【作者】 白时兵；

【导师】 王琪；

【作者基本信息】 四川大学 ， 材料学， 2007， 博士

【摘要】 聚甲醛(POM)是一种重要的工程塑料，其高性能化是国民经济关键需求。本文创造性地制备和研究了POM/PEO晶/晶共混体系，采用聚氧化乙烯(PEO)改性POM，通过调节共混物组成、加工中的温度和应力等形成共混物中不同尺度的共混晶结构，制备高性能POM/PEO共混材料，发展聚合物晶/晶共混理论。本文研究了POM与PEO的相容性，尤其是链构象空间特性与相容性的关系。研究了POM/PEO晶/晶共混体系的结晶行为，通过调节PEO与POM的分子量、POM的种类、POM与PEO的比例、降温方式以及加工中的剪切力场等控制共混物的结晶结构，获得了具有不同尺度共混晶结构和性能的POM/PEO共混物，讨论不同尺度结晶结构与共混物性能之间的关系，提出利用不同尺度结晶结构增韧POM的新理论，制备了具有高韧性、高耐磨自润滑POM/PEO共混材料。具体结论如下：1．POM与PEO在无定形态和熔融态相容性较好，这是由于POM与PEO链构象空间特性使其分子链可包合、缠结。2．PEO含量和分子量对POM/PEO共混物结晶结构影响较大。当PEO含量较小或分子量较低时，PEO不能结晶，无定形PEO穿插在POM微纤晶间；PEO含量或分子量增大，PEO受限结晶，结晶温度较纯PEO降低了35℃，形成微纤晶与POM微纤晶互相穿插。随PEO含量或分子量提高，POM微纤晶间距增大，球晶尺寸增大；继续增大PEO的含量和分子量，PEO形成独立的球晶结构。3．PEO没有改变POM的成核方式，但抑制了POM的成核速度和晶体生长速度，使共混物中POM的结晶温度、相对结晶度以及熔融温度下降；在PEO含量较高时，共混物中PEO受POM的影响，结晶成核方式由均相三维成核转变为异相三维成核，PEO的结晶温度升高，但由于POM抑制作用使PEO相对结晶度和熔点下降。4．共混物的韧性与其结晶结构有关，无定形PEO与POM微纤晶穿插结构有利于提高其韧性，而PEO与POR微纤晶相互穿插或球晶相互独立的结构均不利于改善材料的韧性。5．PEO能改善POM的摩擦磨损性能，原因是在摩擦过程中，PEO熔融并在摩擦界面形成润滑层。随PEO含量增大，共混物的摩擦系数迅速减小。磨痕宽度则先减小后增加，这是因为随PEO含量增加，其结晶结构发生了变化，无定形PEO与POM微纤晶穿插有利于减小磨痕宽度。6．降温方式对POM/PEO的结晶结构和力学性能影响较大。降温过程中POM晶体间无定形区域的大小和PEO结晶是影响共混物结晶形态的主要因素。控制POM的结晶，调节POM晶体间的无定形区域的大小以及PEO的结晶，可分别得到无定形PEO夹杂在POM微纤晶间、PEO微纤晶和POM微纤晶相互穿插以及PEO球晶和POM球晶相互独立的结晶结构。在降温模式1中(将试样直接从熔融态淬冷至PEO的结晶温度以下，越过POM与PEO的结晶温度)，POM与PEO共混物主要形成无定形态PEO夹杂在POM微纤晶间或PEO与POM微纤晶穿插的结晶结构，材料韧性较高；降温模式2中(试样从熔融态骤冷至PEO结晶温度，越过POM结晶区，让PEO充分结晶)，不同PEO含量的共混物都形成PEO球晶与POM晶体互相独立的结晶结构，韧性较差；在降温模式3中(将试样从熔融态冷却至POM的结晶温度，使POM充分结晶，再骤冷至PEO结晶温度以下，越过PEO的结晶区)，在PEO含量为5％和10％的共混物中主要形成无定形PEO夹杂在POM微纤晶间的结晶结构，具有较高韧性，而PEO含量为50％的共混物则形成了PEO与POM球晶互相独立的结晶结构，但由于PEO已经形成互串网络结构，具有较高韧性，但拉伸强度较低；在降温模式4(先将试样从熔融态冷却至POM的结晶温度，使POM充分结晶，再降温至PEO结晶温度，让PEO充分结晶)和降温模式5(以10℃/min从熔融态降温至PEO的结晶温度以下)中，当PEO含量为5％时，共混物形成无定形PEO夹杂在POM微纤晶间的结晶结构，而PEO含量为10％的共混物形成PEO微纤晶与POM微纤晶互相穿插的结晶结构，PEO含量为50％共混物形成了PEO球晶POM球晶互相独立的结晶结构。在所有降温模式的共混物中，当PEO含量为5％，降温模式4时共混物的综合力学性能最优，原因是此时形成了无定形PEO存在于POM球晶微纤晶间的结晶结构，且POM的结晶度最大。7．POM/PEO共混体系熔体粘度对温度不敏感，但对剪切较为敏感，可以在加工中通过改变剪切速率调节POM/PEO的分散相尺寸、结晶结构和力学性能，获得具有不同结晶结构和缺口冲击强度的POM/PEO共混物。对PEO含量为5％的共混体系，随剪切速率增加，PEO分散相尺寸减小，但共混体系的结晶结构不发生变化，仍为无定形的PEO夹杂在POM微纤晶间的结晶结构，缺口冲击强度和拉伸强度变化不大；在PEO含量为10％和20％的共混物体系中，随剪切速率增加，PEO的分散相尺寸变小且共混物的结晶结构由PEO与POM球晶互相独立结构向POM与PEO微纤晶穿插的结构转化，提高了共混物的缺口冲击强度，但拉伸强度变化不大。8．PEO分散相尺寸直接影响POM/PEO共混物的结晶结构，其在1um附近可能存在一临界值，大于该临界值时，体系形成POM与PEO球晶相互独立的结晶结构，反之，则形成PEO与POM微纤晶互相穿插的结晶结构。9．当PEO分子量为50万，含量为5％(wt％)时，共混体系具有优良的综合性能，缺口冲击强度达12.8kJ/m~2，是纯POM缺口冲击强度的2倍左右，而拉伸强度下降不大，同时该体系的摩擦系数和磨痕宽度分别为0.18和3.5mm，较纯POM分别下降～50％和～35％。更多还原

【Abstract】 Polyoxymethylene (POM) is one of the important engineering plastics. Its modification is in great demand for the national economy. In this thesis, poly oxide ethylene (PEO) was adopted to modify POM, and a novel POM/PEO crystalline/crystalline system was prepared and studied. By controlling the multi-scale crystalline structure through adjusting the content and structure of the components, as well as the processing temperature and shear stress, POM/PEO blend with enhanced mechanical properties was obtained, which contributed to the present polymer crystalline/crystalline theory.In this thesis, compatibility of POM/PEO blend, particularly their compatibility induced by the