。     

Preparation and properties of thermally conductive photosensitive polyimide/boron nitride nanocomposites

A new thermally conductive photoresist was developed. It was based on a dispersion of boron nitride (BN) nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 3‐Mercaptopropionic acid was used as the surfactant to modify the BN nanoflake surface for the dispersion of BN nanoflakes in the polymer. The thermal conductivity of the composite films increased with increasing BN fraction. The thermal conductivity of the PSPI/BN nanocomposite was up to 0.47 W m⁻¹ K⁻¹ for a mixture containing 30 wt % nanosized BN filler in the polyimide matrix. Patterns with a resolution of 30 μm were obtained from the PSPI/BN nanocomposites. The PSPI/BN nanocomposites had excellent thermal properties. Their glass‐transition temperatures were above 360°C, and the thermal decomposition temperatures were over 460°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and properties of polybenzoxazole-clay nanocomposites

A novel polybenzoxazole (PBO)/clay nanocomposite has been prepared from a PBO precursor, polyhydroxyamide (PHA) and an organoclay. The PBO precursor was made by the low temperature polycondensation reaction between isophthaloyl chloride (IC) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane with an inherent viscosity of 0.5 dl/g. The organoclay was formed by a cation exchange reaction between a Na⁺-montorillonite (Na⁺-Mont) clay and an ammonium salt of dodecylamine. The PHA/clay was subsequently thermal cured to PBO/clay. Both X-ray diffraction and transmission electron microscope analyzes showed that the organoclay was dispersed in the PBO matrix in a nanometer scale. The in-plane coefficient of thermal expansion (CTE) of PBO/clay film decreased with increasing amounts of organoclay. The CTE of PBO/clay film containing 7 wt% clay was decreased by 21% compared to the pure PBO film. Both of the glass transition temperature (T_g) and the thermal decomposition temperature of PBO/clay increased with increasing amounts of organoclay. The thermal decomposition temperature and the T_g of PBO/clay containing 7 wt% clay increased to 12 and 16 °C, respectively.     

Preparation and Properties of 2,6‐Diamino‐3,5‐dinitropyrazine‐1‐oxide based Nanocomposites

With estane as binder, a new nanocomposite energetic material based on 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) was successfully prepared by the spray drying method. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and X‐ray diffraction (XRD) was employed to characterize the nanocomposite samples. The impact sensitivity and thermal decomposition properties of the nanocomposites were also measured and analyzed. The results show that the nanocomposite particles are spherical in shape and range from 1 μm to 10 μm in size. The composite is aggregated of many tiny granules with nucleus/shell structure, in which the shell thickness and crystal size of LLM‐105 are about 20 nm and 50–100 nm. The crystal type of LLM‐105 in the nanocomposite is similar to that of raw LLM‐105, however, the diffraction peaks become weaker and wider mainly due to decreasing of particle size. The nanocomposite has lower impact sensitivity and better thermal stability.     

Transparent photo‐curable co‐polyacrylate/silica nanocomposites prepared by sol‐gel process

This work prepared the highly transparent photo‐curable co‐polyacrylate/silica nanocomposites by using sol‐gel process. The FTIR and ¹³C NMR analyses indicated that during the sol‐gel process, the hybrid precursors transform into composites containing nanometer‐scale silica particles and crosslinked esters/anhydrides. Transmission electron microscopy (TEM) revealed that the silica particles within the average size of 11.5 nm uniformly distributed in the nanocomposite specimen containing about 10 wt % of Si. The nanocomposite specimens exhibited satisfactory thermal stability that they had 5% weight loss decomposition temperatures higher than 150°C and coefficient of thermal expansion (CTE) less than 35 ppm/°C. Analysis via derivative thermogravimetry (DTG) indicated that the crosslinked esters/anhydrides might influence the thermal stability of nanocomposite samples. The UV‐visible spectroscopy indicated that the nanocomposite resins possess transmittance higher than 80% in visible light region. Permeability test revealed a higher moisture permeation resistance for nanocomposite samples, which indicated that the implantation of nano‐scale silica particles in polymer matrix forms effective barrier to moisture penetration. Adhesion test of nanocomposite samples on glass substrate showed at least twofold improvement of adhesion strength compared with oligomer. This evidenced that the silica and the hydrophilic segments in nanocomposite resins might form interchains hydrogen bonds with the ? OH groups on the surface of glass so the substantial enhancement of adhesion strength could be achieved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Inhibitory effect of hydrogen bonding on thermal decomposition of the nanocrystalline cellulose/poly(propylene carbonate) nanocomposite

Biodegradable poly(propylene carbonate, PPC) is a typical noncrystalline polymer from the copolymerization of carbon dioxide (CO₂) with propylene oxide (PO). But it is easy to be degraded to propylene carbonate (PC) via backbiting route during heat process (above 170°C), which limits its application. This work reports the introduction of biodegradable nanocrystalline cellulose (NCC) which was exfoliated from microcrystalline cellulose (MCC) by acid hydrolysis into PPC, affording a biodegradable PPC/NCC nanocomposite with improved thermal decomposition temperatures (the initial decomposition temperature, T_5wt% was up to 265°C). Impressively, the thermal decomposition of PPC to PC at 200°C within 4.0 h was dramatically inhibited by introducing NCC, which was evident by ¹H NMR spectra. This could be attributed to the hydrogen bonding interaction between NCC and PPC. Moreover, the film of PPC/NCC nanocomposite had not deformed when it was heated at 110°C for 4 h. In application, such biodegradable nanocomposite is a promising disposable package material. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39847.     

