HDPE微注射成型过程非等温动态结晶模拟

采用布拉本德实验仪模拟微注射成型过程，研究结晶型聚合物微注射成型过程的剪切诱导结晶。结果表明，其他工艺参数不变时，当班伯里转子转速从40r／min增加到80r／min，试样的结晶度从74．43％增大到84．36％，结晶度随着剪切速率的增加而增大，剪切速率促进剪切诱导结晶的形成；当熔体初始温度从145℃升至185℃时，试样结晶度从74．96%增大到79．43％，结晶度随着熔体初始温度的上升而增大；当剪切时间从10min增加到20min时，试样结晶度从77．48％增大到80．17％，结晶度随着剪切时间的增加而增大，剪切作用可以促进结晶。比较动态与静态DSC的实验结果，动态结晶度（79．43％）高于静态结晶度（77．48％）。在同样的热历史影响下，剪切等外力场作用会促进HDPE的结晶过程。将上述结晶过程的研究结果应用于微注射成型生产实际，可从结晶度的角度来优化微注射成型熔体温度、注射压力和注射速率等工艺参数，提高成型零件的质量。     

天然橡胶硫化胶拉伸结晶度的测定

根据Ｘ射线衍射理论，用Ｒｕｌａｎｄ法和分峰法相结合的方法，测定了天然橡胶硫化胶拉伸不同倍数时的结晶度。此法不但计算简单，而且克服了采用单一分峰法时结晶度偏高的缺点，提高了结晶度计算的可信程度。     

振动注射实现聚丙烯试样自增强自增韧形态研究

利用自行研制的振动注射实验装置，实现振动注射成型和常规注射成型。和常规注射成型相比，随着振动频率的增加，振动注射成型的聚丙烯哑铃试样拉伸强度增加的同时，韧性也得到了一定程度的提高。SEM显示振动注射实现芯层晶粒的细化，剪切层球晶取向程度明显；DSC测试表明振动注射成型有利于试样结晶度的提高，结晶度由常规注射成型的37．04％提高到48．53％；WAXD分析说明试样韧性的改善是由于振动注射成型生成了部分的β晶型。     

注射速度对制品成型结晶形态的影响

以某平板塑件为例,以聚丙烯（PP）为实验材料,通过成型取样、X射线衍射实验及数据处理技术相结合的方法研究了注射速度对制品结晶形态的影响规律及影响效应。结果表明,在正常情况下,PP塑件的结晶类型主要为α、β两种晶型;制品的结晶度随注射速度的增大存在极点,呈现倒V字形的变化趋势;制品整体取向度与晶格畸变量具有类似的变化趋势,均随注射速度的增大而增大,而晶粒尺寸的变化则与注射速度呈现负相关性;注射速度对制品晶粒的影响最为显著,结晶度影响其次,影响显著性顺序依次为晶粒尺寸>结晶度>晶格畸变>取向度>晶型,对于本试样,最佳注射速度应控制在180 mm/s。     

聚酰胺纤维无定形样品的制备及结晶度的测定

将初生尼龙66、尼龙6纤维束,装入样品夹内,用螺丝固定牢后,放入间苯酚溶剂,待纤维开始变得透明,立刻取出,这样就制成了标准无定形样品。用几种方法计算了结晶度,并比较和讨论了结果。我们制备的尼龙66无定形和结晶标样,用结晶度指数法能敏感地反应结晶度的变化,给出很好的结果,对尼龙6我们提出了简易计算方法,结果与结晶度指数法一致。     

注塑成型条件对聚甲醛制品冲击性能的影响

用精密注塑机加工成型聚甲醛制品，考察了注塑成型条件如注射压力、注射时间、冷却时间、模具温度、后处理条件等对制品冲击性能的影响，找到了最佳工艺条件，制得了冲击性能优良的聚甲醛制品。由扫描电镜观察、结晶度测定和Ｘ射线衍射分析表明，聚甲醛制品的冲击韧性与其局部缺陷、裂纹、结晶度、晶粒大小等有关，只有改善制品的均匀性，减少局部缺陷的产生控制结晶度和晶粒大小在适当范围，才能制得冲击性能优良的制品。     

聚丙烯注塑件结晶形态的研究

用X射线衍射法测定了注射成型聚丙烯的结晶度,并用偏光显微镜法观察了它的结晶形态。结果表明,聚丙烯结晶度随着距离浇口位置的增加而减小,并观察到表芯结构中纤维晶层的厚度随着注射温度的升高而减小。     

