Molecular weight segregation induced by interfacial melt reactivity in polyamide 6/reactive rubber blends

Polyamide 6 (PA) and ethylene-propylene rubber with maleic functionality (EPMA) were blended in a batch mixer. EPMA anhydride groups react with amine chain ends of polyamide and form a grafted copolymer at the interface. The molecular weights of the grafted PA and of the free PA were measured. The molecular weight of the free PA decreases during the processing. This effect is due to the hydrolysis of the PA consecutively to its reaction with anhydride groups. The molecular weight of both grafted and free polyamide decreases during the processing. Moreover, the molecular weight of the grafted PA is lower than that of the free PA. At constant mixing time, a high conversion level produces grafted PA with a higher molecular weight. This is the result of molecular weight segregation for interfacial reaction. Small molecules react faster at the interface than larger ones. If we compare experimental results with model predictions, two segregation regimes are observed. For high shear and low EPMA concentrations, dispersion is very fast; the segregation only depends on molecular elasticity. In this case, the best correlation between model and experiment is obtained for low interfacial thicknesses. For low shear, or for EPMA concentrations close to the phase inversion composition, the segregation is more noticeable, which is mainly due to the diffusion of macromolecules through the brush of already grafted molecules. In this case, there is a clear competition between the compatibilization and the grafting reaction. Molecular weight segregation gives low ratio of the grafted PA molecular weight to the free PA molecular weight. This is detrimental to interfacial properties of the grafted copolymer formed by melt reactivity. Strategies are developed to improve this ratio in order to investigate its influence on the mechanical properties. © 1995 John Wiley & Sons, Inc.     

Graft formation and chain scission in blends of polyamide-6 and -6.6 with maleic anhydride containing polymers

The in situ formation of a compatibilizer, consisting of a copolymer of PA grafted onto a maleic anhydride (MA) containing polymer, is essential for the morphology and properties of the corresponding PA blends. In this study four blends, containing PA-6 or PA-6.6 and EPDM-g-MA or poly(styrene-co-maleic anhydride) (SMA; 28 wt % MA), were prepared and characterized. Chemical analyses showed that the amount of PA graft is independent of the blend composition. Going from EPDM-g-MA to SMA the MA content of the original MA-containing polymer increases, which in the corresponding blends results in an increase in the number of PA grafts and a decrease in the length of the PA grafts. In the SMA blends the number averaged molecular weight of the grafted PA is only about 200 g/mol. It is postulated that the water molecule, released upon imide formation at the PA/(MA-containing polymer) interface, hydrolyses a PA amide group, resulting in a new amine end group, which in its turn reacts with the MA-containing polymer, etc. Differential scanning calorimetry shows that the degree of crystallinity of the PA phase is decreased only when the size of the PA phase between the MA-containing polymer domains approaches the PA crystalline lamellar thickness. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 179–188, 1998     

Influence of an interfacial agent on the structure of polypropylene-polyamide fibres

In this paper the structure and properties of fibres prepared from the polypropylene/polyamide (PP/PA6) blend have been studied as a function of the interfacial-agent (IFA) content. For this purpose the grafted polypropylene-maleic anhydride copolymer was used. Fibres containing 20% of PA6 and 80% of PP possess the phase matrix-fibril structure. The size and distribution of fibres in the dispersed PA6 phase in the PP matrix depend on the interfacial-agent amount. Due to the indirect nucleating effect the PA6 phase has been found to act, in the presence of the interfacial agent, on the PP crystallization during fibre formation. As a result, undrawn fibres have the more pre-oriented and crystalline PP matrix with the morphological rod-like structure. The pre-orientation of the dispersed fibrilar PA6 phase is minimum. Mechanical properties of the drawn blended fibres are favourably influenced provided that the interfacial-agent concentration is higher than 1%. The growing rate of the mutual interaction between the components was mostly reflected in the increased values of Young's modulus.     

