熔体拉伸PE–HD和PE–LLD薄膜的制备及性能

以高密度聚乙烯(PE–HD)和线型低密度聚乙烯(PE–LLD)树脂为原料,采用转矩流变仪,借助熔体拉伸法制备了具有取向结构的PE–HD膜和PE–LLD膜。利用偏光显微镜、傅立叶变换红外光谱、差示扫描量热、小角激光散射及力学性能测试分析不同熔体拉伸速率下PE–HD膜和PE–LLD膜的结构与性能变化情况。结果表明,熔体拉伸速率越高,PE–HD膜和PE–LLD膜的相对取向度越高,快速拉伸PE–HD膜和PE–LLD膜的相对取向度分别为2.043和1.556;熔体拉伸速率对PE–HD膜和PE–LLD膜的结晶温度影响不大,两种膜具有显著的结晶性,PE–HD膜的结晶性更好;随熔体拉伸速率的提高,PE–HD膜和PE–LLD膜的拉伸屈服应力和拉伸弹性模量提高,断裂伸长率降低,总体上看,PE–LLD膜的断裂伸长率较PE–HD膜高,而拉伸强度较PE–HD膜低。     

高密度聚乙烯/植物纤维复合材料性能研究

采用双螺杆挤出机制备了一系列的高密度聚乙烯(PE–HD)/木粉(WF)和PE–HD/秸秆粉(SF)复合材料,研究了马来酸酐接枝聚乙烯(PE-g-MAH)及丙烯酸酯接枝聚乙烯(PE-g-AE)的用量对复合材料的拉伸性能、冲击性能和熔体流动速率(MFR)的影响,并对PE–HD/WF与PE–HD/SF复合材料的性能进行了比较。结果表明,PEg-MAH和PE-g-AE均可增韧PE–HD/WF和PE–HD/SF复合材料,PE-g-AE的增韧效果总体上优于PE-g-MAH;PE-g-MAH和PE-g-AE降低了PE–HD/WF复合材料的拉伸强度,但对PE–HD/SF复合材料有一定的增强作用;PE-g-MAH和PE-g-AE可在一定程度上提高PE–HD/WF复合材料的MFR,而PE–HD/SF复合材料的MFR总体上随PE-g-AE用量增加而增大,随PE-g-MAH用量增加而减小;在PE-g-AE作用下,除拉伸强度外,PE–HD/SF复合材料的冲击强度、断裂伸长率、MFR总体上均高于PE–HD/WF复合材料;当PE-g-AE的用量为其与PE–HD总质量的5%时,PE–HD/SF复合材料的综合性能最佳。     

云母粉改性高密度聚乙烯的汽油阻隔性

以片状云母粉为阻隔改性剂,与高密度聚乙烯(PE–HD)熔融共混,以改善其对汽油的阻隔性,考察云母粉形貌、含量等因素对PE–HD/云母粉复合材料阻隔性、熔体流动性以及力学性能的影响。结果表明,云母粉可显著提高复合材料对汽油的阻隔性,但熔体流动速率(MFR)与断裂伸长率降幅明显,高径厚比的云母粉对复合材料的汽油阻隔性提升更为显著,但径厚比过大不利于阻隔性的进一步提升,并会导致材料MFR和断裂伸长率进一步下降;当云母粉含量开始增加时,复合材料的汽油阻隔性明显提升,拉伸强度与缺口冲击强度上升,而MFR和断裂伸长率下降,当裂纹发展方向垂直于云母片面积方向时,缺口冲击强度提高更为显著;随着云母粉含量继续增加,复合材料的汽油阻隔性趋于稳定,拉伸强度与缺口冲击强度却明显下降。当径厚比为180的云母粉质量分数为30%时,复合材料具有最佳的综合性能,其汽油浸泡后的拉伸强度保持率显著高于纯PE–HD。     

基于冲压试验的聚乙烯力学性能预测

通过对5种不同曲率半径的高密度聚乙烯(PE?HD)圆棒试样进行单轴拉伸试验,重点分析了曲率半径对工程应力?位移曲线的影响;同时对PE?HD平板试样进行冲压试验,分析了压头直径和冲压速度对载荷?位移曲线的影响;建立了3种基于冲压载荷预测PE?HD单轴屈服应力的经验公式.结果表明,同一拉伸速度下,屈服强度随曲率半径的减小而...     

