Emerging low-density polyethylene/paraffin wax/aluminum composite as a form-stable phase change thermal interface material

Thermal interface materials(TIMs) play a vital role in the thermal management of electronic devices and can significantly reduce thermal contact resistance(TCR). The TCR between the solid–liquid contact surface is much smaller than that of the solid–solid contact surface, but conventional solid–liquid phase change materials are likely to cause serious leakage. Therefore, this work has prepared a new formstable phase change thermal interface material. Through the melt blending of paraffin wax(PW) and low-density polyethylene(LDPE), the stability is improved and it has an excellent coating effect on PW. The addition of aluminum(Al) powder improves the low thermal conductivity of PW/LDPE, and the addition of 15wt% Al powder improves the thermal conductivity of the internal structure of the matrix by 67%. In addition, the influence of the addition of Al powder on the internal structure, thermal properties, and phase change behavior of the PW/LDPE matrix was systematically studied. The results confirmed that the addition of Al powder improved the thermal conductivity of the material without a significant impact on other properties, and the thermal conductivity increased with the increase of Al addition. Therefore, morphologically stable PW/LDPE/Al is an important development direction for TIMs.

Adsorption and Kinetic Study of Activated Carbon Produced from Post-Consumer Low-Density Polyethylene (LDPE) Wastes

Post-consumer polymeric wastes in form of low-density polyethylene (LDPE) can now be considered suitable as a precursor for the synthesis of low-cost activated carbon (AC). This study produced AC from LDPE using sulphuric acid (H2SO4) and potassium hydroxide (KOH) as the activating agent. The reaction conditions for pyrolysis were varied in the range of 0.50 - 2.00 M, 400°C - 500°C, and 45 - 60 minutes. Physico-chemical investigations reveal that AC yield is significantly dependent on both carbonization temperatures and time. The obtained optimum values of 446.50°C and 51.09 mins gave a yield of 24% for the base-activated carbon. The high iodine numbers obtained strongly indicate the presence of large surface area and pore volumes is further confirmed using the Scanning Electron Microscopy (SEM) analysis which reveals the presence of pores on the external surface of the carbons. Fourier Transform Infrared Technique (FTIR) analysis further shows that the synthesized compounds are purely carbon with rich oxy-gen-surface complexes on the surface which is as a result of the introduction of the chemical oxidizing agents. The produced carbons were found to have high adsorption affinity for selected inorganic ions which are: Mn7+, Co2+, and Cr6+. Adsorption isotherm results show the adsorption process to be favourable with the Langmuir isotherm parameter RL having values of <1, while the Freudlich adsorption model was found to perfectly fit the data at selected adsorbent dosages and adsorbate concentrations. The pseu-do-second-order model provides the best correlation for the kinetic analysis. The acid-activated carbon was found to have better adsorption capacities than the base-activated carbon.

EFFECTS OF COMPATIBILIZERS ON THE MECHANICAL PROPERTIES OF LOW DENSITY POLYETHYLENE/LIGNIN BLENDS

Low density polyethylene(LDPE)/lignin blends were prepared using melt blending.Two kinds of compatibilizers, ethylene-vinylacetate(EVA) which is softer than LDPE and polyethylene grafted with maleic anhydride(PE-g-MA) which is harder than LDPE were used to improve the interfacial adhesion.Scanning electron microscope(SEM) was used to investigate the dispersion of lignin in LDPE matrix.The results showed that both of the compatibilizers could improve the interaction between the low density polyethylene and l...

LOW DENSITY POLYETHYLENE/CLAY NANOCOMPOSITES MODIFIED BY ETHYLENE COPOLYMERS: EFFECTS OF FUNCTIONALIZED SEGMENTS ON MORPHOLOGY

Melt extrusion was used to prepare binary nanocomposites of ethylene copolymers and organoclay and trinary nanocomposites of low-density polyethylene （LDPE）, ethylene copolymer and organoclay. X-ray diffraction （XRD） and transmission electron microscopy （TEM） were used to analyze the structure of the clay phase and the morphology of the nanocomposites. Influences of the comonomer in the copolymer and the content of the copolymer on the morphology of the resulting nanocomposites were discussed. The binary and the trinary composites may form intercalated or exfoliated structures depending on the interaction between the copolymer and the clay layers and the content of the copolymer.

