丙烯酸十八酯共聚物的结晶和熔融行为研究

合成了丙烯酸酯(AAn,n为侧链碳原子数)均聚物(PAAn)以及AA18与其同系物的无规共聚物((P(AA18-co-AAn)),并研究了P(AA18-co-AAn)的结晶和熔融行为.结果表明,在AA18与结晶同系物AAn(n=10,12,14,16)的共聚物中,结晶度(Xc)随AA18含量的增加而增大,相应的熔程先增加后下降,存在一个最大值;P(AA18-co-AA14)和P(AA18-co-AA16)的相对结晶度(Xc/Xcmax)受AA18含量影响不大,而P(AA18-co-AA10)和P(AA18-co-AA12)的Xc/Xcmax随AA18含量增加先下降后上升;随着AA18与共聚组份侧链碳原子数差别的增大,熔程的最大值明显增加.在AA18与非结晶同系物AAn(n=4,6,8)的共聚物中,Xc和Xc/Xcmax值随AA18含量的增加而增大,而Xc/Xcmax值随AAn侧链碳原子数的增加而减少,共聚物熔程的最大值差别不大.     

等规聚丙烯在γ射线辐照下的链结构和结晶行为

利用凝胶渗透色谱(GPC)、傅里叶变换红外光谱(FTIR)和示差扫描量热(DSC)等手段对不同剂量γ射线辐照后等规聚丙烯(iPP)的分子链结构及结晶行为的变化进行了研究.结果表明,γ射线辐照使iPP的分子量下降,并在其分子链中产生羟基和羰基等极性基团,从而影响其结晶行为.在非等温结晶过程中,当辐照剂量≤50 kGy时,iPP的热结晶温度略有升高;增大辐照剂量,iPP的热结晶温度明显降低.iPP的熔融温度则随辐照剂量的增大而降低,且分裂成双峰.利用Avrami方程研究了辐照前后iPP的等温结晶动力学,发现辐照前后样品的Avrami指数n都在3左右,表明iPP的结晶遵循异相成核机理,且不受辐照剂量和等温结晶温度的影响,但总结晶速率随等温结晶温度和辐照剂量的升高而逐渐减小.探讨了iPP经过γ射线辐照后,分子链断裂、链结构变化和结晶速率之间的关系.     

原位聚合聚乙烯/蒙脱土纳米复合材料的结晶行为

用DSC研究了HDPE与MMT负载的催化剂熔融共混和原位聚合得到的两种纳米复合材料的熔融、 结晶行为和等温结晶动力学.  结果表明, HDPE与熔融共混样品的结晶度、 平衡熔点、 球晶生长速率和结晶能力大体相同; 原位聚合得到的HDPE/MMT纳米复合材料的结晶度和平衡熔点高于纯HDPE; 在相同过冷度条件下熔融结晶速率和结晶能力低于纯HDPE, 而在相同结晶温度Tc下, 熔融结晶速率和结晶能力则高于纯HDPE.  纯HDPE的晶体生长侧向单位面积表面自由能最小, 其次是熔融共混样品, 原位聚合样品最大, 且随ＭＭＴ含量的增加逐渐升高.     

聚丙烯／聚乙烯共混物高取向薄膜的形态结构研究

在等规聚丙烯(iPP)与高密度聚乙烯(HDPE)共混物的熔体拉伸薄膜中,两组份均以高取向的片晶形式存在,片晶生长方向垂直于拉伸方向。当iPP含量小于20％时,无明显的iPP相区存在;在iPP含量为40—60％时,两组份各自形成继续相,而在iPP含量大于70％时,HDPE以分散相存在。iPP的加入,使HDPE的片晶宽度减小,同时影响其结构的对称性,即由纯HDPE的非对称近单晶结构变为对称的纤维结构。 在制膜温度较高(135—140℃),HDPE含量较低(小于30％)时,HDPE在iPP上附生结晶。两种片晶的c轴成45°—50°交角,附生结晶的接触面为HDPE的(100)和iPP的(010)。     

