Effect of dispersed phase on the morphology of in situ microfibrils and the viscoelastic properties of its composite via direct extrusion

A triangle arrayed triple‐screw extruder was used to prepare in situ polypropylene (PP) microfibrillar composites (MFCs) by direct extrusion, in which polyamide 6,6 (PA66) and poly(butylene terephthalate) (PBT) were used as dispersed phases while PP as matrix phase. The morphological evolution of the dispersed phase were investigated by SEM through taking samples along the extruder from different positions. The results showed that the fibrillating mechanism of PA66 was entirely different from that of PBT. Dynamic oscillatory shear rheological properties were used to analyze the effect of different types of in situ microfibrils on the rheological properties of MFCs. The obtained results showed that the storage modulus and complex viscosity of both PP/PA66 and PP/PBT MFCs were improved with increasing fibrillar aspect ratios. The loss tangent tan δ at low frequencies decreased with the increase of fibrillar aspect ratio. Moreover, the gel point concentration of PP/PA66 composite was lower than that of PP/PBT composite. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46286.     

增容作用对PP/PA6原位微纤复合材料形貌及性能的影响

以马来酸酐接枝聚丙烯（PP-g-MAH）为增容剂,采用熔融挤出?热拉伸法制备了聚丙烯（PP）/聚酰胺6（PA6）/PP-g-MAH原位微纤复合材料。研究了复合材料的微观相形态以及结晶、流变和力学性能。结果表明,加入0.5 %（质量分数,下同）的PP-g-MAH有利于大长径比PA6微纤的形成;而当PP-g-MAH的含量继续增加时,相界面相容性的提高反而阻碍了微纤的生成;加入0.5 % PP-g-MAH的PP/PA6原位微纤复合材料在动态流变特性中呈现出很强的弹性响应,并且其结晶和力学性能显著改善。     

Developing electrically conductive polypropylene/polyamide6/carbon black composites with microfibrillar morphology

We have established that the PP/PA6/CB composite with 3D microfibrillar conducting network can be prepared in situ using melt spinning process. CB particles preferably were localized at the interface between polypropylene as the matrix and PA6 microfibrils, which act as the conducting paths inside the matrix. The percolation threshold of the system reduced when aspect ratio of the conducting phase was increased by developing microfibrillar morphology. The effect of annealing process on the conductivity of PP/PA6/CB composite with co‐ continuous and microfibrillar morphologies was studied. It was observed that, annealing process forces CB particles towards the interface (2D space) of PP and PA6 co‐continuous phases, and percolation threshold and critical exponent of classical percolation theory will be decreased, while the conductivity of conducting composite with microfibrillar morphology was not affected considerably by annealing process at temperatures either higher or lower than the melting point of the PA6 microfibrils. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Compatibilization of polypropylene/nylon 6 blends with a polypropylene solid‐phase graft

The compatibilization of polypropylene (PP)/nylon 6 (PA6) blends with a new PP solid‐phase graft copolymer (gPP) was systematically studied. gPP improved the compatibility of PP/PA6 blends efficiently. Because of the reaction between the reactive groups of gPP and the NH₂ end groups of PA6, a PP‐g‐PA6 copolymer was formed as a compatibilizer in the vicinity of the interfaces during the melting extrusion of gPP and PA6. The tensile strength and impact strength of the compatibilized PP/PA6 blends obviously increased in comparison with those of the PP/PA6 mechanical blends, and the amount of gPP and the content of the third monomer during the preparation of gPP affected the mechanical properties of the compatibilized blends. Scanning electron microscopy and transmission electron microscopy indicated that the particle sizes of the dispersed phases of the compatibilized PP/PA6 blends became smaller and that the interfaces became more indistinct in comparison with the mechanical blends. The microcrystal size of PA6 and the crystallinity of the two components of the PP/PA6 blends decreased after compatibilization with gPP. The compatibilized PP/PA6 blends possessed higher pseudoplasticity, melt viscosity, and flow activation energy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 420–427, 2004     

In situ fibrillation of isotactic polypropylene in ethylene-vinyl acetate: Toward enhanced rheological and mechanical properties