红外光谱法测定聚乙烯醇结晶度的研究

基于红外光谱技术,通过计算聚乙烯醇(PVA)在1 142,1 093 cm–1处的吸收峰面积,建立了一种测定PVA结晶度的傅立叶变换红外光谱(FTIR)分析方法。对比分析了不同制样方法所得的FTIR谱图;探讨了氢键对PVA结晶度的影响。结果表明,FTIR分析方法能有效测定PVA的结晶度;采用薄膜法制样更适合所建立的FTIR分析方法;延长退火时间、升高退火温度能减弱氢键对PVA结晶度的影响。     

高聚物结晶度计算公式中校正因子的讨论

本文对使用广角X-射线衍射方法测定高聚物结晶度计算公式的校正因子,进行了讨论与修正。根据本文给出的校正因子C(θ),k的计算方法和结晶度计算公式,按图解法可以较简便地求得一般结晶高聚物的结晶度。     

聚1-丁烯结晶度的实验测定

用差示扫描量热法(DSC)和密度法测定了聚1-丁烯的结晶度,并对2种方法测得的结晶度进行了线性拟合。结果表明,用密度法测得的结晶度相对于DSC法测得的结晶度要高,2种方法所测得的结晶度有较好的线性关系。     

注射成型工艺参数对PP制品结晶度影响的实验研究

利用5因素4水平正交试验表安排16组实验,通过对注射成型参数进行调节,研究了聚丙烯制品结晶度随成型工艺参数发生变化的规律。结果表明,对结晶度影响较显著的因素是保压压力,影响较大的因素是模具温度,熔体温度、保压时间和注射速度的影响较小。成型工艺参数对结晶度的影响主要是使分子在应力诱导下发生结晶,在成型过程中降低熵。     

液压脉动注射成型聚乳酸力学性能及生物降解性能的研究

在不同振动工艺参数下,研究液压脉动注射成型对聚乳酸(PLA)制品力学性能、结晶性能及生物降解性能的影响.结果表明,与普通注射成型相比,液压脉动注射成型的PLA制品拉伸强度提高了10.6%,冲击强度提高了29.7%,结晶度提高了11.9%.在蛋白酶K催化降解下,其生物降解过程是从表面侵蚀到内部整体侵蚀的逐步演变过程,制品总降解速率比普通注射成型的小.     

Crystallinity and microstructure in injection moldings of isotactic polypropylenes. Part II: Simulation and experiment

The injection moldings of isotactic polypropylenes with various molecular weights were simulated using finite difference method. In the simulations, the unified crystallization model proposed in our previous paper was applied. The prediction of crystallinity and microstructure development in the moldings was based upon the crystallization kinetics and the “competing mechanisms” for introducing various microstructure layers in the moldings. Extensive injection molding experiments were carried out. The pressure traces during the molding experiments were recorded. The crystallinity distribution in the moldings was determined using differential scanning calorimetry. The measurements on the microstructure embedded in the moldings were performed, including the thickness of the highly oriented skin layer and the gapwise distribution of the spherulite sizes. The measured data for the crystallinity and microstructure in the moldings were compared with the simulated results. The effects of molecular weight and processing conditions on the development of crystallinity and microstructure in the moldings were elucidated. Theoretical predictions were found to be in a good agreement with experimental measurements.     

Optical monitoring of polypropylene crystallization during injection molding

The nonisothermal crystallization of polypropylene resins, i‐PP, during injection molding, using an optical device inserted in the injection mold cavity was monitored. The device detected the change of optical properties which occurs in polymers during their crystallization process; thus the intensity of a laser beam after it passed through the crystallizing polymer was measured during an injection molding cycle. The collected light intensity after the end of the cycle was correlated with the morphologies and final crystallinity degree of the samples. The influence of nucleating agents and the change of the parameters of the injection molding process on the morphology and optical signals were also investigated. The morphologies were analyzed by polarized light optical microscopy, PLOM. The % of crystallinity of the samples was measured by wide angle X‐rays diffraction, WAXS. It was concluded that the optical device was sensible to different polymer crystallization kinetics, morphology type, and changes in the injection molding parameters. It was also found that the mold temperature and packing pressure and time were the factors that affected most the kinetics of crystallization of these polymers in this particular disk geometry. The WAXS results showed that the lower the final light intensity the higher the % of crystallinity in the samples. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