高密度聚乙烯与EPDM磺酸锌盐共混物结构与性能的研究

本文研究了高密度聚乙烯(HDPE)/EPDM磺酸锌盐(Zn-SEPDM)共混物的机械性能、流变行为、形态和相容性。结果表明:加入Zn-SEPDM可使HDPE的熔点和结晶度降低,熔程变窄。当Zn-SEPDM含量超过20％,共混物中Zn-SEPDM呈连续相,冲击强度突增。     

交联聚乙烯的结晶行为研究

本论文采用熔融共混法制备了高密度聚乙烯(HDPE)/光引发剂(BDK)/交联剂 (TAIC) 共混物,再用高压汞灯辐照制备一系列不同交联程度的样品。通过广角X射线衍射(XRD)与差示扫描量热法(DSC)等手段研究了紫外光交联对HDPE的晶体结构及非等温结晶动力学行为的影响。研究结果表明：紫外光交联不改变HDPE晶型;随着光交联时间的增加,结晶峰的强度下降;晶粒尺寸变小。随着降温速率的增加,HDPE与交联HDPE (XLPE)的结晶峰变宽,结晶温度(Tp)向低温方向移动,结晶速率变快,结晶度(Xc)下降。相比较而言,XLPE的Tp较低,F(T)较大,Xc较小,结晶活化能(?E)较高,表明紫外光交联抑制了HDPE的结晶。     

紫外光交联聚乙烯的结晶行为

采用熔融共混法制备了高密度聚乙烯(HDPE)/光引发剂(BDK)/交联剂 (TAIC) 共混物,在高压汞灯辐照下制备了一系列不同交联程度的样品. 通过广角X射线衍射(XRD)与差示扫描量热法(DSC)等测试技术研究了紫外光交联对HDPE的晶体结构及非等温结晶动力学行为的影响. 结果表明,紫外光交联不改变HDPE晶型. 随着光交联时间的增加,结晶峰的强度下降,晶粒尺寸变小. 随着降温速率的增加,HDPE与交联HDPE(XLPE)的结晶峰变宽,结晶温度(Tp)向低温方向移动,结晶速率变快,结晶度(Xc)下降. 相比较而言,XLPE的Tp较低,F(T)较大,Xc较小,结晶活化能(ΔE)较高,表明紫外光交联抑制了HDPE的结晶.     

流变-导电同步测试法研究炭黑填充高密度聚乙烯的等温结晶行为

采用流变-导电同步测试法,研究炭黑(CB)填充高密度聚乙烯(HDPE)在124.3～125.3℃范围的等温结晶行为,发现应变、频率与预降温速率均显著影响等温结晶过程中动态流变与导电行为.动态储能模量(G')与电阻均在结晶过程中发生显著变化.其中,CB粒子在熔体中发生扩散,造成原有逾渗网络结构破坏,导致复合体系电阻在结晶诱导期内增大.随结晶度增加,G'在结晶诱导期附近开始显著增大,其临界时间对应1%～2%相对结晶度;同时,CB粒子在无定形区相互聚集而形成渗流网络结构,使得复合体系电阻显著降低.电阻的变化被认为与CB粒子在熔体中的迁移以及在HDPE晶体生长过程中的聚集行为有关,且比依时性动态流变行为更敏感.     

苯乙烯-氧乙烯-苯乙烯三嵌段聚合物的受限结晶行为的反气相分析

 采用反气相法研究了苯乙烯 氧乙烯 苯乙烯三嵌段结晶聚合物 (PS PEO PS)的结晶熔融相变 ,测定了PS PEO PS的结晶度、熔点以及熔程 ,探讨了正构烷烃探针分子的碳链长度对测定结果的影响。研究结果表明 :PS PEO PS的微相分离对PEO链段的结晶行为有较大的影响 ,其晶体结构中存在由多种不完善PEO结晶和PS非结晶构成的中间层 ;正构烷烃探针分子的碳链长度对测定PS PEO PS的熔点和熔程无影响 ,但对结晶度测定和PEO结晶熔融相变的检测影响较大 ,所测得PS PEO PS的结晶度随正构烷烃探针分子碳链的增长而降低。     