A study on melt grafting of maleic anhydride onto low‐density polyethylene and its blend with polyamide 6

Graft copolymerization of low‐density polyethylene (LDPE) with a maleic anhydride (MAH) was performed using intermeshing corotating twin‐screw extruder in the presence of benzoyl peroxide (BPO). The LDPE/polyamide 6 (PA6) and LDPE‐g‐MAH/PA6 blends were prepared in a corotating twin‐screw extruder. The melt viscosity of the grafted LDPE was measured by a capillary rheometer. The grafted copolymer was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microcopy (SEM). The influence of the variation in temperature, BPO and MAH concentration, and temperature on the grafting degree and on the melt viscosity was studied. The grafting degree increased appreciably up to about 0.45 phr and then decreased continuously with an increasing BPO concentration. According to the FTIR analysis, it was found that the amount of grafted MAH on the LDPE chains was ～5.1%. Thermal analysis showed that melting temperature of the graft copolymers decreases with increasing grafting degree. In addition to this, loss modulus (E″) of the copolymers first increased little with increasing grafting and then obviously decreased with increasing grafting degree. Furthermore, the results revealed that the tensile strength of the blends increased linearly with increasing PA6 content. The results of SEM and mechanical test showed that the blends have good interfacial adhesion and good stability of the phase structure, which is reflected in the mechanical properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 267–275, 2010     

Effect of maleic anhydride‐grafted polytetrafluoroethylene on the tensile and tribological properties of blending polytetrafluoroethylene with polyamide‐6

Blending polytetrafluoroethylene (PTFE) to polyamide‐6 (PA6) with and without maleic anhydride‐grafted polytetrafluoroethylene (PTFE‐g‐MA) was produced in a corotating twin screw extruder, where PTFE acts as the polymer matrix and PA6 as the dispersed phase. The effect of PTFE‐g‐MA on the tensile properties and tribological propertiesof PTFE/PA6 polymer blends is studied. Results show that the structural stability and morphology of the blends were greatly improved by PTFE‐g‐PA6 grafted copolymers, which were formed by the in situ reaction of anhydride groups with the amino end groups of PA6 during reactive extrusion forming an imidic linkage. The presence of PTFE‐g‐PA6 in the PTFE continuous phase improves the interfacial adhesion, as a result of the creation of an interphase that was formed by the interaction between the formed PTFE‐g‐PA6 copolymer in situ and both phases. Compared with thePTFE/PA6 without PTFE‐g‐MA, the PTFE/PA6 with PTFE‐g‐MAhad the lowest friction coefficient and wear under given applied load and reciprocating sliding frequency. The interfacial compatibility of the composite prevented the rubbing‐off of PA6, accordingly improved the friction and wear properties of the composite. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of SEBS-g-BTAI on the morphology, structure and mechanical properties of PA6/SEBS blends

Styrene-b-(ethylene-co-1-butene)-b-styrene (SEBS) triblock copolymer functionalized with ε-caprolactam blocked allyl (3-isocyanate-4-tolyl) carbamate (SEBS-g-BTAI) was used to toughen polyamide 6 (PA6) via reactive blending. Compared to the PA6/SEBS blends, mechanical properties such as tensile strength, Young’s modulus, especially Izod notched strength of PA6/SEBS-g-BTAI blends were improved distinctly. Both rheological and FTIR results indicated a new copolymer formed by the reaction of end groups of PA6 and isocyanate group regenerated in the backbone of SEBS-g-BTAI. Smaller dispersed particle sizes with narrower distribution were found in PA6/SEBS-g-BTAI blends, via field emitted scanning electron microscopy (FESEM). The core-shell structures with PS core and PEB shell were also observed in the PA6/SEBS-g-BTAI blends via transmission electron microscopy (TEM), which might improve the toughening ability of the rubber particles.     