Progressive Failure Analysis of Quasi-isotropic Self-reinforced Polyethylene Composites by Comparing Unsupervised and Supervised Classifications of Acoustic Emission Data

Unsupervised and supervised pattern recognition( PR)techniques are used to classify the acoustic emission( AE) data originating from the quasi-isotropic self-reinforced polyethylene composites,in order to identify the various mechanisms in the multiangle-ply thermoplastic composites. Ultra-high molecular weight polyethylene / low density polyethylene( UHMWPE / LDPE)composites were made and tested under quasi-static tensile load. The failure process was monitored by the AE technique. The collected AE signals were classified by unsupervised and supervised PR techniques, respectively. AE signals were clustered with unsupervised PR scheme automatically and mathematically. While in the supervised PR scheme,the labeled AE data from simple lay-up UHMWPE / LDPE laminates were utilized as the reference data.Comparison was drawn according to the analytical results. Fracture surfaces of the UHMWPE / LDPE specimens were observed by a scanning electron microscope( SEM) for some physical support. By combining both classification results with the observation results,correlations were established between the AE signal classes and their originating damage modes. The comparison between the two classifying schemes showed a good agreement in the main damage modes and their failure process. It indicates both PR techniques are powerful for the complicated thermoplastic composites. Supervised PR scheme can lead to a more precise classification in that a suitable reference data set is input.

Carbon Nano Material Synthesis from Polyethylene by Chemical Vapour Deposition

Three different types of Polyethylene family, High Density Polyethylene, (HDPE), Low Density polyethylene (LDPE) and Linear Low Density polyethylene (LLDPE) polymers having different molecular weight and density;were pyrolyzed in the temperature range of 550°C - 1050°C under H2, N2 and Ar gases. Taguchi Optimization technique was applied to find out the best operating conditions to get maximum yield of carbon nano material (CNM). For Taguchi op- timization, experimental set up was done in two different temperature ranges i.e. 550°C - 750°C and 850°C - 1050°C. CNMs synthesized were characterized by SEM, TEM, Micro Raman and XRD analysis. HDPE was found to yield maximum CNM. Its pyrolysis at 750°C under hydrogen atmosphere for 2h gave carbon nano beads and some carbon nano tubes. Whereas under same conditions at 1050°C more multi wall carbon nano tubes (MWCNT) were produced, with some carbon nano beads. XRD data confirmed the graphitic nature of carbon-nanotube. The intensities of G-band and D-band of Raman spectra suggested that CNM has more defect sites and spectra were similar for CNM obtained in both the temperature ranges. The TGA analysis of CNM obtained at 550°C - 750°C, indicated that they are not amor- phous carbon and CNM obtained at 850°C - 1050°C decomposed at 624°C - 668°C;suggesting that CNT synthesized at this temperature range were more crystalline than what was obtained at the 550°C - 750°C.

LDPE轻型重包装料2426F的开发

依据轻型重包装料产品指标,根据通用料的生产情况确定了最佳生产工艺参数,开发出了轻型重包装料2426F。分析结果显示拉伸断裂应力、拉伸断裂应变、雾度均在指标范围内,产品质量合格。用户反馈表明,该产品符合2426F使用标准。

Sorption kinetics of parent and substituted PAHs for low-density polyethylene（LDPE）:Determining their partition coefficients between LDPE and water(KLDPE) for passive sampling

Low-density polyethylene(LDPE)has been widely used as a sorbent for passive sampling of hydrophobic organic contaminants(HOCs)in aquatic environments.However,it has seen only limited application in passive sampling for measurement of freely dissolved concentrations of parent and substituted PAHs(SPAHs),which are known to be toxic,mutagenic and carcinogenic.Here,the 16 priority PAHs and some typical PAHs were selected as target compounds and were simultaneously determined by gas chromatography–mass spectrometer(GC–MS).Some batch experiments were conducted in the laboratory to explore the adsorption kinetics of the target compounds in LDPE membranes.The results showed that both PAHs and SPAHs could reach equilibrium status within19–38 days in sorption kinetic experiments.The coefficients of partitioning between LDPE film(50μm thickness)and water(KLDPE)for the 16 priority PAHs were in good agreement with previously reported values,and the values of KLDPEfor the 9 SPAHs are reported in this study for the first time.Significant linear relationships were observed,i.e.,log KLDPE=0.705×log KOW+1.534 for PAHs(R^2=0.8361,p<0.001)and log KLDPE=0.458×log KOW+3.092 for SPAHs(R^2=0.5609,p=0.0077).The selected LDPE film was also proven to meet the condition of"zero sink"for the selected target compounds.These results could provide basic support for the configuration and in situ application of passive samplers.

