动态保压注射成型技术对PA6／EPDM-g-MA共混物相形态与力学性能的影响

采用动态保压注塑成型技术来控制分散相相形态和橡胶粒子在基体中的取向排列。纯尼龙。动态样与静态样具有相同的冲击强度。在加入橡胶后，动态样与静态样的冲击强度变化趋势基本一致，在橡胶含量为20％t时。体系完成脆韧转变冲击强度达到最大，在橡胶含量为30％和40％时冲击强度又下降。但与静态样相比。当橡胶含量为10％t时，动态样与静态样的冲击强度一致。而当橡胶含量超过10％时，动态样的冲击强度较静态样高。结合平行于熔体流动方向的SEM照片，在橡胶含量为10％时，动态样中的橡胶粒子与静态样一样并未被拉长与取向，而在橡胶含量超过10％时，动态样剪切层中的橡胶粒子被拉长且沿熔体流动方向取向。实验表明。在改善共混物界面相容性的基础上。适当的低剪切应力场能进一步提高橡胶分散相对冲击强度的贡献。     

纳米CaCO3填充ABS/PP合金复合物研究

通过熔融共混使纳米CaCO3粒子周围包覆上一层TPE橡胶,制备出纳米CaCO3母料,用其与PP、ABS共混复合制备出ABS/PP合金纳米填料复合物.该复合材料力学性能及熔体流动性能测试结果表明,纳米CaCO3含量在试验用量范围内,ABS纳米CaCO3复合物的拉伸强度随填料含量的增加而增加,当母料含量为17%,母料中纳米CaCO3填料含量为60%左右时有较佳的冲击性能;ABS/PP纳米CaCO3复合物在PP含量9%～10%时有最好的拉伸强度和冲击强度;纳米CaCO3填料含量对复合物的拉伸强度影响不大,随其用量增加对冲击强度有明显的提高;熔体流动性能在PP含量10%左右时达最大,但随填料含量增加而下降.     

茂金属聚乙烯与通用聚乙烯共混物熔体的流变行为研究

用茂金属线型低密度聚乙烯(mLLDPE)与通用聚乙烯(LDPE、LLDPE)进行共混,测定了共混物的熔体质量流动速率(MFR);研究了共混物熔体的熔体强度和剪切敏感性.结果发现:当质量分数超过20%的mLLDPE与高熔体质量流动速率(MFR)的通用聚乙烯共混时,或者质量分数小于40%的mLLDPE与低MFR的通用聚乙烯共混时,共混物熔体的流动性会小于单一共混组分,除了在与一种LDPE共混时mLLDPE加入质量分数为10%的一种共混物外,其他共混物的熔体强度都超过单个共混组分.mLLDPE/LLDPE共混物熔体的剪切敏感性高于LLDPE.     

中等分子量PP在动态保压单向流动场中的结构与性能研究

利用自行研制的能够方便改变工艺条件的新型动态保压注射成型(DPIM)装置,研究了中等分子量聚丙烯(PP)注射成型试样的结构与性能.研究表明:所得中等分子量PP试样的结构与性能与注射成型过程中的工艺条件有密切关系,如:振动压力、熔体温度等.振动压力、熔体温度对试样性能的影响呈二次曲线关系,拉伸强度随着振动压力的升高先提高而后减小,有一个最大值.拉伸强度同样也随着熔体温度的升高先提高后减小,有一个最大值.DSC曲线表明:动态试样熔融呈现明显的脊纤维晶和片晶两个熔融峰,而静态试样呈现明显的片晶熔融单峰.SEM照片显示静态试样剪切层结晶形态主要为球晶结构,动态试样剪切层产生明显的高度取向串晶结构.所有的测试结果表明:中等分子量PP在动态保压单向流动场中所得试样内部结晶由静态试样中的球晶转变成了串晶,且性能明显提高.     

