【作者】 刘功德；

【导师】 李惠林；

【作者基本信息】 四川大学 ， 材料学， 2003， 博士

【摘要】 采用加工助剂与超声辐照相结合的方法，实现了超高分子量聚乙烯(UHMWPE)在一般单螺杆挤出机上的挤出加工，提出了流动改性机理；研究了挤出过程中超声辐照对UHMWPE的加工流变性及结构与性能的影响，实现了采用超声辐照技术解决链缠结密度高聚合物的难加工和高性能化难点；研究了UHMWPE的摩擦磨损性能，得到具有优良耐磨性能特别是抗疲劳磨损性能的UHMWPE，提出了改善UHMWPE摩擦磨损性能的机理。 1．采用加工助剂与超声辐照相结合的方法，实现了UHMWPE在一般单螺杆挤出机上的连续挤出成型。加入一定量的聚丙烯(PP)，能有效改善单螺杆挤出机对UHMWPE的加工性能，挤出过程中的超声辐照则有效地降低了熔体粘度和挤出压力，显著提高了挤出效率。在适当的加工助剂含量和超声辐照强度下，UHMWPE的力学强度、耐热性能及摩擦磨损性能得到提高。 2．研究了UHMWPE在挤出过程中物料输送及熔融塑化机理。FT-IR、DSC、WAXD和AFM分析表明，在单螺杆挤出机挤出UHMWPE/PP共混物时，与料筒壁接触的物料表层主要是PP，从而增大了物料一料筒壁间的摩擦系数，实现了单螺杆挤出机内物料的顺利输送。在熔融塑化过程中，PP首先熔融并在料筒壁形成熔膜，熔膜流入主动螺腹形成熔体池，对被动螺腹中的UHMWPE固体床产生大的推压力，使UHMWPE固体床得以压实，解决了通常用一般单螺杆挤出机挤出UHMWPE时的打滑、料塞和不能压实的问题。在以聚乙烯(PE)改进UHMWPE加工流动性的情况下，熔融的PE很快渗入到UHMWPE内部，不能有效地在料筒壁一物料间聚集，也不能形成有效的熔体池，加之UHMWPE低的摩擦系数和不粘性，在用单螺杆挤出机挤出UHMWPE时就遇到困难。微观结构分析表明，在UHMWPE/PP共混物中，PP位于UHMWPE晶区间的低晶(非晶)区域，破坏了UHMWPE完整的链缠结网络，有效地降低了UHMWPE链缠结密度，流动性得以改善。PE不能有效降低UHMWPE的链缠结密度，因而PE对UHMWPE加工改性效果较差。 3．挤出过程中的超声辐照显著降低了UHMWPE/PP共混物熔体表观粘 摘要度和挤出口模压力，提高了挤出产量。随共混物中PP含量的减少，共混物熔体的链缠结密度升高，超声辐照的降粘降压效果越明显。超声辐照使共混物中UHMWPE和PP的结晶度下降，晶粒尺寸变小。在适当的超声辐照强度下，材料的抗冲击强度、杨氏模量及耐磨性能得到提高。 4.以PP为主的加工改性剂能显著提高UHMWPE的摩擦磨损性能。在同样的条件下，UHMWPE的摩擦系数和磨损速率都比UHMWPE/PP共混物高。随负荷的增加和磨损时间的延长，在UHMWPE磨损表面出现大量的裂纹，呈现明显的疲劳磨损特征。在较高的滑动速度下(400rpm)，UHMWPE发生因表面熔融而导致快速的磨损。而UHMWPE/PP共混物在高的负荷、长的磨损时间及高的滑动速度下，在磨损表面无明显的疲劳破坏和熔融现象发生。通过原子力显微镜(AFM)观察研究表明，在不同的作用力范围和滑行速度下，UHMWPE的表面层分子与 Si3N4探针间的摩擦力均较UHMWPE用P共混物高，与宏观的摩擦性能相一致。 5.采用SEM、FT一IR、DSC、AFM、XPS和场伙XD研究了UHMWPE和uHMwPE/PP的摩擦磨损机理。与uHMwPE对磨时，在钢环表面形成了UHMWPE转移膜，与UHMWPE/PP对磨的钢环表面无转移膜，而有很细的圆柱状磨屑产生。长的磨损时间导致UHMWPE疲劳破坏，产生大量的磨屑，而随磨损时间的延长， UHMWPE/PP表面的磨屑并无明显的增加。由于钢环滑动对表面层分子所产生的剪切、拉伸及退火作用，在UHMWPE/PP的磨损表面形成了串晶，而UHMWPE磨损表面的晶区较小，晶区间的粘接力也较弱。UHMWPE/PP共混物在磨损初期所产生的少量圆柱状磨屑分布于摩擦界面，起到了有效地将滑动摩擦转化为滚动摩擦的作用，因而摩擦系数和磨损速率显著降低，耐磨性能明显提高。更多还原

