The effects of gas-phase and in-depth radiation absorption on ignition and steady burning rate of PMMA

Although well studied, there are still interesting features about the ignition and steady burning rate behaviour of PMMA when heated by thermal radiation. In this contribution, the dependence on external heat flux of ignition delay time and steady mass flux of PMMA are investigated numerically. Ignition is modelled by the critical mass flux criterion. The heat transfer model includes effects of heat lost by out gassing, change of volume during degradation and absorption of radiation in both condensed and gaseous phases. Model results are compared to experimental data for both ignition delay time and quasi-steady mass flux across a range of heat fluxes from 20 to 210 kW m⁻² and the importance of both gas-phase and condensed-phase radiation absorption effects are discussed.     

From plastic-waste to H2: A first approach to the electrochemical reforming of dissolved Poly(methyl methacrylate) particles

The development of sustainable processes for the recycling of plastic is a major environmental issue to reduce the pollution by this kind of waste. The electro-oxidation of plastic wastes in electrolysers powered by renewable energies is a promising option to produce hydrogen at low temperature while diminishing the energy demand compared to Oxygen Evolution Reaction (OER). Poly (methyl-methacrylate) (PMMA) particles, a widely used polymer, were dissolved (0.1–2% wt.) in an isopropanol(IPA)/H₂O binary solvent and electro-oxidized on Pt/C-based electrodes in a liquid batch electrochemical cell at 70 °C in acidic media. Despite the dissolution strategy, polymer macromolecules partially block the accessibility of the active sites of a commercial electrode and strongly degrades its electrochemical performances mainly linked to IPA electro-oxidation. The preparation of a more porous electrode supported on carbon paper was found to strongly hinder this deactivation. Furthermore, the electrooxidation of PMMA or PMMA-derived molecules can be performed during cyclic voltammetries up to 1.4 V and chrono-amperometries at 1.4 V.     

PMMA在LIGA技术中的应用

合成了用于LIGA微细加工技术的聚甲基丙烯酸甲酯抗蚀剂,采用同步辐射装置X射线深度曝光,可得到深宽比45－90,深度大于450微米,细线宽5－10微米的良好光刻图形。     

渐变折射率塑料光纤的研究动态

介绍了渐变折射率塑料光纤 (GI- POF)的传输性能、制造方法和应用 ,简述了国内GI- POF的研究动态和展望。     

Effects of sample orientation on nonpiloted ignition of thin poly(methyl methacrylate) sheets by a laser: 2. Experimental results

The effect of the sample orientation angle on frontside (irradiated surface) ignition and subsequent backside (nonirradiated surface) flame appearance over thin poly(methyl methacrylate) (PMMA) sheets having thicknesses of 0.2 and 0.5 mm has been experimentally investigated, using a CO₂ laser as an external radiant source in quiescent normal gravity. The sample orientation angle was varied from θ=−90° (ceiling configuration) to +90° (floor configuration) at intervals of 15° under three different laser powers of 16.0, 17.3, and 26.1 W. The shortest frontside ignition delay time was observed for the ceiling configuration (θ=−90°) and frontside ignition delay time significantly varied with increase in sample orientation angle at a laser power of 16.0 W. As the laser power was increased, frontside ignition was observed at all angles and its delay time became less dependent on the sample orientation angle. The appearance of a backside flame was achieved after the formation of an open hole (due to local consumption of the sample) by two different processes: the onset of laser induced ignition over the backside sample (backside ignition) and a flame traveling from the frontside through an open hole to the backside (backside flame). The former process was observed for a limited number of cases only around the vertical configurations (−30°?θ?30°). The delay time for the appearance of backside flame tended to be longer for sample surfaces facing downward (θ°<0) than for the sample surface facing upward (θ?0°) regardless of the laser power. When the duration of laser irradiation was shortened from 10 to 4 s, as soon as the laser was shut off, the flame on the frontside immediately shrank, moved close to the sample surface, and then traveled rapidly to the backside. Therefore, the delay time of backside flame appearance (about 6 s) became longer with longer duration of laser irradiation after the onset of a frontside flame. The size of the hole (about 4 mm diameter) was large enough for the flame to travel through it, even after 4 s of laser irradiation to sample. These results indicate that the size of the hole appears to be not a critical parameter for the appearance of the backside flame.     