熔体状态对等规聚丙烯结晶行为的影响

通过Linkam CSS450剪切热台控制等规聚丙烯(iPP)的熔融温度,研究了不同熔融温度下熔体有序程度对iPP静态结晶和剪切诱导结晶行为的影响。结果表明:降低熔融温度能有效提高iPP静态结晶动力学;对于剪切诱导结晶过程,随着熔融温度的降低,iPP分子链取向程度得到提高,相同剪切速率下,低温熔融样品的分子链取向程度较高;熔体中有序结构含量随熔融温度升高而降低,这些有序结构能沿流动方向进行取向排列。     

MBS树脂胶含量对PC/MBS合金性能影响

PC/MBS合金熔体流动速率、拉伸强度、冲击强度和维卡软化温度的变化与MBS树脂中橡胶含量的多少相关。实验表明:MBS树脂中橡胶含量增加,合金的拉伸强度和维卡软化温度均降低,而冲击强度增大;实验中改变MBS树脂的树脂用量及其橡胶含量可以调节合金的流动性;橡胶含量为30%的MBS树脂可以很好地提高PC/MBS合金的冲击强度。     

剪切对PP/HDPE共混体系微孔发泡成型的影响

在熔体流动方向垂直叠加一个轴向脉动剪切,研究转子转动产生的剪切和轴向脉动剪切对PP/HDPE共混体系微孔发泡成型的影响。研究结果表明,随着转子转速增加,泡孔尺寸减小,气泡成核密度增大。但是转子转速过快,泡孔沿剪切的方向被拉长,泡孔取向严重,泡体质量变差。在熔体流动方向垂直叠加一个轴向脉动剪切以后,泡孔的取向现象减小,泡孔逐渐趋于圆形,泡孔结构得到改善。而且随着振动振幅和频率的增加,泡孔直径减小,泡孔密度增加。     

FEP/PP共混物流动性能的研究

应用熔体流动速率仪考察了口模直径、聚丙烯(PP)含量、剪切速率及温度对聚全氟乙丙烯(FEP)/PP共混物熔体的流动性能的影响.结果表明,在试验条件下,熔体的剪切流动服从幂律定律;熔体的表观温度对温度的依赖性符合Arrhenius方程;当PP的质量分数(w)小于10%时,熔体的表观粘度随着w的增加急剧下降,w大于10%时,趋于平缓;熔体的表观粘度随着口模直径的增加而非线性的增加.     

PA6/BIIR动态硫化合金的制备、性能与应用

利用动态硫化法制备尼龙(PA)6/溴化丁基橡胶(BⅡR)合金,通过对其拉伸强度、冲击强度及熔体流动速率(MFR)等性能进行测试,讨论了马来酸酐(MAH)对合金力学性能和流动性能的影响,通过扫描电子显微镜观察合金冲击断面的形貌。结果表明,当MAH的含量为0.5份时,合金的力学性能和流动性能最好,此时的拉伸强度为19.8 MPa,断裂伸长率为15%,缺口冲击强度为26.1 kJ/m2,MFR为0.15 g/(10 min)。该合金可以作为阻气材料的衬里使用。     

聚碳酸酯/丙烯腈-丁二烯-苯乙烯合金冲击性能研究

使用双螺杆挤出机制备聚碳酸酯/丙烯腈-丁二烯-苯乙烯(PC/ABS)合金,综合分析PC熔体流动速率、ABS胶含量、PC与ABS比例、增韧剂等因素对合金冲击强度的影响。结果表明:PC的熔体流动速率越小,合金冲击强度越高。在实验范围内,不同熔体流动速率PC制备的合金冲击强度最大差距达10kJ/m~2;PC/ABS质量比为65/35时,冲击性能最佳;ABS胶含量的增加有利于合金冲击性能的改善,使用胶质量分数45%的ABS制备的合金冲击性能最佳;甲基丙烯酸甲酯-丁二烯-苯乙烯(MBS)添加质量分数6%时对合金增韧效果最明显,合金冲击性能提高15%。     

Phase morphology and toughening mechanism of polyamide 6/EPDM-g-MA blends obtained via dynamic packing injection molding