space characteristic of the chain conformation of both PEO and POM molecules was discussed. POM/PEO blends with high impact strength, self-lubrication and anti-wear properties were prepared by controlling the multi-scale crystalline structure in POM/PEO blends through changing the content of components, the temperature and stress during processing, which provides a new way to modify POM with enhanced performances.The main conclusions of the research are as follows:1. Due to their special chain conformations, POM and PEO chain segments can include or tangle each other, endowing POM/PEO with pretty good compatibility at the amorphous state.2. PEO content and molecular weight have great influence on the crystalline structure in POM/PEO blends. PEO with low content or small molecular weight does not crystallize due to the restriction of the confined environment, only exists as amorphous state in the space among POM lamellae, thus enlarging the spherulite size of POM. When increasing PEO content or molecular weight, although the confined environment is extended and PEO can crystallize, the crystallization of PEO is still retrained and crystallization temperature decreases to 5℃, 35℃lower than the crystallization temperature of neat PEO, forming POM/PEO interfibrillar segregation. With further increase of PEO content or molecular weight, PEO crystallizes independently, forming POM/PEO interspherilute segregation.3. In POM/PEO blends, PEO doesn’t change the nucleating way of POM but restrains its nucleating rate and crystal growing, resulting in that the crystallization temperature, melting point and relative crystallinity of POM decrease. However, the nucleating way of PEO in the blends changes. POM crystal acts as nucleating agent for PEO, inducing that the crystallization temperature of PEO increases, and melting point and relative crystallinity of PEO decrease.4. The toughness of POM/PEO blend depends on the crystalline structure of the blend. The materials with the crystalline structure that amorphous PEO exists among POM lamellae have the best toughness. However, POM/PEO interfibrillar segregation and the interspherilute segregation crystalline structures seem unfavourable for the toughness of the blends.5. PEO can improve the friction and wear properties of POM/PEO blends because PEO in the blend melts during friction and transfers to the friction surface, forming a lubricative layer. With PEO content increasing, the friction coefficient decreases greatly. The materials with the crystalline structure that amorphous PEO exists among POM lamellae have a less abrasion.6. The way of temperature decreasing in sample preparation has great influence on the crystalline structures and therefore mechanical properties of POM/PEO blends. The size of POM amorphous region and the crystallization of PEO in the process of temperature decrease are the main factors determining the multi-scale crystalline structures in POM/PEO blends: amorphous PEO among POM lamellae, POM/PEO interfibrillar segregation crystalline structure or POM/PEO interspherilute