Chain extension of polyamide 6/organoclay nanocomposites

Thermal degradation of polyamide 6 (PA6)/organoclay nanocomposites is a serious impediment to wider applications of these nanocomposites. In this study, a solution is proposed based on the well‐established use of chain extenders. As in PA6, thermal degradation, in the absence of moisture, produces broken polymer chains with amide end groups, a chain extender with anhydride functionalities, known to be strongly reactive with amide groups, was used to reconnect the chains. Experiments conducted using a laboratory twin‐screw extruder were first checked, through transmission electron microscopy observations, to have produced good organoclay intercalation and exfoliation into PA6. Following from this, samples with the chain extender added were produced and characterized. The data obtained were conclusive in the effectiveness of the chain extender: for the chain extended nanocomposites, there is an enhancement in the value of the complex viscosity by 7 times and in the storage modulus by 88 times, while the tensile modulus increased by 57% compared with the neat PA6. The nonchain extended nanocomposite achieved in comparison an enhancement of 2 times the value of the complex viscosity and 19 times the storage modulus while the tensile modulus increased by 53% compared to the neat PA6. These data provide conclusive proof on the rationale that anhydride functionalities should be sought when developing chain extenders for PA6 nanocomposites. POLYM. ENG. SCI., 59:1233–1241 2019. © 2019 Society of Plastics Engineers     

Chain extension of recycled PA6

Recycling of polymers is a necessity in our intensively consuming polymer world but the nature of polymers is such that they are prone to thermal degradation when re‐extruded and this poses technical challenges to recycling. This article describes research that seeks to rebuild the structure of degraded PA6. We present data from controlled experiments with pristine pPA6 extruded to form a base recycle rPA6 to which we added two chain extenders, separately: one with anhydride multifunctionality (ANHY), highly reactive with amide groups and one with epoxy multifunctionality (EPOX), less reactive. We found from rheological data carried out in the linear viscoelastic region (so as to study structural changes) a striking difference in the ability of the chain extenders to rebuild structure: 306% increase in the complex viscosity of rPA6/ANHY compared to 25% in that of rPA6/EPOX of the base rPA6. Mechanical and thermal (DSC and TGA) tests confirmed the superior efficacy of the multifunctional anhydride chain extender. Beside the practical benefit that ensues from this research, it also provides a strategic platform to develop chain extenders for other degrading polymers on the basis of understanding the degradation chemical reaction and targeting the most reactive end group of the split chains. POLYM. ENG. SCI., 58:1037–1042, 2018. © 2017 Society of Plastics Engineers     

Polyurethane elastomers with amide chain extenders of uniform length

Toluene diisocyanate based polyurethanes with amide extenders were synthesized poly(propylene oxide) with a number average molecular weight of 2000 and endcapped with toluene diisocyanate was used as the polyether segment. The chain extenders were based on poly(hexamethylene terephthalamide): hexamethylene diamine, bisamine-diamide and bisamine-tetra-amide. The linear poly(ether bisurethane-bisurea-amide)s (PUA) were colorless transparent thermoplastic elastomers with a high molecular weight. The polymers were analyzed by IR and DSC, the morphology studied by TEM, the mechanical properties studied by DMTA and the tensile, the elastic properties by compression and tensile set and thermal stability by melt rheology.The phase separation with these amide extenders was by crystallization. Increasing the length of the amide chain extender increased the modulus and the melting temperature of the PUA without changing the good low temperature properties. Also the elastic properties improved with amide segment length. The fracture stress increases with amide extender length. At 200 °C, the melt stability of the PUA with the bisamine-diamide chain extender was good.     