等规聚丙烯在混合稀释剂中结晶行为

利用偏光显微镜和扫描电子显微镜研究了等规聚丙烯(iPP)在混合稀释剂中的非等温结晶行为和由热致相分离(TIPS)法制备的iPP微孔材料的结构。iPP的质量分数固定为30%,采用不同配比的邻苯二甲酸二丁酯(DBP)/大豆油组成混合稀释剂。结果表明,混合稀释剂的配比影响体系的粘度和稀释剂与iPP的相容性,进而影响iPP球晶的生长和TIPS法制备的iPP微孔材料结构。在2K/min的降温速率的条件下,iPP球晶半径和球晶的生长速率均随时间的延长呈指数增长,iPP球晶生长速率随混合稀释剂中DBP含量的增加而降低,当iPP球晶生长时间达2min时,混合稀释剂中DBP的质量分数从0增加到60%,iPP球晶生长速率从41.9μm/min降至10.3μm/min,所制得的微孔材料断面均呈蜂窝状结构,且孔径随混合稀释剂中DBP含量的增加有明显增大的趋势。     

Thermal,rheological, morphological and mechanical properties of high density polyethylene/ethylene vinyl acetate copolymer (HDPE/EVA) blends

Thermal, rheological, morphological and mechanical properties of binary HDPE and EVA blends were studied. The results of rheological studies showed that for given HDPE and EVA, the interfacial interaction in HDPE-rich blends is higher than EVA-rich blends. Using three different rheological criterions, the phase inversion composition was predicted to be in 30 wt% of the EVA phase. This showed good agreement with morphological studies. The tensile strength for HDPE-rich blends showed positive deviation from mixing rule, whereas the EVA-rich blends played negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The thermal analysis revealed that high co-crystallizaiton in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. Furthermore, the results of thermal behavior of the blends indicated that the melting temperatures of HDPE decrease due to the dilution effect of EVA on HDPE.     

Phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene/high density polyethylene blends

The phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends were investigated. It was found that the properties are intimately related to each other. The morphology of the blends showed a two phase structure in which the minor phase was dispersed as domains in the major continuous matrix phase. The domain size of the dispersed phase increased with increasing concentration of that phase due to coalescence. It was also found that the domain size of the dispersed phase depends on the viscosity difference between the two phases. For a given HDPE/iPP blend, where HDPE is the matrix and iPP is the dispersed phase, the iPP domains were smaller than HDPE domains of the corresponding iPP/HDPE blend where iPP is the matrix and HDPE is the dispersed phase. A co-continuous morphology was observed at 50/50 PP/HDPE composition. Crystallinity studies revealed that blending has not much effect on the crystalline melting point of polypropylene and high density polyethylene. The crystallisation enthalpy and heat of fusion values of HDPE and PP in the blend were decreased as the amount of the other component increased. The variation in percent crystallinity of HDPE and PP in the blend was found to depend on the morphology of the blend. All the mechanical properties except Young's modulus and hardness showed negative deviation from the additivity line. This is due to the incompatibility of these blends.     

Morphology evolution of polypropylene in immiscible polymer blends for fabrication of nanofibers

Immiscible blends of cellulose acetate butyrate (CAB) and isotactic polypropylenes (iPPs) with different melting index were extruded through a two‐strand rod die. The extrudates were hot‐drawn at the die exit at different draw ratios by controlling the drawing speed. The morphologies of iPP fibers extracted from the as‐obtained extrudates after removal of CAB by acetone were investigated by scanning electron microscopy. The influences of draw ratio, viscosity ratio, and composition ratio of CAB/iPP on the morphology evolution of iPP phase into nanofibers in the immiscible blends were studied. It was found that the thermoplastic iPP nanofibers were formed from the elongation of iPP ellipsoids, end‐to‐end merging of elongated iPP microfibers, and the size decrease of iPP microfibers in the processes of extrusion and drawing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 921–931, 2010     