双峰PE生产工艺对其结晶行为和力学性能的影响

采用高温液相凝胶渗透色谱仪、广角X射线衍射仪和拉力机,研究了双峰聚乙烯(PE)生产中环管反应器和气相反应器的工艺参数对双峰PE产品的结晶行为和力学性能的影响。结果表明:环管反应器聚合产物的结晶度随停留时间的延长而减小,气相反应器产物的结晶度随n(H2)/n(C2H4)下降、n(1-C4H8)/n(C2H4)增大和床层分配率增加而减小,双峰PE的拉伸屈服应力和拉伸弹性模量随其结晶度和相对分子质量增加而减小。     

工艺参数对微注射成型等规聚丙烯拉伸性能的影响

选用等规聚丙烯为实验材料,基于正交实验设计方法进行微注射成型实验,制备了微注塑拉伸试样,并选取拉伸弹性模量和拉伸屈服应力作为力学性能指标。采用直观分析和方差分析法对拉伸实验的结果进行分析,研究工艺参数对厚度为1.0 mm和0.2 mm试样拉伸性能的影响规律及重要性,并分析了尺度效应对试样力学性能的影响。结果表明,微注塑实验的拉伸弹性模量和拉伸屈服应力都随着试样尺寸的减小而增大,且不同试样尺寸下,各工艺参数对拉伸弹性模量和拉伸屈服应力的影响规律和重要性也不同。对于厚度为1.0 mm的试样,其拉伸弹性模量受保压压力的影响最大,随保压压力增加呈现先增后减的趋势;其屈服应力受保压时间的影响最大,随保压时间增加呈现先增后减的趋势。对于厚度为0.2 mm的试样,拉伸弹性模量和拉伸屈服应力受熔体温度的影响最大,且两者均随着熔体温度的升高而减小。     

玄武岩纤维增强高密度聚乙烯的力学性能

玄武岩纤维(BF)未经改性处理和经硅烷偶联剂(KH–550和KH–570)进行处理后,添加到高密度聚乙烯(PE–HD)基体树脂中,增强PE–HD的力学性能,用傅立叶变换红外光谱和扫描电子显微镜对硅烷偶联剂处理的BF进行表征,同时,用SEM观察BF增强PE–HD复合材料的拉伸断面。结果表明,随着未经改性处理BF添加量增加,PE–HD复合材料的拉伸强度、弯曲强度逐渐提高,当添加量达到30%时,拉伸强度达到45.5 MPa,提升79.1%;弯曲强度达到41.3 MPa,提升118.9%。经KH–550和KH–570处理的BF添加量达到20%时,PE–HD复合材料的拉伸强度均达到45 MPa以上,其后随着BF添加量继续增加,拉伸强度变化不大,而弯曲强度随BF添加量的增加逐渐增大。当BF添加量达到30%时,BF改性与否对PE–HD复合材料的力学性能的影响不大。当改性BF添加量为5%~15%时,KH–550改性的PE–HD复合材料的力学性能较KH–570改性的高;当改性BF添加量为20%,25%时,KH–570改性的PE–HD复合材料的力学性能较KH–550改性的高。     

热拉伸过程中PE–UHMW/PE–HD共混纤维的晶体结构演变

将超高分子量聚乙烯(PE–UHMW)与高密度聚乙烯(PE–HD)按照质量比为6︰4进行共混熔融纺丝,并对初生丝进行高倍热拉伸制得PE–UHMW/PE–HD共混纤维。利用广角X射线衍射、差示扫描量热、声速取向试验等方法研究了PE–UHMW/PE–HD共混纤维在热拉伸过程中的晶体结构演变过程。研究显示,随着热拉伸过程的进行,纤维的分子链沿纤维的轴向取向度逐渐增加,熔融峰温度逐渐升高,结晶度逐渐增加;沿径向的晶粒尺寸逐渐减小,而沿轴向的晶粒尺寸逐渐增加,即形成了更细长的晶粒;晶体的取向度逐渐增加。当拉伸倍数由1增大至6时,上述现象变化显著,当拉伸倍数由9增至15时,上述现象变化缓慢。与PE–HD共混后的纤维结晶度、晶体取向度和分子链取向度更高,晶粒更加细长。     

