Dynamic Mechanical Properties of Carbon Black Filled Ethylene Vinyl Acetate Rubber

Abstract

The dynamic mechanical properties of ethylene vinyl acetate (EVA) rubber filled with different loadings of carbon black and at different degrees of crosslinking were studied over a wide range of temperatures (-150° to +200°C). The loss tangent (tan δ) versus temperature plots indicated presence of different transitions. The α-transition (or the glass-rubber transition) corresponding to the maximum in tan δ value, occurred at ?17°C, which is the principal glass-transition temperature (abbreviated as T _g) of EVA rubber. The γ-transition occurred in the temperature region of ?125° to ?135°C, while the β-transition appeared as a shoulder in the temperature region of ?65° to ?75°C. Besides, there was also a high tempeature transition around +62°C which is known as liquid to liquid transition (T _1.1). Incorporation of carbon black filler did not cause any shift of T _g, while the tan δ peak values at T _g decreased sequentially with increase in filler loading. The γ- and β-relaxations were found to be insensitive to filler loading. The T _1.1 transition, however, was found to be suppressed by incorporation of carbon black filler particularly at high loading. Extent of crosslinking did not influence the T _g But, the T _1.1 transition, which was prominent with the lightly crosslinked system was found to be suppressed at high level of crosslinking. Strain dependent dynamic mechanical properties under isothermal conditions showed that the secondary structure breakdown of carbon black filler under the effect of strain amplitude is influenced by the degree of crosslinking of EVA rubber.     

Influence of Electron Beam Irradiation on the Mechanical Properties of Vegetable‐Oil‐Based Biopolymers

The influence of electron beam (EB) irradiation on the mechanical properties of biopolymers from modified linseed oil is studied. The thermoset is prepared by copolymerizing norbornenyl‐functionalized linseed oil and dicyclopentadiene (DCPD) by ring‐opening metathesis polymerization (ROMP). EB irradiation of the bulk polymer results in a substantial increase in the crosslinking density. The residual carbon‐carbon double bonds remaining after ROMP are expected to act as further crosslinking sites upon exposure to the high‐energy electrons. The increase in the crosslinking density is studied by DMA and sol/gel fraction measurements from Soxhlet extraction. Tensile testing reveals that Young's modulus and tensile strength are enhanced after EB irradiation.

     

电子束预处理对醋酯纤维降解性能的影响

利用电子束辐照对醋酯纤维进行预处理,研究电子束辐照对醋酯纤维结构、性质及生物降解性能的影响。通过扫描电镜、红外光谱、黏度测试等方法证明:电子束辐照使醋酯纤维表面产生刻蚀,纤维大分子链断裂,聚合度降低,提高了酯酶和纤维素酶对醋酯纤维的降解能力,且辐照剂量越大,处理后醋酯纤维生物降解性能越好。     

EVA增韧聚乳酸的性能研究

对乙烯-醋酸乙烯共聚物(EVA)增韧聚乳酸(PLA)体系的力学、热学和结晶性能进行了研究,并分析了增塑剂邻苯二甲酸二辛酯(DOP)对PLA/EVA增韧体系性能的影响。结果表明,PLA/EVA的质量比为80/20时,二元共混体系的力学性能最佳;PLA/EVA/DOP的质量比为80/20/8时,三元共混体系的力学性能最佳;EVA对PLA的T_g、T_m和结晶度影响不大,但DOP会使T_g和T_m降低,而结晶度得到很大提高;偏光显微镜观察结果也证实了DOP的加入有利于PLA的结晶。     

聚乳酸/乙烯-醋酸乙烯酯共聚物/碳酸钙复合材料的性能研究

采用熔融共混法制备了聚乳酸/乙烯-醋酸乙烯酯共聚物/碳酸钙（PLA/EVA/CaCO3）复合材料,利用差示扫描量热仪、X射线衍射仪、偏光显微镜、扫描电子显微镜、力学性能测试和热变形温度测试等手段,研究了EVA和CaCO3对复合材料的结晶性能、断面形貌、力学性能和耐热性能的影响。结果表明,EVA 具有增韧作用,但降低了复合材料的强度和耐热性;而CaCO3可以提高复合材料的强度、韧性、结晶性能和耐热性能;CaCO3与EVA的加入对PLA有协同增韧作用,且不改变PLA的晶型;当PLA/EVA=90/10,加入10 %（质量分数,下同）的CaCO3时,复合材料有最佳的综合性能。     