In situ microfibrillar reinforced composites with ethylene-vinyl acetate (EVA) as matrix and isotactic polypropylene (iPP) as dispersed fibrils were successfully fabricated by multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs). Four types of EVA with different apparent viscosity were utilized to study the influence of viscosity ratio on the morphology and mechanical properties of EVA/iPP in situ microfibrillar blends. The scanning electron micrographs revealed that the dividing–multiplying processes in LMEs could effectively transform the morphology of iPP phase into microfibrils and the morphology of iPP microfibrils strongly depended on the viscosity ratio. Higher viscosity ratio was favorable for formation of finer microfibrils with narrower diameter distribution. The morphology development of iPP with different viscosity ratio greatly affected the rheological and mechanical properties of EVA/iPP blends. The dynamic rheological results shown that the iPP microfibrils were helpful to increase the storage modulus and loss modulus. The tensile test indicated that the mechanical properties of EVA/iPP blends were controlled by the morphology of iPP phase and the polarity of EVA matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47557.     

Effect of thermotropic copolyesteramide on the properties of polyamide‐66/liquid crystalline copolyester composites

Liquid crystalline copolyester‐polyamide 66 (LCPES/PA66) composites compatibilized by liquid crystalline copolyesteramide (LCPEA) were prepared by injection molding. The LCPES employed was a commercial copolyester, Vectra A950, and the LCPES was a semiflexible thermotropic copolyesteramides based on 30 mol% of p‐amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). Thermal analysis, mechanical characterization, and morphological investigations were conducted on the blends. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) tests showed that LCPEA is an effective compatibilizer for the LCPES/PA66 composites. The mechanical measurements showed that the stiffness, tensile strength and Izod impact strength of the in‐situ composites are improved by adding LCPEA because of the compatibilization and reinforcement to LCPES/PA66 composites. However, the properties improvement vanished when LCP content reached 10 wt%. The drop weight dart impact test was also applied to analyze the impact fracture characteristics of these composites. The results showed that the maximum impact force (F_max), crack initiation and propagation energy all improved with the addition of a small percent of LCPEA. From these results, it appeared that LCPEA prolongs the time for crack initiation and propagation. It also increases the energies for crack initiation and propagation, thereby leading to toughening of the LCPES/PA66 in‐situ composites. Finally, the correlation between the mechanical properties and morphology of the composites is discussed.     

聚丙烯熔融接枝马来酸二丁酯增容聚丙烯／尼龙6的研究

研究了聚丙烯（ＰＰ）与马来酸二丁酯（ＤＢＭ）的接枝共聚物ＰＰｇＤＢＭ对聚丙烯／尼龙６（ＰＰ／ＰＡ６）共混物的增容作用。研究表明,ＰＰｇＤＢＭ是ＰＰ／ＰＡ６共混体系的有效增容剂,由于共混过程中就地生成ＰＰｇＰＡ６,改善了共混物的相容性,增加了两相界面的粘合,使分散相粒径减小,分散更均匀,提高了共混物的力学性能。增容剂接枝率的高低对增容效果有一定影响,接枝物中残留单体不影响增容效果     

Morphologies and properties of polycarbonate/polyethylene in situ microfibrillar composites prepared through multistage stretching extrusion

The sheets of polycarbonate (PC)/polyethylene (PE) in situ microfibrillar composites are successfully prepared directly through multistage stretching extrusion with an assembly of laminating‐multiplying elements (LMEs) instead of the secondary processing. The morphological development of the PC dispersed phase in PE matrix with increasing the number of LMEs during multistage stretching extrusion investigated by scanning electron microscope shows that core‐skin structure of the microfibrillar PC/PE composites during multistage stretching extrusion with 4 LMEs is weakened, and the diameter of the PC microfibrils is relatively more uniform, indicating that the shear field in LMEs greatly affects the morphology of PC dispersed phase in PE matrix. The tensile, crystalline, melting, orientation and rheological behavior of the PC/PE microfibrillar composites are also investigated. The results show that the PC microfibrils are helpful to increase complex viscosity and yield stress of the PE/PC composites. In addition, it is found that the glass transition temperature of PC in PE matrix reduced with increasing the number of LMEs during dynamic rheological testing. It is coincided with the results of DSC analysis of the PC/PE composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40108.     