MPEG对PE-HD／POM共混材料性能的影响

为改善高密度聚乙烯(PE–HD)／聚甲醛(POM)体系的相容性,采用聚乙二醇单甲醚(MPEG)作为相容剂,研究MPEG对PE–HD／POM共混材料性能的影响。结果表明,MPEG的加入提高了PE–HD／POM共混材料的力学性能,实验范围内随着MPEG用量的增加,共混材料的拉伸强度和冲击强度均不断提高;扫描电子显微镜、差示扫描量热及红外光谱分析表明,MPEG的加入改善了共混材料的相容性。     

低密度聚乙烯/聚乳酸共混物性能的研究

利用熔融成型法制得不同聚乳酸(PLA)质量分数的低密度聚乙烯/聚乳酸(PE–LD/PLA)共混物,并对PE–LD/PLA共混物的结构和性能进行研究。结果表明,共混物中PLA相与PE–LD相之间没有发生化学反应,它是PLA与PE–LD的一种简单混合物。共混物中的PLA含量对其力学性能和亲水性均有很大影响。随着PLA含量的增加,共混物的断裂伸长率逐渐降低而拉伸强度和拉伸弹性模量逐渐增大,共混物的亲水性增加,且随着降解时间的增加,共混物的断裂伸长率轻微增加而拉伸强度和拉伸弹性模量小幅度降低,这些现象均与PLA是一种强度高但柔韧性较差的亲水性高分子材料有关。     

高密度聚乙烯管热熔焊接接头本构模型研究

采用实验方法研究高密度聚乙烯（PE?HD）热熔焊接接头区域的材料性能与管材本体的差异。按照ISO 21307标准方法形成热熔焊接接头后,去除内外卷边,设计接头取样方式并改进拉伸试样。通过不同应变率下管材和焊接接头的单轴拉伸试验,使用一种新的本构分析方法与Suleiman方法研究其本构模型差异,得到了模型参数随应变率变化的非线性关系。对比模型预测结果和试验结果,验证了非线性拟合本构模型的有效性和合理性,同时该模型可预测低应变率下（准静态）的应力应变曲线。结果表明,PE?HD焊接区域的弹性模量和屈服应力优于管材,但差别不明显。     

Thermal and strain rate sensitive compressive behavior of polycarbonate polymer - experimental and constitutive analysis

The mechanical behavior of polycarbonate (PC) polymer was investigated under the effect of various temperatures and strain rates. Characterization of polymer was carried out through uniaxial compression tests and split Hopkinson pressure bar (SHPB) dynamic tests for low and high strain rates respectively. The experiments were performed for strain rates varying from 10 ^?3 to 10³ and temperature range of 213 to 393 K. By conducting these experiments, the true stress–strain (SS) curves were obtained at different temperatures and strain rates. The results from experiments reveal that the stress–strain behavior of polycarbonates is different at lower and higher strain rates. At higher strain rate, the polymer yields at higher yield stress compared to that at low strain rate. At lower strain rate, the yield stress of the polymer increases with the increase in strain rate while it decreases significantly with the increase of temperature. Likewise, initial elastic modulus, yield and flow stress increase with the increase in strain rate while decreases with the increase in temperature. The yield stress increases significantly for low temperature and higher strain rates. On the basis of experimental findings, a phenomenological constitutive model was employed to capture the mechanical behavior of polymer under temperature and loading rate variations. The model predicted the yield stress of polymer at varying strain rate and temperature also it successfully predicted the compressive behavior of polymer under entire range of deformation.     