Electrical and thermal properties of carbon nanotubes/PMMA composites induced by low magnetic fields

Abstract

Ni particles supported on carbon nanotubes (CNTs) were dispersed in a polymethyl methacrylate (PMMA) matrix by solution blending and then cast onto an electrode to get composite films under low magnetic fields. The orientation of CNTs in the films was characterised by scanning electron microscope and optical microscope. Multimeter and high resistance meter were used to study the electrical behaviour of the nanocomposites. The glass transition temperature T _g of PMMA was determined by differential scanning calorimetry. The results show that the alignment of the CNTs dispersed in the PMMA was achieved under a low magnetic strength below 0·5 T. Because of the ferromagnetism of Ni particles, the magnetic alignment of CNTs susceptibly changed. The magnetic alignment units in this work were rod-like CNTs aggregates instead of single CNTs, which took part in the buildup of a specific CNTs network structure in PMMA matrix. The network structure played a key role in significantly improving electrical conductivity and T _g of the nanocomposites.     

Multi-methacrylated star-shaped,photocurable poly(methyl methacrylate) macromonomers via quasiliving ATRP with suppressed curing shrinkage

Novel, star-shaped multifunctional poly(methyl methacrylate) (PMMA) macromonomers with well-defined average number of pendant methacrylate groups were synthesized by copolymerizing MMA with 2-hydroxyethyl methacrylate (HEMA) via quasiliving ATRP with a tetrafunctional initiator in methanol at 10 °C, followed by methacrylation of the hydroxyl groups of the HEMA units. The resulting tailor-made poly(methyl methacrylate-co-2-methacryloylethyl methacrylate), P(MMA-co-MEMA), multifunctional macromonomers were used as cross-linking agents in photocuring of MMA, a solvent for its own polymer, and thus chemically homogeneous PMMA networks were formed in which the tetrafunctional initiator moiety provides inherent, additional branching points in the resulting cross-linked materials. This approach, even in the presence of relatively low amounts of macromonomers of ∼35–45%, provides sol-free products and up to ∼40% less polymerization shrinkage than that by curing of MMA with a conventional low molecular weight bifunctional methacrylate. These new, unique star-shaped PMMA macromonomers are potential cross-linkers in a variety of solvent-free applications where low curing shrinkage and high conversions are critical requirements, such as in several engineering materials, coatings, dental fillings and restorations, bone cements etc.     

借助ATRP法合成星型多臂氯甲基苯乙烯甲基丙烯酸甲酯共聚物

以对氯甲基苯乙烯(CMS)作为活性单体,CuCl/2,2’-联吡啶(bpy)为催化体系,用原子转移自由基聚合(ATRP)法,在120℃下,通过改变n(CuCl):n(CMS)配比,合成具有不同支化度的超支化聚对氯甲基苯乙烯(h-PC MS),分别考察了催化剂与单体的配比、溶剂极性、用量等因素对所合成的h-PCMS的组成结构、相对分子质量分布指数和转化率的影响.再分别以具有不同支化度的h-PCMS作为大分子引发剂,引发第二单体甲基丙烯酸甲酯(MMA)聚合,制得以超支化大分子h-PCMS为核,以聚甲基丙烯酸甲酯(PMMA)为臂的星型多臂共聚物h-PCMS-b-PMMA.借助红外光谱(FT-IR)、核磁共振氢谱(1H-NMR)、凝胶渗透色谱(GPC)等技术对所制得的聚合物进行表征.本研究的特点是运用先核后臂的方法来合成具有精确分子结构参数的星型多臂共聚物,为进一步深入研究其结构与性能的关系提供了物质依据,更重要的是提供了合成具有复杂但结构可控的多元共聚物的新思路.     

PMMA/EG复合材料制备及其性能研究

通过原位聚合将甲基丙烯酸甲酯(MMA)单体插入膨胀石墨(EG)层间,制备出以石墨层片为分散相的导电复合材料.用红外光谱仪和X射线衍射仪证实复合材料的合成,并讨论了石墨含量对复合材料力学性能和导电性能的影响,指出复合材料的EG含量仅为1%时,仍具有良好的导电性能和力学性能.     

有机玻璃耐磨涂层研究进展

介绍了有机玻璃耐磨涂层的几种研究路线及进展情况。