Morphology and Mechanical Properties of Normal Blends and In-Situ Microfibrillar Composites from Low-Density Polyethylene and Poly(ethylene terephthalate)

In this work, normal blends, microfibrillar blends and composites were prepared from low density polyethylene (LDPE) and poly(ethylene terephthalate) (PET) in 85/15 and 75/25 w/w% ratio in the presence and absence of a compatibilizer polyethylene grafted with maleic anhydride (PE-g-MA). The microfibrillar composites (MFCs) were prepared using extrusion – drawing – isotropization technique. The morphology development of the microfibrillar blends and composites was studied using scanning electron microscopy (SEM). The presence of 5 wt% PE-g-MA compatibilizer affected the continuity of the fibrils differently in 75/25 and 85/15 w/w% microfibrillar blends. In the case of normal blends the addition of compatibiliser reduced the size of the dispersed PET phase. The presence of PET microfibrils improved the tensile properties of the microfibrillar composites. The normal blends exhibited a relatively ductile failure during tensile loading in comparison with the microfibrillar composites. The microfibrillar nature of the dispersed phase was found to improve the stiffness of the composite rather than their impact strength.     

Crystallization behavior of PP/PP‐g‐MAH/GFR PA66 blends: Establishment of their continuous‐cooling‐transformation of relative crystallinity diagrams

Polypropylene/polypropylene‐grafted‐maleic anhydride/glass fiber reinforced polyamide 66 (PP/PP‐g‐MAH/GFR PA 66) blends‐composites with and without the addition of polypropylene‐grafted‐maleic anhydride (PP‐g‐MAH) were prepared in a twin screw extruder. The effect of the compatibilizer on the thermal properties and crystallization behavior was determined using differential scanning calorimetry analysis. The hold time was set to be equal to 5 min at 290°C. These conditions are necessary to eliminate the thermomechanical history in the molten state. The crystallization under nonisothermal conditions and the plot of Continuous‐Cooling‐Transformation of relative crystallinity diagrams of both PP and PA 66 components proves that PP is significantly affected by the presence of PP‐g‐MAH. From the results it is found that an abrupt change is observed at 2.5 wt % of PP‐g‐MAH as a compatibilizer and then levels off. In these blends, concurrent crystallization behavior was not observed for GFR PA66. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1620–1626, 2007     

Effect of graphite nanoplatelets on fracture behavior of HDPE/PA66 microfibrillar composites

Effect of in situ formation of PA66 fibrils and modification with graphite nanoplatelets (GNP) on fracture behavior of the high‐density polyethylene (HDPE)‐matrix microfibrillar composites (MFC) has been evaluated using tensile impact strength (TIS) and J‐integral methods. According to J‐integral, the main mechanism of failure is unstable crack growth; dissimilar layout of both methods causes different contribution of reinforcement with GNP and PA66 fibrils to fracture process evaluated. More marked orientation and parallel loading lead to increase in impact energy by both GNP and fibrils in TIS; on the other hand, much lower contribution of fibres and even negative effect of GNP pre‐blended in HDPE was found for J‐integral as a consequence of load acting in perpendicular direction. The fact that lower addition of GNP pre‐blended in PA66 does not deteriorate impact behavior indicates that such modification of MFC is an efficient way to get materials with enhanced, well‐balanced parameters. POLYM. ENG. SCI., 59:382–388, 2019. © 2018 Society of Plastics Engineers     

From polymer blends to in situ polymer/polymer composites: Morphology control and mechanical properties

In situ polymer/polymer short fiber composites were generated by a two‐step process. In the first step, a polyamide (PA) dispersed phase is blended with a polypropylene (PP) matrix in a twin‐screw extruder at a temperature at which both polymers are in molten state. The extrudate was then stretched at the die exit to generate long and thin fibers of PA in the PP matrix well oriented in the direction of flow. Adhesion between the phases was promoted by addition of PP grafted with maleic anhydride (PP‐g‐MA). During the second step, the chopped extrudates were molded by injection or compression molding at a temperature at which PA in the form of fibers is in the solid state and the PP matrix is molten. The control of the formation of such ultrafine fibers was obtained by quantitative analyses for the deformation of the minor PA‐phase during twin‐screw extrusion and stretching at the exit of the die that involve both shear and extensional flows. Morphology and mechanical properties of such polymer/polymer composites were compared to equivalent blends with dispersed spherical particles‐type morphology prepared in a batch mixer device.     