One of the most important findings in polymer-toughening is known as the critical matrix ligament thickness (τ_c) theory, which is directly related to both rubber concentration and average size of particles. All these studies assume that rubber particles are spherical and randomly distributed in the matrix. Rubber particles may be stretched and oriented along the shear flow direction in real processing. In this paper the effect of stretched and oriented rubber particles on the impact strength of PA6/EPDM-g-MA blends have been studied via dynamic packing injection molding (DPIM). The impact strength of specimens obtained by DPIM was found substantially increase at all the blends investigated, compared with the one obtained via conventional injection molding. Particularly, more than 30 kJ m⁻² increase of the impact strength was observed for specimens with a higher rubber content (more than 15 wt%). SEM results showed a remarkably decrease of rubber particle size and more uniform dispersion of the dynamic molded specimens. This can be attributed to the shear induced reaction at the interface between polyamide 6 and EPDM-g-MA during the packing stage. The rubber particles were found stretched along the melt shear flow direction when it is content above 15 wt%. A master curve can be also constructed by plotting the impact strength versus the inter-particle distance, indicating that Wu's criterion still works for blends with stretched and oriented rubber particles when the crack propagation direction is perpendicular to the orientation direction of rubber particles. The observed higher impact strength in dynamic specimens could be due to, in part, the enhanced flexural stiffness, which will absorb more energy during impact process when the fracture of IZOD bars is incomplete, but more importantly due to the existence of the stretched and oriented rubber particles, which are more efficient in slowing the velocity of crack propagation and thus cause higher impact resistance when the fracture propagation direction is perpendicular to the rubber oriented direction.     

Dependence of impact strength on the fracture propagation direction in dynamic packing injection molded PP/EPDM blends

In order to further understand the brittle-ductile (B-D) transition in PP/EPDM blends, a shear stress field achieved via dynamic packing injection molding was used to control the rubber particles as elongated and orientated in the PP matrix. The impact strength of the blends was measured in three fracture directions, namely, along the shear flow direction, perpendicular to and oblique (45°) with the flow direction. A definite B-D transition of impact strength was found at 20 wt% of EPDM content along the shear flow direction. About 10 times increase of impact strength was observed at the B-D transition. However, a B-D transition and then a decrease of impact strength brittle-ductile-brittle (B-D-B) was found as increasing of EPDM content in the impact direction perpendicular to and oblique with the flow direction. One observes a big increase of impact strength at 20-30 wt% of EPDM content (B-D transition) from 10-20 to 70-80 kJ/m², then a sharp decrease of impact strength is seen when EPDM content reaches to 30-45 wt% (D-B transition) from 70-80 to 40-50 kJ/m². Correspondingly, there exists a change of rubber particles from roughly spherical shape to highly elongated and oriented shape at D-B transition. SEM shows a very smooth fractured surface when fracture propagation is along or oblique with the shear flow direction, but a lay-by-layer fracture behavior when fracture propagation is perpendicular to the shear flow direction. Our results suggest that the impact fracture direction with respect to the orientation direction play an important role to determine the impact strength. Wu's theory holds true as long as the rubber particles are roughly spherical when viewed in the same direction with fracture propagation direction, but no longer valid when dispersed rubber particles are elongated and oriented when viewed in the direction perpendicular to or oblique with the fracture propagation direction.     

Super polyolefin blends achieved via dynamic packing injection molding: the morphology and mechanical properties of HDPE/EVA blends

As a part of long-term project aimed at super polyolefin blends, in this work, we report the mechanical reinforcement and phase morphology of the blends of high-density polyethylene (HDPE) and ethylene vinyl acetate (EVA) achieved by dynamic packing injection molding. The shear stress (achieved by dynamic packing injection molding) and interfacial interaction (obtained by using EVA with different VA content) have a great effect on phase morphology and thus mechanical properties. The super HDPE/EVA blends having high modulus (1.9–2.2 GPa), high tensile strength (100–120 MPa) and high impact strength (six times as that of pure HDPE) have been prepared by controlling the phase separation, molecular orientation and crystal morphology of the blends. The phase inversion was also found to shift towards lower EVA content under shear stress. The enhancement of tensile strength and modulus originates from the formation of oriented layer, while the high impact strength is related to shear induced phase morphology. DSC studies indicated that the shish kebab crystal structure that also contributes to the enhancement of tensile strength is formed in the oriented layer. The dramatic improvement of impact strength may result from the formation of microfibers and elongated EVA particles along the flow direction. Wu's toughening theory was found non-applicable for the elongated and oriented rubber particles, and a brittle–ductile–brittle transition was observed with increasing EVA content.     