微流道中聚合物熔体的弹性特性研究

采用双机筒毛细管流变仪,以直径1.5 mm的口模作为宏观流道、直径0.5 mm的口模作为微观流道、直径1.0 mm的口模作为临界参考,通过毛细管入口压力降和聚合物熔体应力松弛时间研究了微尺度下聚甲基丙烯酸甲脂（PMMA）、聚苯乙烯（PS）、高密度聚乙烯（PE-HD）及聚丙烯（PP）4种聚合物熔体的弹性特性,并讨论了在口模直径为0.5 mm条件下温度对入口压力降和应力松弛时间的影响。结果表明,微流道中4种聚合物熔体的入口压力降与应力松弛时间与宏观流道相比均有增大的趋势,且流道尺寸越小,增大趋势越明显;随着剪切速率的增大,4种聚合物熔体的入口压力降增大,但在高剪切速率下,增大趋势变缓;微流道中,随着温度的提高,4种聚合物熔体的入口压力降降低,应力松弛时间变短。     

核电站用PE-HD管水压试验压力变化规律研究

基于高密度聚乙烯（PE-HD）松弛模量方程、管道长时力学模型和水的状态方程,研究了PE-HD管水压试验压力变化规律,讨论了管道端部约束类型、保压时间和温度的影响。研究发现,约束类型对压力变化基本无影响;增加保压时间能有效降低压降和压降速率,提高试验的稳定性;随着温度的升高,PE-HD管水压试验的压降减小,温度和压降大致呈线性关系。     

The effect of time and temperature on the mechanical behavior of epoxy composites

A crosslinked epoxy resin consisting of a 60/40 weight ratio of Epon 815 and Versamid 140 and composites of this material with glass beads, unidirectional glass fibers and air (foams) were tested in tension, compression and flexure to determine the effect of time and temperature on the elastic properties, yield properties and modes of failure. Unidirectional continuous fiber-filled samples were tested at different fiber orientation angles with respect to the stress axis. Strain rates ranged from 10^?4 to 10 in./in.-min and the temperature from ?1 to 107°C. Isotherms of tangent modulus versus strain rate were shifted to form master modulus curves. The moduli of the filled composites and the foams were predictable over the entire strain rate range. It was concluded that the time-temperature shift factors for tangent moduli and the time-temperature shift factors for stress relaxation were identical and were independent of the type and concentration of filler as well as the mode of loading. The material was found to change from a brittle-to-ductile-to-rubbery failure mode with the transition temperatures being a function of strain rate, filler content, filler type and fiber orientation angle, indicating that the transition is perhaps dependent on the state of stress. In the ductile region, an approximately linear relationship between yield stress and log strain is evident in all cases. The isotherms of yield stress versus log strain rate were shifted to form a practically linear master plot that can be used to predict the yield stress of the composites at any temperature and strain rate in the ductile region. The time-temperature shift factors for yielding were found to be independent of the type, concentration and orientation of filler and the mode of loading. Thus, the composite shift factors seem to be a property of the matrix and not dependent on the state of stress. The compressive-to-tensile yield stress ratio was practically invariant with strain rate for the unfilled matrix, while fillers and voids raised this ratio and caused it to increase with a decrease in strain rate. The yield strain of the composites is less than the unfilled matrix and is a function of fiber orientation and strain rate.     

Strain rate dependence of tension and compression behavior in nano-polycrystalline vanadium nitride

We performed molecular dynamics (MD) uniaxial tension and compression simulations of nano-polycrystalline (npc) vanadium nitride (VN) with different strain rates to investigate strain rate effects and tension-compression asymmetry in npc VN. The Zener's familiar anisotropy index A of the polycrystalline VN model is 0.957, very closed to 1.0, demonstrating its elastic isotropy. The Young's modulus increases with the increase of strain rate. The yield strain, yield stress and flow stress increase in power form with the increase of strain rate. As the strain rate varies in the range between 5E8 and 1E9 s⁻¹, strain rate effect becomes insignificant, and the corresponding loading can be regarded as quasistatic or low strain rate loading. Tension-compression asymmetry was observed and analyzed systematically. The elastic tension-compression asymmetry should be ascribed to the higher friction in compression, the asymmetry of interatomic potential, and the effect of cutoff distance in a MD simulation. While the plastic tension-compression asymmetry should mainly result from the different kinds of atomic interaction, intergranular fracture and dislocation glide. No distinct grain boundary sliding was found.     

