The effect of ethylene-vinyl acetate copolymer on the formation process of wax crystals and hydrates

Ethylene-vinyl acetate copolymer(EVA) as a kind of effective polymeric pour point depressant has been extensively used in the pipeline transportation of crude oil to inhibit wax deposition and improve the low temperature fluidity of crude oil. In this work, molecular dynamics simulations were performed to investigate the effect of EVA on wax-hydrate coexistence system to evaluate the application potentiality of EVA to the flow assurance of deep-sea oil-gas-water multiphase flow system. Our simulation results reveal that wax molecules gradually stretched and stacked from random coiling to a directional and ordered crystalline state during the process of wax solidification. The strong affinity of polar vinyl acetate side chains of EVA to neighboring water molecules made the EVA molecule prefer being in a curly state,which disrupted the ordered crystallization of surrounding wax molecules and delayed the solidification rate of wax cluster. In addition, it is found that EVA cocrystallized with wax molecules to form eutectic when the wax was fully solidified. The simulation results of hydrate nucleation and growth show that the EVA molecule displayed a two-sided effect on gas adsorption of wax crystals, which was the key factor that affected the nucleation and growth of hydrates in the methane-water system. The nonpolar hydrocarbon backbone of EVA increased the diffusion rate of methane and water, allowing more methane to diffuse to the surface of wax crystals, reducing the methane concentration in aqueous solutions and inhibiting the hydrate formation. On the other hand, the nonpolar vinyl acetate chains had a repulsive effect on methane, which reduced the adsorption area of methane on the eutectic surface and decreased the adsorption threshold value of the wax crystal. The excluded methane molecules would continue dissociating in the aqueous phase and participating in the nucleation and growth process of hydrates.Therefore, the probability of hydrate formation would be increased. It was worth noting that the inhibition performance of EVA on hydrate formation mainly played a significant role in the system with small wax crystal, while its hydrate promotion effect played a dominant role in the system with lager wax crystal. In summary, EVA could significantly inhibit both of the wax and hydrate deposition for the waxgas-water multiphase system with low wax content. When the wax content in the system was high, the role of EVA was mainly played in the alleviation of wax crystallization rather than the gas hydrates. The results of the present work can contribute to a better understanding of EVA on wax deposition and hydrate formation, and provide theoretical support of the potential industrial applications of EVA.

Nutrient Release Characteristics of Vinyl Chloride-Vinyl acetate Copolymers Coated SlowRelease Nitrogen Fertilizer and Its Effect on Soil Mineral Nitrogen

[Objective] The aim was to explore release characteristics of vinyl chlo- ride-vinyl acetate copolymer controlled-release N fertilizer and the effects on minerat nitrogen in soils. [Method] Vinyl chloride-vinyl acetate copolymer and hydroxyl-modi- fied VCNAc were taken as coating materials to prepare slow release fertilizer. Nutri- ent release characteristics of VC/VAc slow release fertilizer was evaluated by water immersion method and the effects of VC/VAc slow release fertilizer on mineral ni- trogen were researched by pot experiment. [Result] The release periods of VC-VAc controlled-release urea and hydroxyl-modified VC/VAc coated urea were 60 and 50 d, respectively. Furthermore, the content of ammonium nitrogen reached the peak on the 30th d and the content of nitrate nitrogen reached the peak on the 60th d in soils in treatments with VCNAc and hydroxyl-modified VC/VAc; the content of nitrate nitrogen rose again on the 120th d in the treatment with VC/VAc. In terms of wheat yield, different treatments showed insignificant differences and rice yield in the treatment with VCNAc was significantly higher than that in the treatment with hy- droxyl-modified VCNAc （P〈0.05）. [Conclusion] The release days of slow controlled- release fertilizer vary upon pot experiment method and water immersion method. Slow controlled-release fertilizer is not suitable for monoculture, due to long fertilizer efficiency, but multiple cropping would be optimal for its role to be fully exploited.