电磁动态注塑对等规聚丙烯增韧和增强研究

利用普通注射成型和电磁动态注塑机注射成型制备等规聚丙烯试样，并对其进行拉伸强度、冲击强度、差示扫描量热仪（DSC）和广角X射线衍射（WAXD）测试。对动态与稳态注射成型聚丙烯制品的力学性能进行了比较，并结合微观测试结果，深入探讨了制品微观结构与力学性能之间的关系。力学测试结果表明，动态成型制品的拉伸性能和冲击性能比稳态加工条件下都有所提高，尤其是制品冲击性能的提高幅度可以达到40％以上，实现了对制品的同时增强和增韧。DSC和WAXD测试表明，动态成型制品的结晶比稳态制品完善，并且晶粒尺寸也小于稳态制品。经过理论分析，认为结晶情况的改善是制品拉伸强度提高的原因，而晶粒细化则大幅度提高了制品的冲击强度。     

Primary structure and physical properties of poly(ethylene terephthalate)/poly(ethylene naphthalate) resin blends

The morphology and properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) that were injection molded under various conditions were studied. Under injection molding conditions that make it possible to secure transparency, blends did not show clear crystallinity at blending ratios of more than 20 mol% in spite of the fact that crystallinity can be observed in the range of PEN content up to 30 mol%. Because both transparency and crystallinity could be secured with a PEN 12 mol% blend, this material was used in injection molding experiments with various injection molding cycles. Whitening occurred with a cycle of 20 sec, and transparency was obtained at 30 sec or more. This was attributed to the fact that transesterification between PET and PEN exceeded 5 mol% and phase solubility (compatibility) between the PET and PEN increased when the injection molding time was 30 sec or longer. However, when the transesterification content exceeded 8 mol%, molecularly oriented crystallization did not occur, even under stretching, and consequently, it was not possible to increase the strength of the material by stretching. PET/PEN blend resins are more easily crystallized by stretch heat‐setting than are PET/PEN copolymer resins. It was understood that this is because residual PET, which has not undergone transesterification, contributes to crystallization. However, because transesterification reduces crystallinity, the heat‐set density of blends did not increase as significantly as that of pure PET, even in high temperature heat‐setting. Gas permeability showed the same tendency as density. Namely, pure PET showed a substantial decrease in oxygen transmission after high temperature heat‐setting, but the decrease in gas permeability in the blend material was small at heat‐set temperatures of 140°C and higher.     

Effect of crystallization and interface formation mechanism on mechanical properties of film‐insert injection‐molded poly(propylene) (PP) film/PP substrate

A previous study has shown that the adhesion between the film and substrate of film‐insert injection‐molded poly(propylene) (PP) film/PP substrate was evident with the increases in barrel temperature and injection holding pressure. In this second part of the research work, the crystallinity at the interfacial region (i.e., region between the film and the injected substrate) was extensively studied using FTIR imaging, polarized light microscopy, and DSC in an attempt to determine the level of influence that crystallinity has on the interface and bulk mechanical properties. Consequently, a more thorough and clearer picture of the influence of the inserted film on the interfacial crystallinity and subsequently the substrate mechanical properties, such as peel strength and impact strength, has been revealed. The initial proposition that crystallinity could enhance film–substrate interfacial bonding has been confirmed, judging from the higher peel strength with increasing crystallinity at the interfacial region. Nevertheless, the change in crystallinity was not only confined to the interfacial region. With the film acting as heat‐transfer inhibitor between the injected resin and the mold wall, the total crystal structure of the substrate was substantially altered, which subsequently affected the bulk mechanical properties. The lower impact strength of film‐insert injection‐molded samples compared to that of samples without film inserts provided evidence of how the film could impart inferior properties to the substrate. The difference in cooling rate between the substrate and film might also cause other defects such as warpage and/or residual stress build‐up within the product. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 294–301, 2005     

An X‐ray scattering study of water‐conditioned injection‐molded starch during isothermal heating

The in situ structure variation of injection‐molded starch (as processed and after water conditioning) during heat treatment was investigated by means of wide‐angle X‐ray scattering using synchrotron radiation. Results confirm that the crystal structure of potato starch is destroyed after injection molding, while as‐processed corn starch preserves some degree of crystallinity. This residual crystallinity in corn starch is related to the crystalline Vh‐form, made of complexes of amylose with lipids. Furthermore, it is shown that both starch types can develop crystallinity by water conditioning: potato starch yields the crystal B‐form, while corn starch yields the crystal A‐form coexisting with the persistent Vh‐form. Upon isothermal heating of samples under vacuum, a rapid decrease of crystallinity, which is a function of both time and treatment temperature, is detected. Crystallinity variations are discussed in terms of water evaporation, the leveling‐off values of crystallinity being dependent on the temperature of the isothermal treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 17–21, 2003