【作者】 蒋舒；

【导师】 杨鸣波；

【作者基本信息】 四川大学 ， 材料加工工程， 2007， 硕士

【摘要】 聚丙烯(PP)一直是有机高分子合成材料最重要的产品，但PP的氧指数低，容易燃烧，且燃烧速率快，发热量高，并伴有熔滴现象，容易引起火灾，限制了其在实际中的广泛应用。尽管对填充型阻燃剂改性PP已经有不少研究，并取得了很大进展。但是绝大部分阻燃剂的加入都会破坏PP的力学性能。本研究工作针对以上问题，采用新型阻燃剂可膨胀石墨，考察了其对PP阻燃性能，力学性能和熔融结晶等方面的影响，将主要结论归结为以下几点：可膨胀石墨是一种经硫酸和硝酸插层后的石墨，和普通石墨有类似的晶体结构。每一层中，EG靠碳原子的共价键作用。层与层之间靠范德华力作用。膨胀后的EG粒子有许多空隙，该空隙是由于石墨碳层间被高温膨胀爆破所致。经过高混机混合后，由于机械力的作用，石墨粒子的平均粒径和平均面积都有明显减小，层数也变为得很小，甚至单层。压制成型的EG／PP复合材料阻燃性能优于注射成型。分析其机理，由于燃烧后的膨胀石墨粒子作为燃烧样品的物理阻隔层，隔绝氧气和燃烧的样品基体，从而达到阻燃的目的。压制成型试样在加工过程中所受剪切作用较小，石墨的层状结构保留较完整，所以有足够的膨胀倍率，能较多的覆盖样品的表面，从而达到阻燃的目的；而对于注射成型试样而言，由于加工过程中所受剪切作用较大，石墨的层状结构保留很不完整，所以膨胀倍率较小，燃烧后产生的膨胀石墨粒子较小，不足以覆盖样品表面，最终导致PP的阻燃性能较差。EG／PP复合材料的冲击性能随着EG含量的增加先升高后降低。在5％时出现最大值。体系的拉伸强度也随着EG含量的增加而缓慢降低。体系的模量随EG的含量增加呈上升趋势。将EG／PP试样退火后，体系的冲击性能有较大提高，并且随着EG含量的增加，同样有一个先升高后降低的过程。加入EG粒子以后，PP晶片厚度变化不大，但更均匀，结晶的均匀性略有提高。EG粒子还有成核剂的作用，使PP从均相成核过程转变为异相成核过程，结晶时间大大缩短，形成的α球晶尺寸大大降低。退火后，PP和PP／EG体系的晶体结构都有一定程度的完善，晶片厚度有一定的增加，熔点升高。在EG／PP体系芯层，发现了少量的β晶。可以认为在注射过程中，EG的存在诱导了β晶的生成。但由于β晶的生成还和过冷度密切相关，因此在示差扫描量热仪(DSC)中退火后，β晶消失了。EG／PP体系在退火后冲击强度大幅上升，并非β晶增加造成，可能是退火消除了试样内应力，使体系的晶体结构更加完善所至。更多还原

【Abstract】 Polypropylene (PP) is always the most important products of polymer materials, but the low limiting oxygen index, high burning rate, high quantity of heat release, and easy causing of fire, which limit the application range. Although many researches have been done on flame retardants filled PP, but introducing of retardants greatly affects the mechanical property of PP. In this paper, a new kind of polymer composites is obtained by adding a new kind of retardant-Expandable Graphite (EG). Combustion performance, mechanical property, melting and crystallization has been studied. The main conclusions were listed as followings.EG which intercalated by sulfur acid and nitrate acid has a similar crystal structure with graphite. The main force between the carbon atoms is covalent bond in each layer while between the layers is van der waals force. There are many voids between layers in EG after expansion. After treated in high speed mixer, mechanical force makes the average diameter and average area of EG become small and layers decrease.EG/PP composites made by compression has a better combustion performance than by injection molding. The reason summaries as follows: As a flame retardant, EG after combustion acts as a physical obstruct on the surface of the matrix and separated oxygen and PP. It is found that the composites are strongly affected by the integrity of the structure of EG which can be easily damaged by shear stress. Compare to the injection molding, there is less shear force in compression processing. So combustion property of compression molded EG/PP composites is better.With increase of EG, Izod impact strength of PP/EG composites first increase, then decrease and reaches a maxim when the content of filler is 5 percent. Tensile strength decreases while Yang’s modulus increases. Annealed sample presents a great increase of impact strength.Lamellar thickness and uniformity improves when adding EG into PP. As a nucleate agent, EG has many positive effect; it makes PP from homogenous nucleation to heterogeneous nucleation, it shorten the crystal time and size of a crystal. After annealing, PP and PP/EG composites have a better crystal structure.βcrystal is induced by EG and found in core section of impact bars.βcrystal disappeared when annealing in Differential Scanning Calorimeter(DSC) due to high degree of supercooling. The great increase of impact strength after annealing is not caused by increase of quantity ofβcrystal, may be due to elimination of innerstress and improve of crystal structure.更多还原