Feasibility study of friction spot welding of dissimilar single-lap joint between poly(methyl methacrylate) and poly(methyl methacrylate)-SiO2 nanocomposite

In this work, the feasibility of friction spot welding (FSpW) of a commercial poly(methyl methacrylate) (PMMA) GS grade and a PMMA 6 N/2 wt% silica (SiO₂) nanocomposite was investigated. Single-lap joints welded at rotational speeds of 1000, 2000 and 3000 rpm were produced. The analysis of the joint microstructure and material flow pattern indicated that joints could be produced using all of the tested welding conditions. However, the joint produced at 1000 rpm displayed sharp weld lines (weak links), indicating insufficient heat input, while the welds produced at 3000 rpm displayed excessive plastic deformation (bulging of the bottom plate), volumetric defects and a lack of material mixing in the welded area, associated with higher heat input. The weld produced at a rotational speed of 2000 rpm resulted in improved material mixing, which was indicated by the absence of weld lines and volumetric defects due to the more correct heat input. This welding condition was selected for further mechanical testing. Lap shear testing of PMMA GS/PMMA 6 N/2 wt% SiO₂ nanocomposite single lap joints welded at 2000 rpm resulted in an average ultimate lap shear strength of 3.9 ± 0.05 MPa. These weld strength values are equal to or better than those obtained using state-of-the-art welding techniques for PMMA materials, thereby demonstrating the potential of friction spot welding for thermoplastic nanocomposites.     

Properties of electrospun CdS and CdSe filled poly(methyl methacrylate) (PMMA) nanofibres

Electrospinning technique was used to fabricate poly(methyl methacrylate) (PMMA) fibres incorporating CdS and CdSe quantum dots (nanoparticles). Different nanoparticle loadings (2, 5 and 10 wt% with respect to PMMA) were used and the effect of the quantum dots on the properties of the fibres was studied. The optical properties of the hybrid composite fibres were investigated by photoluminescence and UV-vis spectrophotometry. Scanning electron microscopy (SEM), X-ray diffraction and FTIR spectrophotometry were also used to investigate the morphology and structure of the fibres. The optical studies showed that the size-tunable optical properties can be achieved in the polymer fibres by addition of quantum dots. SEM images showed that the morphologies of the fibres were dependent on the added amounts of quantum dots. A spiral type of morphology was observed with an increase in the concentration of CdS and CdSe nanoparticles. Less beaded structures and bigger diameter fibres were obtained at higher quantum dot concentrations. X-ray diffractometry detected the amorphous peaks of the polymer and even after the quantum dots were added and the FTIR analysis shows that there was no considerable interaction between the quantum dots and the polymer fibres at low concentration of quantum dots however at higher concentrations some interactions were observed which shows that QDs were present on the surfaces of the fibres.     

Dielectric characterization of poly(methyl methacrylate) geometrically confined into mesoporous SiO2 glasses

Characteristics of the dielectric relaxation mechanisms (γ,β,β′,α andρ) in poly(methyl methacrylate) (PMMA) and hybrids of PMMApolymerized into 5 nm SiO₂ pore matrices were studied by means of the thermally stimulated depolarization currents (TSD) technique, applied in the range 10–460 K. Low frequency relaxations (10 μHz–10 mHz) were investigated by measuring the isothermal discharging current, with the loss factorɛ”(f) determined using a new development of the Hamon method. Compared to pure PMMA, the hybrids presented a 14 to 18 degrees reduction of the TSDβ-relaxation maximum (T_β) and a drastic high temperature shift of the prominent syndiotacticα-peak. The average energy barrier for dipole (re)orientation (W) slightly decreases for both theα andβ relaxations. The latter observations, as well as the time evolution of the TSD spectra, are discussed in terms of the variation of the initiator (azobisisobutyronitrile) content and the effects of polymerization in spatial confinements (e.g. reduced monomer-to-polymer conversion at high initiator loadings and interaction effects). The shifts reflect the presence of several antagonistic mechanisms controlling the molecular dynamics of the polymeric phase. The extent of the polymer-SiO₂ hydrogen bonding interaction induces an increase of the energy barrier for the activation of the motions of the carboxymethyl lateral groups (β-process) and parts of the main chain (α-process). On the other hand, the reduction of the chain entanglements (due to the pore-directed propagation of polymerization) loosens several steric hindrances on the rotational motion of the side group, explaining the accompanying decrease of W. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