The effect of in situ-formed copolymers on the morphology of reactive poly(phenylene ether)/poly(amide-6) blends

Poly(phenylene ether) (PPE)/poly(amide-6) (PA6) blends are examined in light of the information provided by two-dimensional chromatography and chemorheology. Chromatography provides a snapshot of the blend composition in the finished material, while rheology presents us with a direct insight into the reactions taking place in the melt. Block copolymer formation is chromatographically confirmed for the blends prepared with a coupling agent, but also for the blend prepared without any coupling agent. No co-continuous morphology is observed by scanning electron microscope. Instead, a coarse structure of PPE droplets in the PA6 matrix is obtained for the blend prepared without coupling agent. This is explained by the combined effects of the low viscosity of PA6 and the inherently formed copolymers. The PPE domains are smaller in the blends prepared with the coupling agents. Their size is correlated with the copolymer formation, surface tension, and interphase relaxation time. The data evidence a complex system where reactions resulting in the formation of copolymer via coupling or grafting take place together with the extension of the PPE and condensation growth of the PA6 polymers.     

Influence of hyperbranched polymers on the interfacial tension of polypropylene/polyamide‐6 blends

The compatibilizing effect of polypropylene (PP) grafted with hyperbranched polymers (PP–HBP) has been investigated in PP/polyamide‐6 (PA‐6) blends. Because of its high reactivity and diffusitivity, PP–HBP has been shown to be a more effective compatibilizer in decreasing the interfacial tension than the commonly used maleic anhydride–grafted polypropylene (PP–MAH). This article describes the influence of PP–HBP and PP–MAH on the interfacial tension between PP and PA‐6, as measured by the deformed drop‐retraction method (DDRM). Overall, PP–HBP yielded lower interfacial tension values between PP and PA‐6, which resulted in a finer particle size of the secondary phase. The time dependence of the interfacial tension can be monitored by DDRM, enabling evaluation of the diffusitivity and reactivity of the compatibilizer. A model based on particle coarsening has been developed to describe the time dependence of the interfacial tension. This model showed that the diffusitivity and reactivity for PP–HBP was higher than that of PP–MAH. Therefore, PP–HBP has strong potential as a compatibilizer in diffusitivity‐dependant processes such as film coextrusion and fusion bonding. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2069–2077, 1999     

Blends of bisphenol-A polycarbonate and acrylic polymers: II. PC/acrylic copolymers as a new route for compatibilization

An acrylic polymer containing acid and anhydride units, referred to as reactive polyglutarimide (RPGI), has been used to react with PC. The reaction has been previously determined as an acidolysis of the carbonate bond which breaks the PC chain in two parts. One of those two parts remains free while the other one is grafted on the acrylic backbone. We have found that the anhydride units could also react with the carbonate bonds. In this case the PC macromolecule would also be broken in two parts, which would, however, both be grafted on the acrylic backbone. The reaction has been performed in solution in order to keep good contact between the reacting units. The influence of temperature and concentration on the grafting ratio has been studied. The best experimental conditions were determined in order to obtain a grafted copolymer where the acrylic backbone only supports, on the average, one PC side chain through acid reaction or two PC chains through anhydride reaction. Indeed, these two types of reactions could not be isolated. The efficiency of this copolymer as emulsifier has been studied in solution cast blends as well as in melt mixed blends. The copolymer strongly affects the microstructure in solution cast blends where films containing 30 wt % of PC have become transparent. However, the dispersed phase size of solvent cast blends could be highly influenced by the casting conditions related to solvent trapping. In melt mixed samples, the copolymer also reduces significantly the dispersed phase size, but no transparent blends have been observed so far. These results were compared with those given in the literature describing the efficiency of a synthesized copolymer which has a more complicated structure. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 735–747, 1997     

A new method for preparation of PS‐g‐PA6 grafted copolymer micelles

This work described a new method for the synthesis of PS‐g‐PA6 grafted copolymer micelles. PS‐g‐PA6 sphere micelles were synthesized by using a same solvent at the absence of selective solvent. The morphologies of micelles were characterized by SEM and TEM. The PS‐g‐PA6 micelles loaded Fe₃O₄ particles have better MRI imaging effect. The synthesis strategy developed here may present a desirable way to fabricate grafted copolymer micelles.     