Effects of Nano-Filler on the Thermal and Fire-Resistant Properties of Ethylene-Vinyl Acetate Copolymer

Sepiolite （S9, B10, B20, B40） and boehmite have been added to an intumecent flame retardant （IFR） system to produce the halogen-free and fire-resistant ethylene-vinyl acetate copolymer （EVM） rubber. The rubber contains ammonium polyphosphate （APP） as acid source, double pentaerythritol （D-PER） as carbon source and melamine （MN） as gas source. The effects of nano-filler sepiolite and boehmite on the fire-resistant property of EVM rubber based on IFR system were investigated. The test results show that the system with nano-filler of sepiolite B10 has the best fire-resistant property. The process of smoke emission and thermal decomposition, the element composition of char surface and the micro morphology of intumecent char layer of the EVM IFR system with nano-filler were also studied by NBS chamber, thermogravimetric （TG） analysis, X- ray photoelectron spectroscopy （XPS） and scanning electron microscope （SEM）.

Sound Absorption Properties of Discarded Feathers/Ethylene Vinyl Acetate Copolymer Thermoplastic Composite Materials

The discarded feathers / ethylene vinyl acetate copolymer( EVA) thermoplastic composite materials was obtained with discarded feathers as reinforced material and EVA powders as matrix material by hot pressing method. Sound absorption properties were studied by changing mass ratio of discarded feathers and EVA,thickness of composite materials,hot pressing pressure and hot pressing temperature. It was found that the sound absorption properties of composite materials were good when the mass ratio of discarded feathers and EVA was 1: 1,thickness of composite materials was 30 mm,hot pressing pressure was 8 MPa,and hot pressing temperature was 80 ℃. Under the optimum conditions,the effect of composite density on sound absorption property was analyzed. In a certain range,the sound absorption property was enhanced with the decrease of the composite density.When the composite density was 0. 1g /cm^3, the maximum absorption coefficient was 0.96. Finally,the capillary theory was used to calculate the maximum sound absorption coefficient of discarded feathers / EVA thermoplastic composite materials. The good agreements of experimental results and calculated results proved the validity of the theoretical models.

Polyvinyl Acetate and Vinyl Acetate-Ethylene Hybrid Adhesive: Synthesis, Characterization, and Properties

The goal is to develop a hybrid IPN network of polyvinyl acetate (PVAc) and ethylene-vinyl acetate (VAE). In this research work, the vinyl acetate (VAc)/ VAE hybrid emulsion and polyvinyl acetate emulsion (PVAc) were effectively synthesized. Emulsions with various characteristics have been developed by adjusting the weight ratios between the vinyl acetate monomer and the VAE component. The impacts on the mechanical, thermal, and physical properties of the films were investigated using tests for pencil hardness, tensile shear strength, pH, contact angle measurement, differential scanning calorimetry (DSC), and viscosity. When 5.0 weight percent VAE was added, the tensile shear strength in dry conditions decreased by 18.75% after a 24-hour bonding period, the heat resistance decreased by 26.29% (as per WATT 91) and the tensile shear strength decreased by approximately 36.52% in wet conditions (per EN 204). The pristine sample’s results were also confirmed by the contact angle test. The interpenetrating network (IPN) formation in hybrid PVAc emulsion as primary bonds does not directly attach to PVAc and VAE chains. The addition of VAE reduced the mechanical properties (at dry conditions) and heat resistance as per WATT 91. Contact angle analysis demonstrated that PVAc adhesives containing VAE had increased water resistance when compared to conventional PVA stabilised PVAc homopolymer-based adhesives. When compared to virgin PVAc Homo, the water resistance of the PVAc emulsion polymerization was enhanced by the addition of VAE.

Kinetic Study of Carbonylation of Methyl Acetate to Acetic Anhydride Catalyzed by Rhodium Complex with a Ligand of Copolymer of Vinyl-acetic Ester and Acrylonitrile

The copolymer of vinyl acetic ester and acrylonitrile is used to react with [Rh（CO）2Cl]2to form a complex which can be used in the carbonylation of methyl acetate to acetic anhydride. Many factors affecting the reaction rate, catalytic activity and selectivity have been investigated. The reaction rate depends on rhodium complex and methyl iodide, and is differant from that of homogenous small molecular rhodium complex catalyst. It is revealed thatthe reaction rate is zero order in CO, first order in Rh and LiOAc, but the order in CH3I is complicated. The causes of these phenomena are discussed based on the mechanism of carbonylation of methyl acetate.