纳米填充浓度对LDPE/Silica纳米复合介质中空间电荷行为的影响

为研究纳米颗粒填充浓度对复合介质内部空间电荷特性的影响,以低密度聚乙烯(low-density polyethylene,LDPE)为基料,纳米二氧化硅(Silica)为填充颗粒,制备了浓度在0%～5%范围的纳米LDPE/Silica复合介质,并测试了复合介质的准稳态直流电导和空间电荷分布。当LDPE内填充不同浓度的纳米silica后,复合介质内部的平均体空间电荷密度均得到有效抑制,且其平均衰减速度随填充浓度的升高而下降,但复合介质的准稳态直流电导在填充浓度低于0.5%时比纯LDPE时要大,当填充浓度高于0.5%时,准稳态直流电导随着填充浓度的升高而快速下降。结果表明试样内部的空间电荷分布存在3种趋势:当纳米silica填充浓度为0%～0.1%时,试样内表面侧的异极性空间电荷量随填充浓度升高而下降;当填充浓度为0.5%～2%时,试样内表面侧积累同极性电荷,并随填充浓度升高而增大;当填充浓度高于2%时,同极性空间电荷量下降。最低空间电荷密度和准稳态直流高场电导对应的纳米填充浓度分别为0.5%和5%,表明在应用纳米颗粒对聚合物的绝缘性能改良时,为获得最佳的介电性能,应根据实际需求来选择适当的填充浓度。

MPE/LLDPE/LDPE共混熔体的流变学

研究了不同比例共混的茂金属聚乙烯 (MPE)、线性低密度聚乙烯 (LL DPE)及高压聚乙烯 (2 0 %固定质量配比的 LDPE)熔体的流变学行为 ,讨论了共混物组成、剪切速率和剪切应力以及温度对熔体流变曲线、熔体粘度和膨胀比的影响 ,为 MPE的共混改性加工提供了理论依据。不同共混比的熔体均为假塑性流体 ,共混熔体的假塑性随 LDPE/ LL DPE的增多而增强。共混熔体的转变应力和非牛顿指数随LDPE/ LL DPE的增加而降低 ,对加工的敏感性提高 。

纳米粒子分散性对SiO_2/LDPE纳米复合介质直流介电性能的影响

纳米复合介质的介电性能与纳米粒子分散性密切相关。选取两种具有不同分散能力的纳米Si O2粉末分别与低密度聚乙烯(low density polyethylene,LDPE)复合,研究了纳米粒子分散性对纳米复合介质的直流电导电流、空间电荷及直流击穿强度特性影响。应用原子力显微镜的静电力模式观察了Si O2/LDPE纳米复合介质的表面电势分布。结果表明:改善纳米粒子分散性对于抑制SiO 2/LDPE复合介质的直流电导电流,提高空间电荷抑制能力及直流击穿强度有积极影响。通过静电力分析证实了SiO 2/LDPE纳米复合介质中,Si O2粒子与基体聚合物界面存在荷电分布,该荷电分布可对载流子迁移起散射作用,从而降低直流电到电流和提升击穿强度。通过引入观测的界面核电区厚度参数,理论计算证实了改善纳米粒子分散性可增加单位体积荷电域所占的体积分数,且被认为是高分散型Si O2/LDPE纳米复合介质介电性能显著提升的主要原因。

退火条件对LDPE空间电荷特性的影响研究

使用冷却速率不同的3种退火方法制备了不同微观形态的LDPE薄膜,对薄膜试品进行了显微观测, 并运用傅立叶红外分析对3种试品的结晶度进行了比较,同时使用PEA空间电荷测量技术对不同电场下这3种 试品的空间电荷分布进行了观测,并基于结晶度和微观形态对LDPE空间电荷特性做了讨论．研究结果表明施 加电场撤压后,高速冷却试品比低速冷却试品和正常冷却试品积聚更多的空间电荷,而随着撤压时间的增加, 低速冷却试品中积聚的空间电荷衰减得最快．

金属填充LDPE薄膜电磁屏蔽性能研究

通过向聚合物低密度聚乙烯（LDPE）中填加导电填料不锈钢纤维和镍粉,制备成了LDPE-Ni/不锈钢纤维电磁屏蔽复合薄膜.实验研究了金属填充聚合物LDPE作为电磁屏蔽复合膜的性能,分析了金属填料的加入对复合膜电磁性能、导电性能和力学性能的影响机理.结果表明,该薄膜对800 MHz以下的低频段电磁波有良好的屏蔽效能,屏蔽值为25-30 dB;“渗滤阈值”为15%-20%;材料具有较强的吸波功能;当不锈钢纤维和镍粉的质量分数为16%时,复合材料达到最大拉伸强度15 MPa.