【Abstract】 Processing aid agents and ultrasonic wave were introduced during processing of ultrahigh molecular weight polyethylene (UHMWPE) with a general single-screw extruder. The mechanism of the conveying, melting, plasticating in the extruder and the effect of ultrasonic wave at the die during extrusion were studied. The mechanical and anti-wear properties of the extrudate, and the mechanism of the anti-wear enhancing owing to the addition of PP were explored. The experimental results show that.1.The addition of polypropylene (PP) improves the processability of UHMWPE, ultrasonic wave at the die during extrusion can effectively reduce the melt viscosity and die pressure, the extrusion efficiency is thus improved. Appropriate amount of PP and ultrasonic wave intensity can improve the mechanical strength, heat-distortion temperature and the anti-wear properties of UHMWPE.2. The mechanism of conveying, melting and plasticating of UHMWPE in the extruder were investigated with screw extraction experiment. FT-IR, DSC, WAXD and AFM show that PP is enriched between the blend and the barrel wall, thus increases the frictional force on the wall, the conveying of the solid down to the channel could be carried out. FT-IR, SEM analysis reveals that during the melting and plasticating of UHMWPE/PP blend in the barrel, PP melted first, melt film was formed on the barrel wall. The melt flows from the melt-film toward the active flight flank to form melt pool, exerting considerable pressure on the UHMWPE powder in the passive flight flanks, the hard-compacted problem ofABSTRACTUHMWPE is thus overcome. In the case of UHMWPE/PE blend, the melted PE penetrates into UHMWPE domains immediately, there is not enough PE melt aggregated on the barrel wall and PE melt pool could not be formed in the active flight flanks, therefore the UHMWPE powder in the passive flight flanks could not get enough pressure to have them compacted, combined with the low friction coefficient and the nonsticeness of UHMWPE to the barrel wall, the extrusion of UHMWPE with general single screw extruder is rather difficult. Microstructure analysis shows that PP located in the amorphous zone (or low crystallimty zone) among UHMWPE crystal domains, the net of UHMWPE chain entanglement is destroyed, the chain entanglement density of UHMWPE is decreased effectively, the flowability of UHMWPE is increased prominently upon the addition of PP. PE could not reduce effectively the chain entanglement density of UHMWPE, the enhancement of processability of UHMWPE by the addition of PE is rather limited.3. Ultrasonic wave at the die during extrusion can reduce the die pressure and the apparent viscosity of UHMWPE/PP blend prominently. Ultrasonic effects also contribute to the increase of output. The effect of ultrasonic wave on the reduction of the apparent viscosity is extremely remarkable to UHMWPE/PP blend. With the decrease of PP content in the UHMWPE/PP blend, the chain entanglement density increased, the effectiveness of the melt viscosity and die pressure reduction increased. The higher the entanglement density, the more the apparent viscosity was reduced. Ultrasonic wave can reduce crystal dimension and crystallinity. With appropriate dose of ultrasonic treatment, the impact strength, young’s modulus and anti-wear properties of the extrudate are improved.4. The anti-wear property of UHMWPE can be improved by blending it with appropriate amount of PP. The friction coefficient and wear rate of UHMWPE are much higher than those of UHMWPE/PP blend, the wear rate of UHMWPE is more sensitive to load and wear time than that of the UHMWPE/PP blend. Long scratch grooves and cracks occurred in the worn surface of UHMWPE, while no such serious damage is observed in the worn surface of the UHMWPE/PP blend.IVUnder high sliding speed(400rpm), the temperature of the worn surface is so high, the melt loss is the major cause of UHMWPE wearing, no melting trace could be detected in the worn surface of UHMWPE/PP blend. AFM indicates that friction force between UHM更多还原