偶氮二异丁基盐酸脒引发甲基丙烯酸甲酯微球的无皂乳液聚合

采用偶氮二异丁基盐酸脒(AMPMDHC)为引发剂,用无皂乳液聚合方法制备单分散性PMMA微球,合成粒径为500nm的单分散PMMA微球的聚合条件是:MMA/H2O=20:100(m1),温度为70℃,AMPMDHC用量为0.06g,反应时间为1.5h.实验结果表明:(1)引发剂用量越多,PMMA微球粒径越小,但对微球粒径分布影响较小;(2)反应温度升高,微球粒径增大,单分散性降低;(3)微球的粒径随着水的用量增大而降低,当MMA/H2O小于1/6时,微球粒径趋于180nm.     

Chemical surface modification of poly (ethylene terephthalate) by excimer irradiation of high and low intensities

Poly (ethylene terephthalate) (PET) was modified by a KrF 248 nm excimer laser with high- (above ablation threshold) and low- (below ablation threshold) fluence. The PET surface develops usually a periodic roughness or ripples with high fluence. The roughness size is in the micron range and the surface shows signs of global melting. However, the ripple size can be reduced to sub-micron level by an irradiation of the sample below the ablation threshold with a polarized beam. The morphology of the irradiated surfaces was examined by scanning electron microscopy (SEM). Chemical surface changes of the materials were characterized by X-ray photoelectron spectroscopy (XPS). The PET modification by high fluence will normally results in the deposition of some yellow to black materials (debris), on the treated surface. The debris are ionized and from carbon rich materials which finally condense forming higher aggregates, resulting in a reduction of O/C ratio. By contrast, modification of PET surfaces by low fluence leads to an oxidation and almost no ablation is detected. The increase of oxygen concentration on low fluence modified surfaces is probably due to a subsequent reaction with atmospheric O₂ during irradiation. Our work suggests that a careful selection of laser parameters for the surface modification of polymer is of primary importance. Received: 06 November 2000 / Reviewed and accepted: 07 November 2000     

Adsorption of Cr(VI) using silica-based adsorbent prepared by radiation-induced grafting

Silica-based adsorbent was prepared by radiation-induced grafting of dimethylaminoethyl methacrylate (DMAEMA) onto the silanized silica followed by a protonation process. The FTIR spectra and XPS analysis proved that DMAEMA was grafted successfully onto the silica surface. The resultant adsorbent manifested a high ion exchange capacity (IEC) of ca. 1.30 mmol/g and the Cr(VI) adsorption behavior of the adsorbent was further investigated, revealing the recovery of Cr(VI) increased with the adsorbent feed and the equilibrium adsorption could be achieved within 40 min. The adsorption capacity, strongly depended on the pH of the solution, reached a maximum Cr(VI) uptake (ca. 68 mg/g) as the pH was in the range of 2.5–5.0. Furthermore, even in strong acidic (4.0 mol/L HNO₃) or alkaline media (pH 11.0), the adsorbent had a sound Cr(VI) uptake capacity (ca. 22 and 30 mg/g, respectively), and the adsorption followed Langmuir mode. The results indicated that this adsorbent, prepared via a convenient approach, is applicable for removing heavy-metal-ion pollutants (e.g. Cr(VI)) from waste waters.     

Poly(butylene terephthalate)/organoclay nanocomposites prepared by in-situ bulk polymerization with cyclic poly(butylene terephthalate)

The PBT/organoclay nanocomposites were prepared with cyclic poly(butylene terephthalate) oligomers and organically modified clay via in-situ bulk polymerization. Dispersion of the clay layers in the PBT nanocomposites was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability of the nanocomposites was studied by thermal gravimetric analyses (TGA). These results indicate that organoclay has been dispersed homogeneously in the PBT matrix, and the nanocomposites with intercalated-exfoliated structure were synthesized via this method. The onset degradation temperature of the nanocomposites was increased by 8-10 °C compared with the PBT homopolymer without any clay.     

Preparation and Compaction Behaviour of Poly(methyl methacrylate) Coated Iron Microparticles

The poly(methyl methacrylate)(PMMA) coatings onto surface of iron particles were electrochemically prepared and the effect on both surface structure and internal structure of the resulted material after compaction was carried out.The electrochemical polymerization treatment was performed in a fluidized bed electrolyzer using sulphuric acid solution containing potassium persulphate and methyl methacrylate(MMA).The surface topography and the microstructure of the samples were observed by scanning electron mic...     