Improving the flame retardancy of polyamide 6 by incorporating hexachlorocyclotriphosphazene modified MWNT

A nitrogen‐, phosphorus‐ and chlorine‐containing flame retardant, hexachlorocyclotriphosphazene (HCTP), has been covalently grafted onto the surface of multi‐wall carbon nanotubes (MWNT) to obtain MWNT‐HCTP. Polyamide 6 (PA6)/MWNT composites were then prepared via melt compounding. The flammability of PA6/MWNT composite was characterized by cone calorimetry, limiting oxygen index (LOI) and UL‐94 tests. The results showed that peak heat release rate of samples containing 3 wt% MWNT‐HCTP was only 460 kW/m², which decreased by 35.2% compared with that of a neat PA6 sample. The LOI value was increased from 22.7% to 26.5%, and UL‐94 test performance was also significantly improved by the presence of MWNT‐HCTP. Scanning electron microscope (SEM) and optical microscope analysis showed that modified MWNT had a better dispersion and compatibility in PA6 than unmodified MWNT. The composition of residue chars and volatile products was investigated by SEM/energy dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric‐FTIR, respectively. It was proposed that grafted HCTP was mainly functioned in the condensed phase, where P, N can synergistically promote char formation and Cl element can catch free radicals to terminate the chain reaction during combustion of the PA6 composite. Copyright © 2014 John Wiley & Sons, Ltd.     

Grafting of polyamide 6 by the anionic polymerization of ε‐caprolactam from an isocyanate bearing polystyrene backbone

The grafting of polyamide 6 (PA6) onto polystyrene (PS) can rely on the use of a copolymer of styrene (St) and 3‐isopropenyl‐α, α‐dimethylbenzene isocyanate (TMI), PS‐co‐TMI, to activate the polymerization of ε‐caprolactam (CL) in the presence of sodium ε‐caprolactam (NaCL) as an anionic catalyst. This article is aimed at answering the following key questions. First, do all the isocyanate moieties of the PS‐co‐TMI participate in the activation of the polymerization of CL? Second, what are the composition of the resulting polymer product and the structure of the resulting graft copolymer? The results show that the isocyanate moieties had all participated in the activation of the polymerization, implying that each isocyanate moiety has led to the formation of a PA6 graft. The as‐polymerized product was composed of a pure PS‐g‐PA6 graft copolymer, homo‐PA6, and unreacted CL. Moreover, when the composition of a PS‐co‐TMI/CL/NaCL system was fixed, the mass ratio between the PA6 grafts and PS backbone of the pure PS‐g‐PA6 graft copolymer was almost a constant and was almost independent of its molar mass. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4766–4776, 2008     

Reinforcement of solid‐melt interfaces for semicrystalline polymers in a sequential two‐staged injection molding process

The solid‐melt interfaces between polyethylene (PE) and polyamide 6 (PA6) reinforced by in situ reactive compatibilization in a sequential two‐staged injection molding process has been studied in this work. The effects of the maleic anhydride grafted PE content and processing parameters, such as injection pressure, injection speed, melt temperature, and mold temperature, on the interfacial adhesion were investigated experimentally. The results of the interfacial adhesion characterized by lap shear measurement showed that the interfacial temperature and heat transfer between PE and PA6 interfaces play a very significant role in the bonding process. The fracture surfaces of the specimens prepared at different calculated interfacial temperature were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), which suggested that the fracture failure changes from adhesive to cohesive failure with increasing interfacial temperature. The contribution of crystalline parts of the in situ formed copolymers to the enhancement in interfacial adhesion also was determined by DSC analysis. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1112–1124, 2009     

From incompatible poly(aryl ether sulfone)/polyamide 4.6. blends to new impact resistant alloys by a synergistic combination of a block copolymer emulsifier and an impact modifier

The compatibilization and impact modification of blends of a relatively new engineering plastic polyamide 4.6 (PA 4.6) and a poly(aryl ether sulfone) (PSU) are investigated. PSU-b-PA6 block copolymers, which can be easily synthesized by ring opening polymerization of ϵ-caprolactam in the presence of a commercial PSU, were found to be very efficient emulsifiers for these incompatible blends. Small amounts (1–4%) of copolymer are sufficient to significantly reduce the particle size and to improve the tensile and impact properties. Combinations of the copolymer and an impact modifier (ethylene-propylene rubber grafted with maleic anhydride) are synergistic and high impact PSU/PA 4.6 alloys are obtained in that way.     