Improving heat ageing and thermal properties of silicone rubber using montmorillonite clay

Heat ageing and thermal stability of a silicone rubber (SR) filled with montmorillonite clay (MMT) was investigated. Three types of rubber nanocomposites were prepared with highly exfoliated Cloisite 30B (SR/C30B), intercalated/exfoliated Cloisite Na⁺ (SR/Na⁺MMT), and highly intercalated Cloisite 20A (SR/C20A). This study showed that the SR/C30B nanocomposite exhibited excellent heat resistance in comparison to the other two nanocomposites and neat SR as revealed by higher retention strength. The thermal stability of the rubber in air was strongly dependent on the clay morphology and increased in the following order: highly intercalated/exfoliated SR/Na⁺MMT < highly intercalated SR/C20A < highly exfoliated SR/C30B. The thermogravimetric analyses of the SR/C30B nanocomposite showed a substantial increase in the final residue in comparison with the neat SR. This indicated a major improvement in the thermal stability of the rubber containing the exfoliated clay, which was also supported by the higher activation energy of decomposition measured for the nanocomposite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41061.     

Effect of radiation on creep of microplastic made from high-strength aramid fibres

The elevated radiation resistance of a microplastic based on Rusar fibres even in combined exposure to ionizing radiation and mechanical loading was demonstrated. This is probably due to the high degree of orientation of the polymer fibres, so that radiation chemical decomposition reactions are suppressed and the purely thermal effect of the radiation is experimentally recorded. Translated from Khimicheskie Volokna, No. 1, pp. 47-49, January-February, 2009.     

Comparison of Solid-State and Spray-Pyrolysis Synthesis of Yttrium Aluminate Powders

The influence of precursor characteristics and synthesis conditions on the formation of yttrium aluminum garnet, Y₃Al₅O₁₂ (YAG), was investigated using "single-source" precursors (cohydrolyzed yttrium and aluminum alkoxides and yttrium aluminum glycolates) and "multiple-source" precursors (mixtures of metal nitrates and mixtures of separately hydrolyzed yttrium and aluminum alkoxides). Phase-pure YAG was formed only in the solid-state thermal decomposition experiments. The lack of formation of YAG in all the spray-pyrolysis experiments was ascribed to the short heating times and fast heating rates, which resulted in the formation of kinetic products. In the case of the metal nitrates, an additional factor that influenced product formation was the difference in thermal reactivity of the precursors. It was concluded that the formation of complex metal oxide materials by conventional or aerosol routes is not necessarily achieved by the use of a chemically homogeneous precursor, such as a single-source precursor. It also was necessary to ensure that the precursors and intermediates have similar thermal decomposition temperatures to avoid phase segregation in the initial stages of thermal decomposition.     

轻烧菱镁矿制备高纯纳米氧化镁

以轻烧菱镁矿为原料,通过酸浸去除杂质得到纯净的含镁溶液,以草酸为沉淀剂,采用直接沉淀法制备纳米氧化镁粉体。考察了草酸和氧化镁的摩尔比、反应温度、前驱体草酸镁热分解温度及时间对纳米氧化镁粒径大小的影响。采用热重-差热分析仪、激光粒度仪、X射线衍射仪、扫描电子显微镜等对前驱体的热分解情况、产品的粒径及晶型结构进行检测。结果表明:合成的氧化镁粉体的粒径分布较窄,分散性良好,平均粒径在80nm左右,纯度达到99.1%。     

Silicon Nitride/Silicon Carbide Nanocomposite Materials: I, Fabrication and Mechanical Properties at Room Temperature

The fabrication of dense Si₃N₄/SiC nanocomposite materials that contained 2.5-30 wt% SiC via gas-pressure sintering and hot pressing was investigated. The SiC particles originated from admixed commercial SiC powders, SiCN powders produced by plasma synthesis, in situ reaction pyrolysis of carbon-coated Si₃N₄ particles, and pyrolysis of a polycarbosilazane-based SiCN precursor. Based on thermodynamic calculations, criteria for minimum liquid-phase decomposition during sintering were developed. The best sintering results were obtained for sintering cycles that observed this criteria. Materials that contained plasma-synthesized SiCN exhibited high strengths (835-995 MPa) and fracture toughness values (7.4-7.8 MPam^1/2) at room temperature. Post-sintering thermal treatments led to a strength reduction.     