Adhesion and degradation of hard coatings on poly (methyl methacrylate) substrates

The adhesion and time dependent crack growth behavior of polysiloxane based hard coatings on poly (methyl methacrylate) substrates were investigated. The adhesive fracture energies for different coatings were quantitatively characterized and varied between 1.4 J/m² and 22 J/m². Significant time dependent crack growth in various moist environments was observed and was consistent with a viscoelastic crack growth model. The effect of selected weathering treatments was also examined and resulted in a significant drop in coating adhesion. The coatings were analyzed using surface sensitive techniques; structural changes in the coatings resulting from various exposure doses were studied and mechanisms responsible for the observed degradation in adhesion were discussed.     

纳米SiO2对聚偏氟乙烯超滤膜的影响研究

聚偏氟乙烯铸膜液中可以加入纳米无机粒子———SiO2,制成纳米无机-有机复合膜.复合膜较纯聚偏氟乙烯超滤膜的性能有一些改善,如果纳米SiO2量合适,膜的水通量增加而截留率不变.纳米SiO2可以大大增加铸膜液的黏度,使成膜更容易.同时纳米SiO2对成膜过程也有影响,从相图看,改变了双节点的位置,对非溶剂的容纳能力降低;从DSC测试曲线得知复合膜中PVDF的结晶度增加,所以说纳米SiO2对成膜产生了延时作用.     

Effect of hydrophilic–hydrophobic balance on biocompatibility of poly(methyl methacrylate) (PMMA)–hydroxyapatite (HA) composites

The purpose of this study is to put in evidence the correlation between hydrophilic/hydrophobic balance and biocompatibility of PMMA–HA composites, in order to select the best composites for futures clinical applications. For this purpose, PMMA–HA cements with different compositions were prepared and static contact angle measurements, water absorption and gingival fibroblasts cell culture were performed and discussed.     

Poly(amidoamine)-G5 dendrimers/noble metal gold hybrid nanoparticles prepared by γ-ray irradiation

In the absence of a chemical reductant and other protective reagents, noble metal gold hybrid nanoparticles are successfully prepared by ⁶⁰Co γ-ray irradiation using fifth-generation poly(amidoamine) dendrimer with surface amine-terminated group as polymeric template. The zerovalent gold is of spherical structure and the particle size is on nanometer scale range of 3-12 nm. The size distribution of gold nanoparticles displays multidispersity. The results of FTIR show that interactions between dendrimer template and gold nanoparticle exist in intra-molecule and inter-molecule of fifth-generation poly(amidoamine) dendrimer.     

One-step preparation of poly(vinyl alcohol)-protected Pt nanoparticles through a heat-treatment method

A heat-treatment method for the preparation of well-stable, polymer-protected Pt nanoparticles in the range of 2-7 nm in diameter is demonstrated. The formation of Pt nanoparticles occurs in a single step process, carried out by heating an aqueous solution containing a poly(vinyl alcohol) polymer and H₂PtCl₆, with the use of PVA to serve as both a reducing reagent and a protective reagent. The Pt nanoparticles were characterized by UV-vis absorption spectra, transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS) and the Pt nanoparticle formation process was further investigated by in situ UV-vis experiment.     

Synthesis and characterization of thin films of poly(3-methyl thiophene) by rf-plasma polymerization

To facilitate synthesis of poly(3-methyl thiophene) thin film by RF-plasma polymerization process, suitable modifications have been done in a RF-sputtering set up. The deposition rate is found to be 3.33 nm/min. The synthesized films are characterized by FTIR, XRD, Ellipsometry, UV-Visible absorption spectroscopy and SEM. From FTIR, the formation of poly(3-methyl thiophene) has been confirmed. It is found that the synthesized polymer is cross-linked. XRD shows the amorphous nature of the prepared polymer film. The optical band gap has been estimated to be 2.14 eV from UV-visible absorption spectrum. Thickness of the polymer films has been measured to be 2000 Å by ellipsometry.     