Effect of Structure of Functionalizing Molecules on the Inter‐Macromolecular Reactions and Blending of Poly(ethylene‐co‐propylene) (EPM) with Poly(6‐aminohexanoic Acid) (PA6)

Two different functionalizing systems, i.e., monohexadecyl maleate (= hexadecyl hydrogen (2Z)‐but‐2‐enedioate) in the presence of dicumyl peroxide (= bis(1‐methyl‐1‐phenylethyl) peroxide) or 4‐carboxybenzenesulfonazide (= 4‐(azidosulfonyl)benzoic acid), were used in distinct experiments to perform in a one‐step procedure the formation of a EPM–PA6 graft copolymer, necessary to obtain a compatibilized blend, from a molten mixture of ethylene–propylene copolymer (EPM) and polyamide 6 (PA6). The characterization of the graft polymer by selective solvent extraction of the blends and the subsequent IR and NMR analysis of the various fractions established the occurrence of functionalization reactions preferentially onto the polyolefin with both reagents. Also the formation in good yield of graft copolymers at the phases interface was observed. Moreover, the morphology and thermal characterizations of the blends by means of SEM and DSC analyses were used to evaluate the compatibilization extent in comparison with blends obtained by the conventional two‐step procedure or by the one‐step procedure with commercial maleic acid derivatives.     

Reactive blending of PE‐GMA/PA6 effect of composition and processing conditions

Blends of ethylene‐glycidyl methacrylate copolymer (PE‐GMA) and polyamide 6 (PA6) were prepared in a corotating twin screw extruder. Two processing temperatures were used in order to disperse PA6 in two forms: at high temperature in the molten state in molted PE‐GMA Matrix (emulsion type mixture) and at lower temperature as fillers in molted PEGMA matrix (suspension type mixture). Processed blends were analyzed by scanning electron microscopy and dynamic mechanical experiments to probe the reactivity in the extruder and the compatibilization phenomena. The dependence of the morphology and the rheological properties of PE‐GMA/PA6 blends on blend composition and screw rotational speed was also investigated and is discussed in the paper. The results show that dispersion of the two polymers in the molten state leads to a higher level of interfacial reaction. They also show that whatever the screw rotational speed and the temperature of extrusion are, the rate of interfacial reaction in PE‐GMA/PA6 blends is higher for 50/50 PE‐GMA/PA blends than for 70/30 PE‐GMA/PA blends. Copyright © 2015 John Wiley & Sons, Ltd.     

Reactive blending: inhomogeneous interface grafting in melts of maleinated polystyrene and polyamides