温度对碳纤维/乙烯基酯树脂导电复合材料电性能的影响

以乙烯基酯树脂作为基体,用不同质量分数的短切碳纤维制备了导电复合材料,研究了材料的电阻率与温度和伏安特性的影响。结果表明:导电复合材料的PTC转变温度随碳纤维质量分数的增加而升高;复合材料的升温曲线和降温曲线不能重合,随着碳纤维质量分数的增加,回滞环的面积变小;在0～23 V的电压范围内,复合材料的电流-电压关系在低温下符合欧姆定律,随着温度升高,材料的电流-电压关系偏离欧姆定律。     

聚丙烯/秸秆粉木塑复合材料的辐射改性及其结构与性能研究

在聚丙烯/秸秆粉(PP/CSF)复合材料加工过程中,以多官能团单体三羟甲基丙烷三甲基丙烯酸酯(TMPTMA)为辐射敏化剂,研究电子束敏化辐射对PP/CSF复合材料力学性能、吸水性能、热性能和断面微结构的影响,并对电子束敏化辐射改性PP/CSF复合材料的机理进行了初步探索。结果表明:电子束敏化辐射能够改善PP/CSF复合材料的力学性能、吸水性能、热稳定性能和界面相容性。当TMPTMA用量为8%、辐射剂量为100 kGy时,PP/CSF复合材料界面相容性良好,热稳定性提高,拉伸强度、弯曲强度和冲击强度分别提高了79%、93%和15%,吸水率降低了45%。电子束敏化辐射诱导PP/CSF复合材料发生的接枝支化和交联反应成功解决了亲水性CSF与疏水性PP之间不相容的问题,制备出综合性能优异的PP/CSF复合材料,具有广阔的应用前景。     

Mechanical,Thermal and Electrical Properties of Ethylene Vinyl Acetate Irradiated by an Electron-Beam

The effects of electron beam irradiation of (ethylene vinyl acetate) EVA containing 18% vinyl acetate was studied. The EVA sample was then irradiated by using 3 MeV electron beam machine at doses ranging from 120 to 360 kGy in air at room temperature and analyzed for mechanical, thermal and electrical properties. It was revealed by DSC analysis that the crystallinity of the electron-beam radiated EVA decreased slightly as verified by a marginal reduction in the densities and heats of melting. Thermal degradation of EVA occurred through two steps as shown by the thermogravimetric curve with maximum rates of 350 and 450°C, respectively. The results obtained from both gel content and hot set tests showed that under the irradiation conditions employed, the EVA sample cross-linked by the electron beam irradiation, and the degree of cross-linking in the amorphous regions was dependent on the irradiation dose. A significant improvement in the tensile strength of the neat EVA samples was obtained upon electron-beam radiation up to 210 kGy with a concomitant decline in elongation of break. Various electrical properties of EVA such as surface and volume resistance, breakdown voltage and dielectric constant were studied as a function of radiation dose. It was revealed that the surface resistance and volume resistivity of the EVA reaches a maximum at a 190 kGy dose of radiation. No considerable change of breakdown voltage and dielectric constant was observed with increasing irradiation dose. These studies suggest that radiation-cured EVA is more thermally and mechanically stable than pure EVA. Similarly, the results from the electrical properties revealed that surface and volume resistance are higher than pure EVA.     

短碳纤维的分散性与CFRC复合材料的力学性能

碳纤维增强水泥基复合材料(CFRC)是新发展起来的一种功能材料,制备CFRC复合材料过程中,碳纤维在水泥基体中的分散性直接影响CFRC复合材料的力学性能。借助超声波和分散剂羟乙基纤维素(HEC),实现了短碳纤维在水泥基体中的均匀分散。对所制备的CFRC复合材料的断口形貌,作了SEM观察和能谱分析;测试了试件的抗压强度和抗折强度。结果发现,水灰质量比为0.44,碳纤维均匀分散,其质量掺量为0.6%时,复合材料的抗压强度可提高20%,抗折强度提高129%。     

乙烯-乙酸乙烯酯共聚物中乙酸乙烯酯的红外光谱法测定

利用ATR技术测量样品的红外光谱,采用偏最小二乘法对所测光谱进行分析,建立了一种快速分析方法;对乙烯-乙酸乙烯酯共聚物中乙酸乙烯酯进行测定。结果表明：标准曲线线性关系良好,相关系数为0．99985,方法简单快速,结果可靠。     