Effect of Organomodified Ni-Al Layered Double Hydroxide (OLDH) on the Properties of Polypropylene (PP)/LDH Nanocomposites

This work addresses the effect of organomodified layer double hydroxide (OLDH) on the properties of PP/LDH nanocomposites prepared by melt intercalation method using a single screw extruder with maleic anhydride grafted polypropylene (PP-g-MA) as a compatibilizer. For this, Ni-Al LDH was first prepared by the co-precipitation method at constant pH using their nitrate salts. The above synthesized pristine LDH was organically modified using sodium dodecyl sulphate (SDS) by the regeneration method. The structural and thermal properties of LDH and PP nanocomposites were performed by X-ray diffraction (XRD), FTIR spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The influence of LDH loading on the mechanical and thermal properties of the nanocomposite was also investigated. The XRD results confirmed the formation of exfoliated PP/LDH nanocomposites. PP/LDH nanocomposites exhibited enhanced thermal stability relative to the pure PP. When 10% weight loss was selected as a point of comparison, the decomposition temperature of PP/LDH (5 wt%) nanocomposite was 15.3°C higher than that of pure PP. The DSC result indicated an increase in crystallization and melting temperature of the PP/LDH nanocomposites compared to pure PP. Overall, the mechanical properties of the PP/LDH nanocomposites increased with an increase in the LDH content. The maximum improvement of tensile strength, Young's modulus, flexural strength, and flexural modulus for the PP/LDH nanocomposite was found to be 11, 22.5, 28, and 22%, respectively, over neat PP. For comparison purposes, a nanocomposite with 5 wt% modified bentonite (PP/B5) was also prepared under the same operating condition and there was no significant improvement in mechanical properties (tensile strength and modulus).     

Polyurethane/clay nanocomposites reinforced with carbon and glass fibres: study of mechanical and thermal properties,and the effect of electron beam irradiation

Polyurethane (PU) nanocomposites with 0, 1, 3, 5, and 7?wt-% nanoclay contents were prepared. X-ray diffraction patterns, transmission electron microscopy images, tensile test, and thermogravimetric analysis were utilised to reveal the morphological, mechanical, and thermal-resistant properties of the prepared nanocomposites. The exfoliated structure was obtained for nanoclay contents up to 3?wt-%. Incorporation of nanoclay to the PU matrix prompted the thermal stability of the polymer. A nanocomposite filled with 3?wt-% nanoclay showed the best tensile strength in the prepared nanocomposites. Subsequently, the nanocomposite with the 3?wt-% nanoclay was reinforced with carbon and glass fibres. Reinforcement of the PU/nanoclay matrix with carbon and glass fibres significantly ameliorated the tensile properties. Finally, the effects of the electron beam irradiation on the nanocomposites and fibre-reinforced composites were studied. Irradiation with the doses up to 500?kGy enhanced the mechanical and thermal properties. However, further irradiation deteriorated the mechanical and thermal-resistant properties.     

Thermal characteristics of organoclay and their effects upon the formation of polypropylene/organoclay nanocomposites

Summary We have examined thermal characteristics of two types of organically modified montmorillonite (OMMT) with different alkylammonium cations and their effects upon the formation of PP nanocomposite, when using a maleic anhydride grafted polypropylene oligomer (maPP) as a compatibilizer. The microstructure of the composite has been characterized by X-ray diffraction (XRD) analysis, transmission electron microscopy and Fourier transform infrared spectroscopy. OMMT showed the decrease of the interlayer spacing at the processing temperature, due to the release of organic ion by thermal decomposition. Thermal characteristics of OMMTs depended greatly on the interlayer structure of OMMT. When the OMMT with small interlayer spacing and less organophilicity was used, PP composite resulted in the only partial exfoliation due to thermal decomposition of the clay layers. Received: 21 June 2000/Revised version: 11 August 2000/Accepted: 11 August 2000     

A water dispersed Titanium dioxide/poly(carbonate urethane) nanocomposite for protecting cultural heritage: Preparation and properties

A water dispersed Titanium dioxide/poly(carbonate urethane) nanocomposite was prepared by means of cold mixing of single components via sonication. The work was aimed at achieving a new material with properties suitable for eco-sustainable applications in cultural heritage as protective coating. The nanocomposite water dispersion prepared was subsequently deposited on Petri dish and, after water casting at room temperature, homogeneous, transparent, colourless film samples were obtained. TGA, DSC, DMTA, ATR-FTIR, FESEM and WAXS techniques were then applied in order to investigate the thermal and visco-elastic behaviours along with morphology and structure of the nanocomposite. Moreover, through methylorange decomposition, an azoic dye representative of environmental pollution, a photocatalytic test was set up on nanocomposite film samples assessing that the 1% (wt/wt) content of Titanium dioxide nanoparticles was able to confer self-cleaning ability. Interrelationships among structure, properties and uses in conservation of this kind of nanomaterial were appraised.