To be competitive, most blends need compatibilizers, usually copolymers with a blocky architecture, the chains of which cover the interfaces between the blend phases, refining the phase morphology and improving the interface strength. When the blend components are suitably functionalized, such copolymers can be conveniently generated in situ, in processes of reactive blending. Normally, graft copolymers are created. The polymer–polymer coupling proceeds exclusively in the interfaces. This interface grafting is (i) pivotal in the design of modern blend systems and (ii) an interesting route towards novel copolymers. The complex kinetics of interface grafting in blend melts have so far attracted little attention. In a model study, amino terminated polyamide 12 (PA) was grafted in the melt onto heavily maleinated polystyrene (SMA; S: styrene and MA: maleic anhydride). Anhydride and amino functions react at high temperatures fast and irreversibly by imide condensation. A series of SMA/PA blends differing in composition and PA chain lengths was investigated, with the aim of driving the grafting to high conversions so a pure graft copolymer SMAgPA would result, instead of an SMA/PA/SMAgPA blend. However, a pure copolymer was never obtained. The grafting remained incomplete, except with very short-chained PA and only at equal weight fractions of SMA and PA. More importantly, the SMA chains were never grafted evenly. Instead, “overgrafted” and “undergrafted” chains SMAgPA coexisted in one and the same product. It appears that the SMAgPA chains form an auto-inhibitory barrier in the interfaces that prevents random grafting. Grafting proceeds to high conversion only in SMA/PA blends with a co-continuous phase morphology where the interfaces are constantly torn apart and renewed, during melt blending, so the reaction is constantly reactivated. © 1998 John Wiley & Sons, Ltd.     

Reactive compatibilization of polyamide‐6 (PA 6)/polybutylene terephthalate (PBT) blends by a multifunctional epoxy resin

A multifunctional epoxy resin has been demonstrated to be an efficient reactive compatibilizer for the incompatible and immiscible blends of polyamide‐6 (PA 6) and polybutylene terephthalate (PBT). The torque measurements give indirect evidence that the reaction between PA and PBT with epoxy has an opportunity to produce an in situ formed copolymer, which can be as an effective compatibilizer to reduce and suppress the size of the disperse phase, and to greatly enhance mechanical properties of PA/PBT blends. The mechanical property improvement is more pronounced in the PA‐rich blends than that in the PBT‐rich blends. The fracture behavior of the blend with less than 0.3 phr compatibilizer is governed by a particle pullout mechanism, whereas shear yielding is dominant in the fracture behavior of the blend with more than 0.3 phr compatibilizer. As the melt and crystallization temperatures of the base polymers are so close, either PA or PBT can be regarded as a mutual nucleating agent to enhance the crystallization on the other component. The presence of compatibilizer and in situ formed copolymer in the compatibilized blends tends to interfere with the crystallization of the base polymers in various blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 23–33, 2000     

HDPE/PA6反应增容体系的形态演化与黏弹行为

采用扫描电子显微镜(SEM)与先进流变扩展系统(ARES),研究了马来酸酐接枝高密度聚乙烯(HDPE-g-MAH)对高密度聚乙烯/尼龙6(HDPE/PA6)共混体系形态结构和黏弹行为的影响.发现HDPE-g-MAH的加入可原位生成尼龙6-高密度聚乙烯接枝共聚物(HDPE-g-PA6),使基体与分散相间的相容性显著改善,且随其添加量的增加两者相容性更好,导致HDPE/PA6体系形态结构变化.研究结果表明,由ARES获得的体系黏弹行为参数随HDPE-g-MAH含量的变化可与由SEM所观察到的微观形貌演化很好关联,动态流变学方法可敏感表征增容剂的加入所引起的HDPE/PA6界面性质变化,且能够反映分子链间相互作用的变化及由此导致的分散相颗粒网络的形成.     

Grafting of 4‐Vinyl Pyridine onto Nylon‐6 Initiated by Cu(III)

In this article, the graft copolymerization of 4‐vinyl pyridine (4VP) onto nylon‐6 (PA6) using potassium diperiodacuprate (III) (DPC)–PA6 redox system as initiator is investigated in an alkaline medium. The structure and the properties of graft copolymer are confirmed by Fourier transfer infrared spectroscopy (IR), X‐ray diffraction and thermogravimetric analysis (TGA). The mechanism is proposed to explain the generation of radicals and the initiation. The effects of reaction variables, such as the initiator concentration, ratio of 4VP to PA6, pH, as well as reaction temperature and time are investigated. Graft copolymers with high grafting efficiency (>95%) were obtained, which indicated that the DPC–PA6 redox system was an efficient initiator for this graft copolymerization. The quaternized PA6‐g‐P4VP (QPAVP) is proven to be an excellent adsorbent to heavy metal ions.