Dynamic mechanical investigations on drawn samples of isotactic polypropylene/EPM–Rubber blend

The physical behavior of isotropic and oriented samples of an isotactic polypropylene (iPP)/ethylene–propylene–copolymer (EPM) reactor blend was studied by performance of dynamic mechanical measurements over a wide temperature range (DMTA). The influence of thermal history and drawing procedure was examined. The results showed that with increasing draw ratio the uniaxial elastic modulus of the material was considerably enhanced, whereas the intensity and strength of the amorphous relaxations of both components were reduced. At a certain draw ratio, the glass transtions of iPP and EPM phenomenologically merged and appeared as a single relaxation. The crystalline relaxation of iPP emerged with increased draw ratio at higher temperatures and was better seperated and easier to detect. The effects observed were attributed to the orientation of the crystallites in a fibrillar structure and to the restricted molecular mobility in amorphous regions. Measurements by differential scanning calorimetry (DSC) and x-ray diffraction of several drawn samples were performed to determine the effects of drawing on the melting behavior and the crystal orientation in the semicrystalline polymer. For comparison, some results of analogous studies on neat isotactic PP are presented and discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1439–1448, 1997     

Physical and mechanical properties of ultra-oriented high-density polyethylene fibers

Ultra-oriented high-density polyethylene fibers (HDPE) have been prepared by solid-state extrusion over 60–140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x-ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20–30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two-phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x-ray measurements. Solid-state extrusion of HDPE near the ambient melting point produced a c-axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c-axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.     

Morphology and properties of isotactic polypropylene/poly(ethylene terephthalate) in situ microfibrillar reinforced blends: Influence of viscosity ratio

In situ microfibrillar reinforced blends based on blends of isotactic polypropylene (iPP) and poly(ethylene terephthalate) (PET) were successfully prepared by a “slit extrusion-hot stretching-quenching” process. Four types of iPP with different apparent viscosity were utilized to investigate the effect of viscosity ratio on the morphology and mechanical properties of PET/iPP microfibrillar blend. The morphological observation shows that the viscosity ratio is closely associated to the size of dispersed phase droplets in the original blends, and accordingly greatly affects the microfibrillation of PET. Lower viscosity ratio is favorable to formation of smaller and more uniform dispersed phase particles, thus leading to finer microfibrils with narrower diameter distribution. Addition of a compatibilizer, poly propylene-grafted-glycidyl methacrylate (PP-g-GMA), can increase the viscosity ratio and decrease the interfacial tension between PET and iPP, which tends to decrease the size of PET phase in the unstretched blends. After stretched, the aspect ratio of PET microfibrils in the compatibilized blends is considerably reduced compared to the uncompatibilized ones. The lower viscosity ratio brought out higher mechanical properties of the microfibrillar blends. Compared to the uncompatibilized microfibrillar blends, the tensile, flexural strength and impact toughness of the compatibilized ones are all improved.     

Effects of polylactic acid and rPET minor components on phase evolution,tensile and thermal properties of polyethylene‐based composite fibers

High mechanical performance and partially biodegradable PE‐composite fibers modified with polylactic acid (PLA) and recycled polyethylene terephthalate (rPET) minor components were prepared using melt extrusion and hot drawing process. Rheological properties, morphology, tensile, and thermal properties were investigated. All blends exhibited shear thinning behavior except for starting PLA and rPET. PLA and rPET dispersed phases appeared as droplets in as‐extruded strand, and PLA droplets were mostly larger than those of rPET. The fibrillation of both PLA and rPET domains was achieved after further hot drawing as the fiber. The morphology and tensile properties of the fibers mainly depended on the types and contents of dispersed phases including draw ratios. The ultimate strength of the polymer fibers at draw ratio of 20 was more than 600 times higher than that of the as‐spun sample of the same composition. Remarkable improvement in secant modulus and ultimate strength was found for PE‐30PLA, but the drawing process of this composition encountered some difficulties and rough surface of the fiber was observed. The stiffness and tensile stress for PE‐10PLA‐10rPET fiber were clearly improved when compared with PE and PE‐10PLA. A decrease in thermal stability of PE/PLA composites was observed with increasing PLA content whereas additional presence of rPET significantly increased the stability of the composites both in nitrogen and in air. PE/PLA/rPET fiber possessing high stiffness with good thermal stability prepared in this work has high potential for being utilized as structural parts for load‐bearing applications.     