LDPE/石墨复合材料的制备和性能

选用电导率、导热系数高的石墨(普通鳞片石墨FG、可膨胀石墨KP35、膨胀石墨EG35)对低密度聚乙烯(LDPE)进行填充改性,采用钛酸酯偶联剂NDZ101对石墨进行表面处理,提高石墨与聚合物基体的界面相互作用,制备出力学性能、导电、导热等综合性能优良的LDPE/石墨复合材料。结果表明:石墨的填充大大改善了聚乙烯的导电、导热和耐热性能,当石墨含量达20%时(文中的各种元素含量均指质量分数),LDPE/KP35的电导率达到1.91×10-7S/m,拉伸强度较LDPE有小幅提高,可作为导热抗静电材料推广应用。

LDPE与HDPE共晶问题的研究 Ⅳ 熔融共混物的热行为

应用差示扫描量热法，考察了几种不同牌号的ＬＤＰＥ与ＨＤＰＥ配伍的熔融共混物的热行为．发现熔融共混物的热行为特征与溶液共混共沉物的不同，表明不同品种ＰＥ共混物的晶相能否形成共晶与其共混方法有关。

EG填充无卤阻燃型LDPE复合薄膜阻燃性能研究

为了改善聚合物低密度聚乙烯(LDPE)薄膜的阻燃性能,通过向其中添加膨胀型阻燃剂聚磷酸铵(APP)/季戊四醇(PER)和可膨胀石墨(EG),制备了无卤阻燃型低密度聚乙烯复合薄膜。实验研究了膨胀阻燃剂填充聚合物LDPE作为阻燃复合薄膜的性能,分析了膨胀阻燃剂的加入对复合膜阻燃性能、残重率和力学性能的影响机理。研究发现,该新型配方中的EG和APP/PER对复合薄膜的阻燃性能具有协同作用,当配方中APP/PER/EG的填充量达到30%质量分数(APP∶PER∶EG∶LDPE质量比16∶8∶6∶100)时,薄膜材料的氧指数可达到27.5%;与纯LDPE薄膜相比,阻燃薄膜的氧指数提高了10.3%,改善了阻燃效果。

芴酮引发丙烯酸两步接枝LDPE膜表面改性的研究

采用两步接枝方法,研究了芴酮(FL)引发丙烯酸(AA)在低密度聚乙烯(LDPE)膜表面的接枝聚合过程,探讨了单体浓度、聚合温度等因素对表面接枝的影响。结果表明:在单体质量分数为5%～20%,聚合温度为70～90℃范围内,增大单体浓度、提高聚合温度,有利于接枝反应的进行。采用称量法、表面水接触角测定法、红外光谱分析等手段对表面接枝膜进行了表征,结果表明丙烯酸被成功地引入到LDPE膜表面,接枝率最高达到8.24%,改善了LDPE膜表面的亲水性。

纳米ZnO/LDPE食品包装膜及食品模拟物中ZnO含量的测定

建立了微波消解/电感耦合等离子体原子发射光谱(inductively coupled plasma atomic emission spectrometer,ICP-AES)及电感耦合等离子质谱仪(inductively coupled plasma mass spectrometer,ICP-MS)对纳米氧化锌/低密度聚乙烯(纳米Zn O/LDPE)薄膜及食品模拟物中Zn O含量的检测方法。根据EU10/2011选择30 g/L乙酸及超纯水为食品模拟物,将纳米Zn O/LDPE薄膜在40℃下浸泡10 d,测定食品模拟物中的Zn O含量。结果表明:Zn在0.03~100μg/L及0.1~5 mg/L的浓度范围内线性关系良好,相关系数不低于0.999 8,在低、中、高3个水平进行加标实验,加标回收率在91.2%~110.2%之间,相对标准偏差(RSD,n=6)为0.3%~6.8%,方法在消解液、30 g/L乙酸及超纯水的检出限(LOD)分别为0.015 mg/L,0.03 mg/L及0.03μg/L,方法的定量限(LOQ)分别为0.05 mg/L,0.1 mg/L及0.1μg/L,方法精密度好,灵敏度高,定性定量准确。采用该方法测得,实验室3种自制纳米复合薄膜中Zn O含量分别为(4.71±0.19),(9.20±0.49)及(12.87±0.33)g/kg,在40℃10 d后,3%乙酸(w/v)食品模拟物中Zn O的含量分别为(2.35±0.02),(3.54±0.01)及(4.12±0.35)mg/kg,在水食品模拟物中Zn O的含量分别为(24.65±0.68),(24.80±1.25)及(45.85±0.32)μg/kg。

LDPE无卤化阻燃处理技术进展

主要综述了近年来国内外LJPE无卤化阻燃处理技术,特别对磷系类及无机系类阻燃处理技术作了较详细的介绍。