segregation crystalline structure. By model 1 (directly quenching samples from the melt to the temperature below PEO crystallization point), amorphous PEO exiting among POM lamellae or POM/PEO interfibrillar segregation are formed, and the material has pretty good toughness.By model 2 (quenching samples from the melt to PEO crystallization temperature, getting across POM crystallization temperature and allowing PEO to well crystallize), POM/PEO interspherilute segregation crystalline structure in all blends is formed, and the toughness of the materials become worse.By model 3 (decreasing temperature from the melt to POM crystallization temperature and allowing POM to well crystallize, then quenching to the temperature below PEO crystallization point ), When PEO contents are 5% and 10%, interfibrillar segregation crystalline structure is formed, and the blends have higher notched impact strength. But when PEO content is 50%, the crystalline structure of the blend is interspherilute segregation. The blend has better toughness due to the formation of internet phase morphology, but the tensile decreases greatly.By model 4 (letting both PEO and POM well crystallize) and model 5 (decreasing temperature at a rate of 10°C/min), when PEO content is 5%, the blend forms amorphous PEO existing among POM lamellae. When PEO content is 10%, the blend forms interfibrillar segregation crystalline structure. However, when PEO content is 50%, the blend forms interspherilute segregation crystalline structure.In all the decreasing temperature models, when PEO content is 5%, the material prepared by models 4 has the best comprehensive mechanical properties because the crystalline structure of amorphous PEO existing among POM lamellae is formed, and POM also has the highest crystallinity.7. The melt viscosity of POM/PEO blend is sensitive to shear rate. The crystalline structure of POM/PEO blend can be controlled by adjusting the injection speed and the size of dispersing phase in injection process. When PEO content is 5%, with the shear rate increasing, although the dispersing phase of PEO becomes smaller, the crystalline structure that amorphous PEO exists among POM lamellae doesn’t change. When PEO content is 10% and 20%, with the shear rate increasing, the crystalline structure of POM/PEO blend changes from interspherilute segregation to interfibrillar segregation, resulting in an increase of notched impact strength.8. The size of PEO dispersing phase affects the crystalline structure in POM/PEO blend. There may be a critical value of PEO dispersing phase size around 1μm, lager than which forming POM/PEO interspherilute segregation crystalline structure, smaller than which forming POM/PEO interfibrillar segregation crystalline structure.9. When PEO content is 5% and molecular weight is 5.0×10~5, the blend has pretty good comprehensive mechanical properties. The notched impact strength can reach 12.9 kJ/m~2, double that of POM, and the wear scar width and the friction coefficient are 0.18 and 3.5mm respectively, only about 50% and 35% of that of POM.更多还原