Spinnability of Nanofilled Polypropylene

Summary: Spinnability of isotactic polypropylene iPP (melt flow 25 g/10 min) was studied after addition of three nanofillers at 0.3% by wt., two nanoclays and a modified hydrotalcite. TGA evidenced the increase of thermooxidation stability in nanofilled iPPs. All these iPP were successfully processed and tensile properties similar to those of iPP fibers were achieved. Processing and mechanical draw ratio were evaluated. Moreover, nanofilled iPP fibers appeared to be more prone to further drawing, as derived from both the maximum attainable strength and the maximum attainable drawing, as presented in the interpretation model of mechanical testing.     

Thermoplastic elastomer based on high‐density polyethylene/natural rubber blends: rheological,thermal, and morphological properties

Thermoplastic elastomer (TPE) comprising air‐dried sheet or natural rubber (ADS or NR) and high‐density polyethylene (HDPE) was prepared by a simple blending technique. NR and HDPE were mixed with each type of phenolic compatibilizer (HRJ‐10518 or SP‐1045) or liquid natural rubber (LNR) at 180°C in an internal mixer. The mixing torque, shear stress, and shear viscosity of the blends increased with increasing amounts of NR. Positive deviation blend (PDB) for the blends containing active hydroxyl methyl phenolic resin in HRJ‐10518 or dimethyl phenolic resin in SP‐1045 was obtained. PDB was not observed for the blends without the compatibilizers or with LNR. The blends with HRJ‐10518 or SP‐1045 were compatible or partially compatible while the LNR blends were incompatible. In the phenolic compatibilized blends, NR dispersed in the HDPE matrix was found in the NR/HDPE blends of 20/80, 40/60, and 50/50 ratios. HDPE dispersed in NR matrix was obtained in the NR/HDPE blend of 80/20 ratio, and the co‐continuous phase was accomplished in the NR/HDPE blend of 60/40 ratio. The NR/HDPE blend at 60/40 ratio compatibilized with HRJ‐10518 and fabricated by a simple plastic injection molding machine exhibited higher ultimate tensile strength and elongation at break (EB). Incorporation of parafinic oil caused a decreasing tendency in tensile strength with increases in EB. The TPNRs exhibited high elastomeric nature with low‐tension set. Copyright © 2007 John Wiley & Sons, Ltd.     

结晶聚合物品相相容性的研究

通过ＤＳＣ、Ｘ－射线衍射、红外光谱及拉伸试验研究了ＨＤＰＥ与ＬＬＤＰＥ、ＨＤＰＥ与ＬＤＰＥ之间的晶相相容性．结果表明，链结构相近的ＨＤＰＥ和ＬＬＤＰＥ的晶相相容性好，能形成共晶；而链结构差异较大的ＨＤＰＥ和ＬＤＰＥ的晶相相容性较差，倾向于分别结晶，但有部分链段被对方的晶区夹持．不论是支化度大的ＬＤＰＥ链段插入以ＨＤＰＥ为主的晶区，还是支化度小的ＨＤＰＥ链段插入以ＬＤＰＥ为主的晶区，都可破坏晶区的规整性．共晶的形成使共混物的熔点、结晶度、晶粒体积等低于两组份的线性加和，而力学性能，尤其是断裂伸长率，则显著提高，呈协同效应．