Factors influencing the fiberization and mechanical properties of polypropylene/polyamide 66 in situ composites

In situ composites based on immiscible polypropylene (PP)–polyamide 66 (PA66) melt blends were prepared through extrusion, drawing, quenching and then injection molding. The results show that both draw ratio (λ) and compatibilizer content (Cg) have significant influences on the PA66 fiberization and mechanical properties of the composites. PA66 fiberization in the PP matrix is realized during the melt drawing through a die. The increase in λ is favorable for fiberization of the dispersed phase, which leads to a large increment of impact strength (a_k) and some improvement of the tensile strength (σ_t) of the composites. Nevertheless, the elevated Cg is unfavorable for fiberization, which results in the reduction of a_k whereas σ_t is enhanced, apparently due to the improvement of interfacial adhesion. The coalescence effect of PA66 droplets during drawing plays a key role in fiberization. The σ_t and a_k of the composites are primarily dictated by the interfacial structure and fiber morphology, respectively, which determine the variation rules of these properties with λ or Cg. Copyright © 2003 Society of Chemical Industry     

In situ compatibilization of polypropylene/polystyrene blend by controlled degradation and reactive extrusion

In situ compatibilization of polypropylene (PP) and polystyrene (PS) was achieved by combinative application of tetraethyl thiuram disulfide (TETD) as degradation inhibitor and di‐tert‐butyl peroxide as degradation initiator in the process of reactive extrusion. The PP/PS blends obtained were systematically investigated by rheological measurement, scanning electron microscopy, and differential scanning calorimetry. The results indicate that peroxide‐induced degradation of PP can be effectively depressed by adding TETD, which may favor the formation of PP‐g‐PS copolymer during melt processing. The PP‐g‐PS copolymer formed may act as an in situ compatibilizer for PP/PS blends, and subsequently decreases the size of dispersed PS phase and changes both rheological and thermal properties of the blends. Based on the present experimental results, the mechanisms for the controlled degradation of PP and in situ formation of PP‐g‐PS copolymer in the PP/PS blends have been proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A quantitative estimation of the extent of compatibilization in heterogeneous polymer blends using their heat capacity increment at the glass transition

In this paper a new method based on the determination of heat capacity increment at the glass transition (ΔCp) is presented to quantify the effectiveness of compatibilizers for immiscible polymer blends. In order to show the validity of the method, two immiscible blends, polypropylene–poly(ethylene terephthalate) (PP–PET) and PP–polyamide‐6,6 (PP–PA66), and two compatibilizers, N, N‐dihydroxyethyl monomaleic amide–grafted PP (g–PP) alone and together with a phenolic resin (PR), were investigated. Scanning electron microscopy (SEM) observations prove that the two compatibilizer systems are both effective for compatibilizing the blends, and the combined use of g–PP and PR is more effective than g–PP alone. Modulated‐temperature differential‐scanning calorimetry (M‐TDSC) determinations reveal that the ΔCp varies with the extent of compatibilization. For the uncompatibilized blends, the ΔCp for the PET component in PP–PET or for the PA66 component in PP–PA66 was found to be almost unchanged. After compatibilization these quantities become smaller. Also, the combined use of g–PP and PR results in the smallest ΔCp values for both blends. This ΔCp change with different compatibilizers is in very good agreement with the corresponding morphological variation observed by SEM. Thus, ΔCp can be taken as a new parameter for quantifying the extent of compatibilization, since it is a direct measure of interfacial content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2868–2876, 1999     

增容剂对PP/PET原位微纤化共混物的影响

通过"熔融挤出-热拉伸-淬冷"的方法制备了原位微纤化共混物。采用扫描电镜、差示扫描量热仪和力学性能测试等方法研究了增容剂PP-g-GMA含量对共混物微观形态、力学性能和结晶性能的影响。结果表明,增容剂的加入可明显提高两相相容性,改善界面效果,明显降低拉伸前初始粒子的尺寸,但同时使拉伸后形成的微纤呈现一定的损坏,长径比有所降低。增容剂可以明显改善微纤化共混物力学性能,当其含量为2 %（质量分数,下同）时拉伸强度比未增容试样提高了11.0 %,弯曲强度都提高了11.3 %;当其含量为6 %时冲击强度也比未增容共混物提高了34.5 %。此外,PET微纤对PP有很好的异相成核作用,使其结晶温度提高了16.3 ℃,结晶时间为纯PP的32 %左右,而增容剂的加入使共混物中PP的结晶时间延长。     

Role of reactive compatibilization in preparation of nanosilica/polypropylene composites

The effect of reactive compatibilization on the mechanical properties of nanosilica filled polypropylene (PP) composites was studied in this work. First, the nanoparticles were grafted with poly(glycidyl methacrylate) (PGMA) by solution free‐radical polymerization, and then melt blended together with PP matrix and aminated PP (PP‐g‐NH₂) that acts as reactive compatibilizer. The reaction between epoxide groups of the grafted PGMA on the nanoparticles and amine groups of PP‐g‐NH₂ during compounding greatly improved interfacial interaction in the composites. As a result, tensile strength, Young's modulus, and notch impact strength of PP composites were increased at rather low filler content. The experimental results indicated that the reinforcing and toughening effects were controlled by flexibility of the grafted polymer as well as processing methods. POLYM. ENG. SCI., 47:499–509, 2007. © 2007 Society of Plastics Engineers.     