A NOVEL COPOLYMER-BOUND CIS-DICARBONYLRHODIUM COMPLEX FOR THE CARBONYLATION OF METHANOL TO ACETIC ACID AND ACETIC ANHYDRIDE

A series of porous microspheres of linear and ethylene diacrylate (M') cross-linked copolymers of 2-vinylpyridine (V) and methyl acrylate (M) reacted with tetracarbonyldichlorodirhodium to form a series of cis-dicarbonylrhodium chelate complex (MVRh and MVM 'Rh). They are thermally stable yet very reactive in the carbonylation of methanol to acetic acid, and of methanol-acetic acid mixture to acetic acid and acetic anhydride with a selectivity of 100% under relatively mild and anhydrous conditions.

NON-ISOTHERMAL CRYSTALLIZATION OF ETHYLENE-VINYL ACETATE COPOLYMER CONTAINING A HIGH WEIGHT FRACTION OF GRAPHENE NANOSHEETS AND CARBON NANOTUBES

The effect of the different geometrical dimensionality of two dimensional graphene nanosheets （2D GNSs） and one dimensional carbon nanotubes （1D CNTs） on the non-isothermal crystallization of an ethylene-vinyl acetate （EVA） copolymer at high loading （5 wt%） was studied. Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process. Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents, with a noticeably increased onset crystallization temperature of EVA. A high weight fraction of nano-fillers slowed the overall crystallization rate of composites. At the same crystallization temperatute, the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion. Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nano- fillers and polymer chains, as well as spatial restriction.

SYNTHESIS OF BLOCK COPOLYMER FROM 5,6 -BENZO-2-METHYLENE-1,3-DIOXEPANE AND METHYL ACRYLATE VIA ATOM TRANSFER RADICAL POLYMERIZATION

Poly(methyl acrylate)-b-poly(5,6-benzo-2-methylene-1,3-dioxepane) (PMA-b-PBMDO) was synthesized by two-step atom transfer radical polymerization (ATRP). Firstly, ATRP of methyl acrylate (MA) was realized using ethyl alpha-bromobutyrate (EBrB) as initiator in the presence of CuBr/2,2'-bipyridine. After isolation, poly(methyl acrylate) with terminal bromine (PMA-Br) was synthesized. Secondly, the resulting PMA-Br was used as a macromolecular initiator in the ATRP of BMDO. The structure of block copolymer was characterized by H-1-NMR spectroscopy. Molecular weight and molecular weight distribution were determined on a gel permeation chromatograph (GPC).

小空腔内EVA发泡胶带的黏结性能和发泡行为研究

采用4,4-氧代双苯磺酰肼(OBSH)作为发泡剂、以过氧化苯甲酰(BPO)作为交联剂、C9树脂作为增黏剂制备了乙烯-乙酸乙烯酯(EVA)发泡胶带,研究组分对2D发泡胶带使用性能的影响和机理。结果表明,在合适的EVA/BPO/OBSH/C9(100/3/3/40)条件下,发泡胶带能够在170℃和205℃下发泡。发泡胶带具有良好的使用性能,膨胀率超过2倍,不发生挂流,表面平整。同时,发泡胶带的拉伸强度高于5 MPa,断裂伸长率超过240%,吸水率低于5%。

低温等离子体活化氯丁橡胶和乙烯-乙酸乙烯酯共聚物及其复配改性沥青的性能

为提升胶粉改性沥青的性能,以与基质沥青质量比为11/100的氯丁橡胶(CR)和3/100的乙烯-乙酸乙烯酯共聚物(EVA)为改性剂制备了改性沥青,采用低温等离子体活化CR/EVA以进一步提升复配改性沥青的性能,研究了单一改性、复配改性和低温等离子体活化复配改性沥青(A-CR/EVA-MA)的路用性能,并使用扫描电子显微镜、原子力显微镜和傅里叶变换红外光谱分析了各改性沥青的微观机理。结果表明,各改性沥青的路用性能均有提升,总体表现为活化复配改性优于复配改性和单一改性;A-CR/EVA-MA的针入度、软化点、延度、布氏黏度及抗车辙因子较基质沥青分别提升了46%、47%、95%、253%和278%,存储稳定性也得到了进一步提高;低温等离子体活化技术增加了改性剂的比表面积和表面官能团含量,提高了改性剂对沥青中轻质组分的吸附能力,促进了CR和EVA与沥青的紧密结合,有效提升了改性沥青的路用性能。