Adding EPDM Rubber Makes Poly(propylene) Brittle

To better understand the mechanism of polymer‐toughing with rubber and the critical matrix ligament thickness theory developed by Wu, the rubber particle shape was controlled as elongated and oriented instead of spherical in PP/EPDM blends via dynamic packing injection molding. For the first time, the brittle‐ductile‐brittle transition was observed with increasing rubber content. This result clearly indicates that Wu's theory applies only for cubic or spherical particles but not for elongated and oriented particles. The higher stress concentration will be expected at the tip, which causes blends to fail in brittle mode. More work is needed to verify this expectation.     

Characterization of PA6/EPDM-g-MA/HDPE ternary blends: The role of core-shell structure

In this work, the relationship between properties and morphologies of PA6/EPDM-g-MA/HDPE ternary blends was studied. Two processing methods (one- and two-step methods) were applied to prepare the PA6/EPDM-g-MA/HDPE ternary blends. The dependence of the phase morphology on interfacial interaction and processing method was discussed here. It was found that core-shell morphology (core: HDPE, shell: EPDM-g-MA in PA6 matrix) appeared in PA6/EPDM-g-MA/HDPE ternary blends, and in comparison to the blend prepared by one-step method, the core-shell morphology with thicker EPDM-g-MA shell appeared in the blend prepared by two-step method. In this case, a super toughened PA6 ternary blends with the Izod impact strength of 72.51 kJ/m² which is 4–5 times higher than PA6/EPDM-g-MA binary blend and 9–10 times higher than pure PA6 could be achieved. Moreover, the rheological results indicated that the storage modulus of ternary blends was heavily dependent on the phase morphology. The core-shell structure with thicker EPDM-g-MA shell would weaken the contribution of interfacial energy to the storage modulus of ternary blends.     

Effects of clay on phase morphology and mechanical properties in polyamide 6/EPDM-g-MA/organoclay ternary nanocomposites

In this study, both organoclay and EPDM-g-MA rubber were used to simultaneously improve the toughness and stiffness of polyamide 6 (PA6). We first prepared PA6/EPDM-g-MA/organoclay ternary nanocomposites using melt blending. Then the composites were subjected to traditional injection molding and so-called dynamic packing injection molding. The dispersion of clay, phase morphology, crystallinity and orientation of PA6 as well the mechanical properties were characterized by WAXD, SEM, DSC, 2D-WAXS and mechanical testing, respectively. The effects of clay on phase morphology and mechanical properties of PA6/EPDM-g-MA blends could be summarized as follows: (1) weakening interphase adhesion between PA6 and EPDM-g-MA rubber particles, resulted in increasing of rubber particle size, as the clay and rubber contents are low; (2) preventing coalescence of rubber domains, arisen in decreasing of rubber particle size, as the clay and rubber contents are high; (3) the blocking effect on the overlap of stress volume around rubber particles caused broadening of the brittle-ductile transition region and decrease of toughness, and (4) the effective stress transfer leading a better reinforcement when the interparticle distance is smaller than the critical value.     

Microscopic Deformation Behavior and Crack Resistance Mechanism of Core–Shell Structures in Highly-Toughened PP/PA6/EPDM-g-MA Ternary Blends

Highly-toughened blends, comprising polypropylene, polyamide 6, and maleic anhydride-grafted ethylene-propylene-diene monomer rubber (PP/PA6/EPDM-g-MA), of core–shell morphology are prepared and impact of microstructural development, at different PA6:EPDM-g-MA weight ratios (fixed at 30 wt%), on macroscopic mechanical and fracture characteristics of blends is studied through in-depth analysis of micromechanical deformations operating in the blends. The role of dispersion state of modifier domains on nucleation and evolution of various microscopic deformations accompanying the fracture process under impact and quasi-static fracture tests is closely examined. Increase in EPDM-g-MA:PA6 ratio develops agglomerated core–shell domains in the form of extended island-like structures. While impact data show significant synergistic toughening effect of dispersed composite domains in ternary blends compared with PP/EPDM-g-MA (70/30) binary blend, fracture works show a sole dependence on rubbery fraction. Fractography examinations reveal deformation of dispersed domains, development of multiple voids, and highly deformed craze-like void-fibrillar structures within core–shell structures as well as at their interfaces with surrounding matrix. The importance of deformation zones in activation and promotion of matrix shear yielding is clarified, while their function as crack nucleation and subsequent crack propagation trajectories is highlighted. The stability of void-fibrillar zones is found essential for extensive plastic deformation and premature failure prevention.     