PP/EVA色丝力学性能研究(英文)

研究了 PP/EVA中 EVA含量及 EVA中 VA含量对 PP色丝力学性能的影响。结果表明 :当EVA2 1添加量为 0～ 5 .0 % (质量 )时 ,色丝断裂强度及初始模量随所用色母粒种类的不同而呈现不同的变化规律 ,但均有一极大值出现 ,此时 EVA2 1添加量均小于 5 %。在色丝共混体系中 ,初始模量均在EVA2 1添加量为 2 %时出现极值。 EVA中 VA含量 ( 14 %～ 2 8% )对共混色丝力学性能的影响不同 ,当EVA添加量为 2 % ,EVA中 VA含量为 18%时 ,共混色丝有最佳的力学性能。     

乙烯-醋酸乙烯共聚物中乙烯含量测定方法研究

主要研究了乙烯-醋酸乙烯共聚物(EVA)中乙烯含量的测定方法。对样品制备、溶剂选择、体系中含水量、皂化温度、皂化时间等影响测定的主要因素进行了探讨,找到了合适的测定条件。通过与真实值进行比较,皂化法的相对误差小于0.1%。能满足EVA研究中对乙烯含量的测定要求。     

High‐Performance Pristine Graphene/Epoxy Composites With Enhanced Mechanical and Electrical Properties

High‐strength conductive pristine graphene/epoxy composites are prepared by two simple processing methods – freeze dry/mixing and solution processing. PVP‐stabilized graphene is aggregation‐resistant and allows for excellent dispersion in both the resin and final composite, as confirmed by optical microscopy and SEM images. The superior dispersion quality results in excellent nanofiller/matrix load transfer, with a 38% increase in strength and a 37% improvement in modulus for 0.46 vol% graphene loading. The composites have a very low electrical percolation threshold of 0.088 vol%. Despite the effectiveness of both methods, the freeze‐drying method is more promising and versatile enough to be used for graphene dispersion in a wide range of other composite precursors.

     

Cellulose‐Derived Carbon Fibers with Improved Carbon Yield and Mechanical Properties

The manufacture of high mechanical strength cellulose‐based carbon fibers (CFs) is accomplished in a continuous process at comparably low temperatures and with high carbon yields. Applying a sulfur‐based carbonization agent, i.e., ammonium tosylate (ATS), carbon yields of 37% (83% of theory), and maximum tensile strengths and Young's moduli up to 2.0 and 84 GPa are obtained already at 1400 °C. For comparison, the use of the well‐known carbonization aid ammonium dihydrogenphosphate ((NH₄)H₂PO₄), ADHP, is also investigated. Both the precursor and the CFs are characterized via elemental analysis, wide‐angle X‐ray scattering, Raman spectroscopy, scanning electron microscopy, and tensile testing. Thermogravimetric analysis coupled with mass spectrometry/infrared spectroscopy discloses differences in structure formation between ATS and ADHP‐derived CFs during pyrolysis.     

碳纤维/乙烯基酯树脂复合材料拉伸性能研究

研究了碳纤维进行氧化处理、铺层形式,以及紫外光照射和不同溶液介质浸泡处理等,对碳纤维/乙烯基酯树脂复合材料拉伸性能的影响。结果表明:碳纤维最佳氧化工艺为浓硝酸氧化1 h,空气氧化温度250℃,空气氧化30 min。碳纤维最佳铺层设计为[0°, 0°,45°]_2s。随紫外光照射时间增加,复合材料拉伸强度呈先增后降趋势,120 h时达最大值。溶液介质浸泡会降低复合材料的拉伸强度。温度相同溶液介质不同时,复合材料在NaOH溶液中拉伸强度降低程度最大,温度提高会加速复合材料失效老化。     

Influence of Coagulant Temperature and On-Line Drawing on the Mechanical Properties and Permeation Performance of Cellulose Acetate Hollow Fibers

Cellulose acetate (CA) ultrafiltration hollow fibers were prepared via the dry–wet spinning technique. In the spinning process, the coagulant temperature was varied, and hence the on-line draw ratio was affected. The results revealed that the maximal draw ratio increased with the increase of coagulant temperature up to 55 ^○C and then leveled off. The inner diameters, outer diameters and thickness of the hollow fiber decreased with the increase of the draw ratio. The tensile properties of the resulting hollow fibers were measured, and the breaking tensile stress increased with the increase of draw ratio. When the coagulant temperature was increased from 25 to 70 ^○C, the porosity increased, the pore size was slightly enlarged in the outer skin, the hydraulic permeability increased, and the percentage of retention R decreased. In summary, by increasing the coagulant temperature, the maximal draw ratio can be increased, and hence the mass transfer properties and the other properties of drawn CA hollow fiber can be varied.     