In situ microfibrillar‐reinforced composites of isotactic polypropylene/recycled poly(ethylene terephthalate) system and effect of compatibilizer

Recycled poly(ethylene terephthalate) from waste bottles (hereafter, rPET) was used as an reinforcing material for isotactic polypropylene (iPP) based on the concept of in situ microfibrillar‐reinforced composites (iMFCs). Microfibers of rPET were successfully generated during melt‐extrusion and subsequent drawing and preserved in the final injection‐molded specimens. The effects of draw ratio, initial size of ground rPET flakes, and rPET content on morphological appearance of the extrudates and the as‐formed rPET fibers and mechanical properties of the as‐prepared iMFCs were investigated. The results showed that diameters of the as‐formed rPET fibers decreased with increasing draw ratio, and the initial size of ground rPET flakes did not affect the final diameters of the as‐formed rPET fibers nor the mechanical properties of the as‐prepared iMFCs. Flexural modulus, tensile modulus, and tensile strength of iPP/rPET iMFCs were improved by the presence of rPET microfibers and further improvement could be achieved by the addition of maleic anhydride‐grafted iPP (PP‐g‐MA), which was used as the compatibilizer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1173–1181, 2006     

Ultrasonic treatment of polypropylene,polyamide 6, and their blends

The mechanical and rheological properties of polypropylene (PP), polyamide 6 (PA6), and their blends treated by high‐intensity ultrasound during extrusion were investigated. A lower head pressure was achieved in the extrusion of these thermoplastics. The mechanochemical and sonochemical effects of ultrasound led to simultaneous ionic condensation reactions and degradation in a homogeneous melt of PA6, with a prevailing effect of enhanced polycondensation reactions. The observed improvements in the mechanical properties of ultrasonically treated PA6 were attributed to condensation reactions, which yield a higher molecular weight, a higher crystallinity, and a more uniform crystal size distribution. At high ultrasound amplitudes, for PP, the degradation of polymer chains was observed with little deterioration of the mechanical properties. For ultrasonically treated PP/PA6 blends, a competition between the degradation and partial in situ compatibilization effect was found. At certain blend ratios, the tensile toughness and impact strength of the treated blends were almost double those of the untreated blends. However, full compatibilization was not achieved, possibly because of the low coupling selectivity of highly reactive radicals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2643–2653, 2006     

Process–structure–property relationship in ternary short‐glass‐fiber/elastomer/polypropylene composites

Short‐glass‐fiber (SGF)‐reinforced polypropylene (PP) composites toughened with a styrene/ethylene butylene/styrene (SEBS) triblock copolymer were injection molded after extrusion. Furthermore, a maleic anhydride (MA)‐grafted SEBS copolymer (SEBS‐g‐MA) was used as an impact modifier and compatibilizer. The effects of the processing conditions and compatibilizer on the microstructure and tensile and impact performance of the hybrid composites were investigated. In the route 1 fabrication process, SGF, PP, and SEBS were blended in an extruder twice, and this was followed by injection molding. In route 2, or the sequential blending process, the elastomer and PP were mixed thoroughly before the addition of SGF. In other words, either PP and SEBS or PP and SEBS‐g‐MA pellets were premixed in an extruder. The produced pellets were then blended with SGF in the extruder, and this was followed by injection molding. The SGF/SEBS‐g‐MA/PP hybrid fabricated by the route 2 process exhibited the highest modulus, yield stress, tensile stress at break, Izod impact energy, and Charpy drop weight impact strength among the composites investigated. This was due to the formation of a homogeneous SEBS elastomeric interlayer at the SGF and matrix interface of the SGF/SEBS‐g‐MA/PP hybrid. This SEBS rubbery layer enhanced the interfacial bonding between SGF and the matrix of the SGF/SEBS‐g‐MA/PP hybrid. The correlations between the processing, microstructure, and properties of the hybrids were investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1384–1392, 2003