ATH/ADP配比对EVA阻燃性能及机理转变的影响

针对氢氧化铝(ATH)在对乙烯-醋酸乙烯酯共聚物(EVA)阻燃效率低的问题,将二乙基次磷酸铝(ADP)和ATH复配,用以提高EVA阻燃性能。本研究采用垂直燃烧(UL-94)、极限氧指数(LOI)和锥形量热仪(CONE)对材料的阻燃性能进行研究。结果表明,和EVA/ATH复合材料相比,当ATH和ADP质量比为2∶1和1∶2时,垂直燃烧等级均从无等级提高到V-0级,LOI分别从34.5%提高到37.8%和42.8%。通过不同测试方法对以上两种配比的样品进行阻燃机理分析。结果表明,在ATH和ADP质量比为2:1的样品中,热分解释放的含磷化合物含量较低,而且形成的磷酸铝(AlPO4)促使炭层更致密连续,热分解产生的残炭量高于理论值,因此该配比下阻燃机理以凝聚相为主导。在ATH和ADP质量比为1∶2的样品中,炭层孔洞较多,热分解产生的残炭量低于理论值,但气相产物中出现较多含磷化合物,因此该配比下阻燃机理以气相主导。

我国高端聚烯烃产业发展现状分析

随着我国消费结构不断升级,战略新兴产业不断发展,对高端聚烯烃产品的需求也不断增加。对我国茂金属聚乙烯、茂金属聚丙烯、乙烯-醋酸乙烯树脂、超高分子量聚乙烯树脂、聚烯烃弹性体、乙烯-乙烯醇共聚树脂、环烯烃聚合物、交联聚乙烯等高端聚烯烃的产业现状、存在问题及制约因素进行了分析,对高端聚烯烃产业存在的问题进行了探讨并对未来发展提出了建议。

中高压半导电屏蔽电缆料的性能研究

采用热重分析仪、差示扫描量热仪、核磁共振波谱仪、傅里叶变换红外光谱仪、电线电缆半导电橡塑电阻测试仪和熔体流动速率仪等对中高压半导电屏蔽电缆料的基础树脂组成、聚合物分子链结构和电性能等进行剖析。结果表明:进口料和国产料虽然含有大量的炭黑填料,仍具有良好的加工流动性,且在23,90℃下的体积电阻率均较低。

乙酸乙烯酯-马来酰亚胺共聚物及其醇解物的制备

乙酸乙烯酯(VAc)的溶液聚合一般以甲醇为溶剂,但以甲醇为溶剂进行VAc与马来酰亚胺(HMI)的共聚研究目前较少报道。文中采用Finemen-Ross方法计算了VAc与HMI在甲醇中的竞聚率,分别是rHMI=4.15和rVAc=1.76×10^(-3)。之后采用饥饿投料法获得了一系列含有不同HMI含量的聚乙酸乙烯酯共聚物(PVAc/HMI),醇解后得到聚乙烯醇共聚物(PVA/HMI)。结果显示,随HMI投料比从0%(摩尔分数)增加到4%,所得PVAc/HMI的Tg上升了20%、弹性模量增加了67%,PVA/HMI的Tg上升了12%。

炭黑/十四醇基低居里温度PTC复合材料的热控性能

具有正温度系数(PTC)的导电高分子复合材料组成的自控温热敏电阻,可代替普通电阻用于加热器件,在电子设备主动控温方面具有很大优势。然而,现有PTC复合材料的居里温度(>60℃)普遍较高,在常温段工作电子设备的控温方面应用受到限制。基于此,本文以低相变温度的十四醇为相变基体,炭黑(CB)为导电粒子,乙烯-醋酸乙烯酯共聚物(EVA)为骨架,通过熔融共混和模压成型方法制备了具有低居里温度(35℃)的PTC复合材料,探究了CB质量分数对复合材料电性能和PTC性能的影响。结果显示,当CB质量分数为12%时,复合材料室温电阻率为0.5Ω·m,PTC强度高达7.0,且未出现负温度系数(NTC)效应。通过扫描电子显微镜观察了复合材料微观结构,并将复合材料电性能变化与微观结构相关联,解释了复合材料获得优异PTC性能的内在机理。此外,研究了PTC复合材料的热控行为,发现与普通电阻加热器相比,PTC复合材料作为电阻加热器具有自适应控温能力,无需外部控制系统条件下可将受控器件温度控制在常温段温度范围内并保持平衡。