碳纤维/聚氨酯复合材料的制备与性能研究

以聚酯二元醇、异氰酸酯、碳纤维为主要原料,采用预聚体法制备了一系列碳纤维/聚氨酯复合材料,并对该复合材料进行了性能测试和结构表征。研究表明,复合材料的机械性能随着碳纤维长度和含量的增加出现先升高后降低的趋势。当碳纤维长度为3 mm、质量分数为1.0%时,复合材料的机械性能达到最佳值,此时其拉伸强度增加22.7%,撕裂强度增加48.1%,扯断伸长率增加5.9%。热力学分析和动态力学性能研究表明,复合材料的热分解温度提高,质量保留率提高,失重率降低,材料的玻璃化转变温度和软化温度提高,引入碳纤维后材料的耐热性提高。     

Ultra‐High‐Temperature Ceramic HfB2‐SiC Coating for Oxidation Protection of SiC‐Coated Carbon/Carbon Composites

To protect the carbon/carbon (C/C) composites from oxidation, an outer ultra‐high‐temperature ceramics (UHTCs) HfB₂‐SiC coating was prepared on SiC‐coated C/C composites by in situ reaction method. The outer HfB₂‐SiC coating consists of HfB₂ and SiC, which are synchronously obtained. During the heat treatment process, the formed fluid silicon melt is responsible for the preparation of the outer HfB₂‐SiC coating. The HfB₂‐SiC/SiC coating could protect the C/C from oxidation for 265 h with only 0.41 × 10^?2 g/cm² weight loss at 1773 K in air. During the oxidation process, SiO₂ glass and HfO₂ are generated. SiO₂ glass has a self‐sealing ability, which can cover the defects in the coating, thus blocking the penetration of oxygen and providing an effective protection for the C/C substrate. In addition, SiO₂ glass can react with the formed HfO₂, thus forming the HfSiO₄ phase. Owing to the “pinning effect” of HfSiO₄ phase, crack deflecting and crack termination are occurred, which will prevent the spread of cracks and effectively improve the oxidation resistance of the coating.     

Development of Ethylene‐Vinyl Acetate Composites Reinforced with Graphene Platelets

Composites of ethylene‐vinyl acetate (EVA) reinforced with graphene platelets are fabricated. Morphological, thermal, mechanical, electrical properties as well as moisture absorption of the composites are characterized. Transmission electron microscopy shows a good dispersion of graphene platelets in the matrix. The unidirectional orientation of graphene platelets parallel to the surface of the composites is revealed by field emission scanning electron microscopy and is validated using the Halpin–Tsai model. Tensile strength and elongation of the composites are respectively improved by 109 and 83%, after the addition of 3 wt% graphene platelets. The incorporation of 5 wt% graphene platelets enhances the char residue of the composites from 0.544% for pure EVA to 6.63% for the composites. The electrical conductivity of the composite with 3 wt% graphene platelets is two orders of magnitude higher than that of pure EVA with 10⁻¹³ S cm^–1 electrical conductivity.

     

电子束辐照对EVA/NBR复合材料结构和性能的影响

利用电子束对乙烯-醋酸乙烯共聚物(EVA)与丁腈橡胶(NBR)的共混物进行辐照交联,得到不同共混比例的EVA/NBR复合材料。考察了该复合材料的力学性能、交联度、耐油性、结晶性能及形状记忆性能,并讨论了辐照剂量和共混比例对材料性能的影响。结果表明:电子束辐照提高了EVA/NBR复合材料的力学性能和耐油性,同时降低了材料的结晶性能,这主要是由于辐照诱发了交联反应使材料内部产生了交联结构。通过控制交联度以及结晶相与NBR的比例,能够得到综合性能良好的耐油热收缩材料。