Modification on crystallization of poly(vinylidene fluoride) (PVDF) by solvent extraction of poly(methyl methacrylate) (PMMA) in PVDF/PMMA blends

The crystallization modification of poly(vinylidene fluoride) (PVDF) was investigated for the blend films of PVDF and poly(methyl methacrylate) (PMMA). The mass crystallinity (χ_c) and further, the β-phase content (F_(β)) of PVDF, were studied for the as-prepared blend films with different mass ratios. In addition, the variations of χ_c and F_(β) were systematically probed once the PMMA component was removed from the related blend systems. DSC, FTIR and XRD measurements all indicated that 1) χ_c, F_(β) and even the content of α-phase (F_(α)) decreased with the addition of PMMA; 2) with the extraction of PMMA, both χ_c and F_(β) increased while F_(α) decreased. It is worth noting that the increase of χ_c and F_(β) depended on the relative amount of extracted PMMA (E_PMMA), i.e., the more PMMA was removed, the more χ_c and F_(β) increased. These results reveal the hindrance effect from the PMMA constituent to the crystallization of PVDF, and consequently, this restriction would be released when the PMMA was extracted.     

Hollow spherical nanocapsules of poly(pyrrole) as a promising support for Pt/Ru nanoparticles based catalyst

Poly(pyrrole) hollow spherical nanocapsules (HSNCs-PPy) were prepared and used as an efficient support matrix to PtRu nanoparticles. γ-Radiation was utilized to load PtRu nanoparticles into Ppy-HSNC matrix. The advantageous characteristics of HSNCs-Ppy/PtRu catalyst as a support matrix for loading PtRu catalysts are presented.     

改性纳米SiO2对PVdF-HFP膜形态和性能影响的研究

利用不同硅烷偶联剂改性纳米SiO2,并将改性物分别加入聚(偏氟乙烯-六氟丙烯)共聚物(PVdF-HFP)溶液中,制备成锂离子电池隔膜。FT-IR和TGA测试表明,偶联剂已成功接枝到纳米SiO2表面;SEM、拉伸、热收缩和交流阻抗测试结果显示,电池隔膜中纳米SiO2的分散性、膜的机械强度、热收缩及电导率都有明显的改善;电化学测试结果表明,含改性纳米SiO2的PVdF-HFP电池隔膜的放电比容量和循环稳定性均比含未改性纳米SiO2的电池隔膜有所提高,尤其是含γ-(甲基丙烯酰氧)丙基三甲氧基硅烷(KH570)改性SiO2的PVdF-HFP电池隔膜,各项性能均有较大的提高,其拉伸强度可达8.63MPa,离子电导率高达1.53×10-3 S/cm,放电比容量在充放电循环100次以内一直保持在142mAh/g以上。     

Preparation of poly(N-isopropylacrylamide) brush grafted silica particles via surface-initiated atom transfer radical polymerization used for aqueous chromatography

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) brushes were densely grafted onto silica surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The grafting reaction started from the surfaces of 2-bromoisobutyrate-functionalized silica particles in 2-propanol aqueous solution at ambient temperature using CuCl/CuCl₂/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as the catalytic system. Based on thermogravimetric analysis (TGA) results, the grafting amount and grafting density of PNIPAM chains on the surface of silica were calculated to be 1.29 mg/m² and 0.0215 chains/nm², respectively. The gel permeation chromatography (GPC) result showed the relatively narrow molecular weight distribution (M_w/M_n=1.21) of the grafted PNIPAAm. The modified silica particles were applied as high-performance liquid chromatography (HPLC) packing materials to successfully separate three aromatic compounds using water as mobile phase by changing column temperature. Temperature-dependent hydrophilic/hydrophobic property alteration of PNIPAAm brushes grafted on silica particles was determined with chromatographic interaction between stationary phase and analytes. Retention time was prolonged and resolution was improved with increasing temperature. Baseline separation with high resolution at relatively low temperatures was observed, demonstrating dense PNIPAAm brushes were grafted on silica surfaces.     

聚甲基丙烯酸甲酯与纳米Fe3O4的复合研究

将用共沉淀法合成的包覆油酸的Fe3O4纳米粒子,分散在甲基丙烯酸甲酯(MMA)中,采用原位聚合法制备得到PMMA/Fe3O4纳米复合材料,研究了Fe3O4含量对复合材料的玻璃化转变温度(Tg)、溶解性能以及复合材料中PMMA分子量的影响.实验结果显示:复合材料的Tg较纯PMMA有所提高,且随着Fe3O4含量的增大而增高...