Three-dimensional phase morphologies in HDPE/EVA blends obtained via dynamic injection packing molding

The formation of phase morphology of injection molded HDPE/EVA blends, under the effect of shear stress, has been investigated in detail. The shear stress was induced by dynamic packing injection molding, by which a specimen is forced to move repeatedly in the model by two pistons that move reversibly with the same frequency during cooling. Two kinds of EVA with VA content 16 wt% (16EVA) and 33 wt% (33EVA) were used to investigate the effect of interfacial tension. The phase morphology was viewed both parallel and perpendicular to the shear flow direction, so one can get an overall three-dimensional phase morphology. Low shear stress provided by the pistons has a substantial effect on the phase morphology along the flow direction but is insignificant in the direction perpendicular to the flow direction. Generally, a much elongated and layer-like structure is formed along the flow direction, and spherical droplet-like morphology is formed perpendicular to the flow direction, and the degree of deformation of rubber particles also depends upon their size and elasticity as well as on the interfacial properties between matrix and dispersed phase. For static samples of HDPE/16EVA blends (without shearing), only droplet morphology is formed as 16EVA content increases from10 to 40 wt%. However, under the effect of shear stress (dynamic samples), both droplet and cylinder morphologies can be formed depending on the volume ratio. For static samples of HDPE/33EVA blends, not only droplet, but also cylinder and co-continuous morphology (perpendicular to flow direction) can be formed depending on the volume ratio. For dynamic samples of HDPE/33EVA blends, droplet, cylinder and co-continuous network (co-continuous in both parallel and perpendicular to flow direction) can be formed under the effect of shear stress. The formation of phase morphology is discussed based on interfacial interaction, viscosity ratio, shear stress, and phase inversion.     

剪切作用下POE-g-MAH和PP-g-MAH对PA1010/PP共混物的增容作用

采用熔融共混的方法制备了聚酰胺1010/聚丙烯（PA1010/PP）共混物,通过扫描电镜、力学性能和差示扫描量热等方法研究了剪切作用下马来酸酐接枝乙烯-辛烯共聚物（POE-g-MAH）和马来酸酐接枝聚丙烯（PP-g-MAH）对PA1010/PP共混物的增容作用。结果表明,同样条件下,PP-g-MAH增容体系的相区尺寸较小,相界面更模糊,PP相的结晶温度和结晶度明显提高,共混物的拉伸强度和冲击强度均高于非增容体系。而POE-g-MAH增容体系的相区尺寸相对较大,PP相的结晶温度和结晶度明显降低,共混物只有冲击强度明显高于非增容体系,拉伸强度略低于非增容体系。     

Studies on blends of high‐density polyethylene and polypropylene produced by oscillating shear stress field

Tensile strength and morphology of blends of high‐density polyethylene (HDPE) and polypropylene (PP) obtained by oscillating packing injection molding were investigated via Universal Testing Machine, DSC, and SAXS. Tensile strength is greatly enhanced from 24.5 MPa to more than 90 MPa for pure HDPE and for blends with PP content less than 10 wt %. There exists a sharp decrease of tensile strength when PP content is more than 10 wt %. The shear‐induced morphologies with core in the center, oriented zone surrounding the core and skin layer are observed in the cross‐section areas of the samples. Interestingly, a sharp decrease of oriented zone is seen when PP content is more than 10 wt %, associated with the sharp decrease of tensile strength. DSC result shows double melting peaks with a high‐temperature melting peak that is not present in the endotherm obtained from the central core and obtained from the samples by static packing injection molding, which indicates the existence of shish‐kebab structure in the oriented zone. However, there is no difference of crystallinity between the samples by oscillating and by static packing injection molding. SAXS was used to analyze the complicated morphologies induced by shear stress, and results show that the crystal thickness could be greatly increased under shear stress. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 58–63, 2002