Catalytic cracking of 1-butene to propylene by Ag modified HZSM-5

Silver modified HZSM-5 (AgHZ) zeolite catalysts were prepared by ion exchange method and their catalytic properties in the 1-butene cracking reaction were measured. The catalysts were characterized by infrared spec-troscopy with pyridine adsorption (Py-IR), N2 adsorption and X-ray diffraction (XRD). The effects of Ag loading and steaming treatment on catalytic performances were studied. It is found that the activity of HZSM-5 (HZ) cat-alyst significantly decreases with the steaming time, whereas AgHZ catalysts show stable activity in the steaming time of 24–48 h and their activities increase with the Ag loading. When the steaming time is 24–48 h, the yield of propylene over HZ catalyst significantly decreases, whereas it is stable over AgHZ catalysts. The AgHZ catalysts with Ag loadings of 0.28%–0.43%(by mass) show similar propylene yields (~30%), which are higher than that over the AgHZ catalyst with a Ag loading of 0.55%(by mass). These results indicate that the steam-treated AgHZ catalysts with optimum Ag loadings have higher yield of propylene and are more stable than the steam-treated HZ catalyst. The regeneration stability measurement in butene cracking also shows that the AgHZ catalyst steam-treated under a suitable condition has better stability than the HZ catalyst.     

往复荷载下含孔洞缺陷衬砌混凝土的力学性能试验研究

通过添加不同含量的发泡聚苯乙烯(EPS)颗粒来预制目标孔隙率以模拟混凝土的不同孔洞缺陷,制备了不同孔隙率的C25和C30两种强度等级的混凝土试件,开展单调及往复荷载下含孔洞缺陷混凝土力学性能的试验研究,分析了混凝土试件破坏形态、强度、应变、弹性模量等随孔隙率的变化规律,探讨不同孔洞缺陷对混凝土力学性能的影响。试验结果表明:单调及往复荷载下,无预制孔洞缺陷的混凝土试件均表现为脆性破坏特征。但随着孔隙率的增加,混凝土试件的强度明显降低,应力-应变曲线逐渐趋于鱼肚状分布,试件由脆性向延性破坏转变,逐渐呈现多裂缝扩展特征,特别是对于往复加载情况。两种加载方式和两种强度等级条件下,试件主要力学参数随着预制孔隙率的增加均表现出一致的变化规律。峰值应力和弹性模量随孔隙率的上升呈指数下降,而峰值应变和应变极值呈线性增大。往复荷载下试件力学性能受孔隙率的影响程度均大于单调加载情况,而且,这种影响随混凝土强度的提高而减小。在往复加载过程中,孔隙率越大,峰值应力前试件的刚度比值越大,而峰后的刚度退化也愈严重。对于相同的孔隙率,混凝土强度等级越高,峰值应力前的刚度增长率及峰后的刚度退化程度越小。     

超声辅助双螺杆机制备高密度聚乙烯/超高分子量聚乙烯复合材料及性能研究

利用超声辅助双螺杆挤出机制备高密度聚乙烯（PE-HD）/超高分子量聚乙烯（PE-UHMW）复合材料，并考察PE-UHMW含量对复合材料流变性能、结晶行为及力学性能的影响。结果表明，当PE-UHMW的含量不超过2.0 %（质量分数，下同）时，PE-UHMW在PE-HD基体内均匀分散，不存在相分离；由于PE-UHMW的相对分子质量非常大，分子链非常长，缠结程度大，其分子链松驰时间较长，有利于形成结晶前驱体，直至成核，随着PE-UHMW含量的增加，有利于成核，晶核数目明显增加，同时，PE-UHMW与PE-HD的缠结程度变大，约束了PE-HD分子链的运动，使其吸附于晶核心表面，分子链折叠排列形成结晶，最终复合材料体系的结晶度逐渐增大，片晶增厚；加入PE-UHMW后，复合材料的屈服强度、拉伸强度和断裂伸长率均明显提高。