EVA/PMMA杂化改性降凝剂对长庆含蜡原油流变性的影响机理

基于聚甲基丙烯酸甲酯(PMMA)微球良好的有机相容性,通过熔融共混法将PMMA微球与乙烯-醋酸乙烯酯共聚物(EVA28)降凝剂复合制备了EVA/PMMA杂化改性降凝剂;以长庆含蜡原油为研究对象,通过流变实验评价了EVA/PMMA杂化改性降凝剂对原油流变性的改善效果,利用差示扫描量热法和偏光显微镜法考察了添加降凝剂前后原油的结晶特性和蜡晶形貌变化。结果表明:与纯EVA28降凝剂相比,加入质量分数20 mg/kg EVA/PMMA杂化改性降凝剂使长庆含蜡原油的凝点从8℃降低到5℃,5℃时的黏度从40.96 mPa·s减小到35.56 mPa·s,屈服值从0.527 Pa减小到0.224 Pa。EVA/PMMA杂化改性降凝剂可以进一步降低长庆含蜡原油的析蜡点,增溶石蜡的正向作用更加显著,利于改善原油的流变性。

传感驱动一体化碳纳米管/氮化硼/乙烯-醋酸乙烯酯共聚物复合纤维的制备及其性能

为了丰富乙烯-醋酸乙烯酯共聚物(EVA)基纤维的响应方式,实现电致可逆驱动,以纳米六方氮化硼(BN)为导热填料,采用熔融纺丝工艺制备BN/EVA复合纤维,并通过溶胀-浸渍法在纤维表面包覆碳纳米管(CNTs)导电层,制得具有皮芯结构的CNTs/BN/EVA复合纤维。结果表明:CNTs与纤维基体结合紧密,在纤维表面形成了良好的导电通路,CNTs/BN/EVA复合纤维的电导率可达到58.03 S/m,且具有良好的应变传感性能,其检测范围高达281%,具有较高的灵敏度和线性响应度(在175%~281%应变范围,GF为35.19,R^(2)=99.03%),响应时间和回复时间分别为196 ms和189 ms。加捻制得的CNTs/BN/EVA复合纱线在18 V电压下可在12 s内快速升温至111.45℃,且该复合纱线在周期性电刺激条件下表现出稳定的升降温行为,实现了对电致可逆驱动应变的精准调控。

EVA/CR TPV的压缩应力松弛及其可逆回复行为

采用动态硫化法制备了基于乙烯-醋酸乙烯酯共聚物(EVA)/氯丁橡胶(CR)的热塑性硫化胶(TPV),并对其力学行为、微观结构、压缩应力松弛、可逆回复行为以及EVA/CR质量比对可逆回复不同阶段应力松弛行为的影响进行了研究。结果表明:EVA/CR TPV的压缩应力松弛行为主要受EVA相影响,CR分散相对压缩应力松弛行为的影响较小;提高热处理温度或延长热处理时间,均可显著提高TPV压缩应力松弛可逆回复程度,且当温度在EVA熔点附近时,TPV应力松弛的可逆回复程度接近100%。

EVA/NBR TPV压缩Mullins效应的研究

采用动态硫化法制备了乙烯-醋酸乙烯共聚物(EVA)/丁腈橡胶(NBR)热塑性硫化胶(TPV),系统研究了EVA/NBR TPV压缩Mullins效应。结果表明,随着EVA/NBR共混比及压缩应变的增大,TPV压缩Mullins行为趋于显著;当压缩应变一定时,首次循环加载-卸载过程中最大压缩应力、内耗和tanδ均达到最大值,而第2次加载-卸载过程中均发生大幅下降,之后下降趋势逐渐减弱。在相同应变下,EVA/NBR共混比60/40的TPV最大压缩应力、残余变形、内耗、应力软化因子和tanδ均大于共混比40/60的TPV,变化幅度较为明显。