脂环族环氧树脂扩链PA 1010

以脂环族环氧树脂为扩链剂,对聚酰胺(PA)1010的加成型化学扩链做了研究,并对3种扩链剂(ZH9221、ZH206和TDE85)的偶联效果和扩链产物的热稳定性能进行了探讨。结果表明,3种扩链剂对PA1010的扩链增粘均十分有效．熔体转矩可分别达到初始值的4倍、5倍和6倍以上,而且所需反应时间依次减少。其中,TDE85由于带有2个缩水甘油酯型环氧基团而活性很高,但在一定温度下熔体转矩达到极大值后开始缓慢下降,表明扩链产物在高温条件下发生断链。扩链剂用量存在最佳值．用量过多对扩链反应并无益处。扩链后PA1010的端羧基含量降至原先的20％～30％。     

Effects of addition of functionalized SEBS on rheological,mechanical, and tribological properties of polyamide 6 nanocomposites

The effects of the addition of styrene‐ethylene/butylene‐styrene copolymer (SEBS) with various functionalized groups on the rheological, mechanical, and tribological properties on polyamide 6 nanocomposite filled with layered silicate (PA6/Clay) were investigated. Four types of SEBS: unmodified SEBS (SEBS), maleic anhydride grafted SEBS (SEBS‐g‐MA), amine group grafted SEBS (SEBS‐g‐NH₂), and carboxyl group grafted SEBS (SEBS‐g‐COOH) were added with PA6/Clay nanocomposite to prepare various polymer blends. These polymer blends were extruded by a twin screw extruder and injection molded. Dynamic viscoelastic properties of these blends in the molten state and their tensile, impact, and tribological properties were evaluated. The viscoelastic properties were found to increase with the addition of SEBS and were highly influenced by the types of functionalized groups contained. Influence of the addition of SEBS on the mechanical properties of these systems differed for each mechanical property. Although the tensile properties decreased with SEBS, Izod impact properties improved with the addition of various functionalized SEBS. These mechanical properties and viscoelastic properties correlated closely with the size of dispersed SEBS particles and interparticle distance. The tribological properties also improved with the addition of SEBS, and the influence of the amount added was higher than the type of SEBS used. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Characterization of low molecular weight carboxyl-terminated polyamides obtained by reactive extrusion of polyamide 6 with trimellitic anhydride

Reactive extrusion has been applied as a very effective and fast process for controlled chemical degradation of a commercial polyamide 6 with trimellitic anhydride in the melt. A reaction mechanism based mainly on the amide/anhydride reaction has been discussed and confirmed by measurements of the solution viscosity, end group analysis, SEC, NMR, and IR spectroscopy. The systematic loss of molecular weight of the polyamides resulting from PA chain repture and the formation of imide linkages and carboxyl end groups were investigated. The theoretical values of molecular weight and end group concentration of the obtained oligoamides predicted by the reaction mechanism are in good agreement with the experimental ones. © 1996 John Wiley & Sons, Inc.     

Studying the effects of chain extenders chemical structures on the adhesion and mechanical properties of a polyurethane adhesive

Chain extenders including diethanol amine (DEA) and 2-cyano-N,N-bis-hydroxyethyl acetamide (CNBA) were utilized to enhance the adhesion and mechanical properties of a polyurethane (PU) adhesive. The adhesion and mechanical properties of the adhesives were studied by peel test, tensile test and dynamic thermal analysis (DMTA) respectively. Results revealed that both chain extenders (DEA and CNBA) increased peel test modulus. The cross-linking density and toughness of the adhesive were significantly increased using chain extenders. Results showed that chain extender without side chain (DEA) could improve the adhesion and mechanical properties of the adhesive greater than chain extender with aliphatic side group (CNBA).     

尼龙6化学扩链

用挤出机熔融共混法,以双２口恶唑啉和双酰基双内酰胺化合物为扩链剂,对ＰＡ６进行化学扩链,使ＰＡ６的分子量由１６．７ｋｇ／ｍｏｌ提高到２１．０ｋｇ／ｍｏｌ,偶联效率最高可达７０％;同时考查了扩链剂用量、铜盐、共混温度与时间以及后热处理对扩链效果的影响。     

PETG连续挤出发泡行为

采用环氧型扩链剂对苯二甲酸-乙二醇-1,4-环己烷二甲醇共聚酯(PETG)进行熔融扩链,并利用高级扩展流变仪、熔体强度测定仪和扫描电子显微镜分别进行了剪切流变、拉伸流变测试和连续挤出发泡行为研究。结果表明:扩链后PETG的储能模量、损耗模量、复数黏度随扩链剂含量的增加而增大,而其损耗因子随扩链剂含量的增加而减小;扩链剂的加入能有效提高PETG树脂的熔体强度和改善其"可发泡性",在发泡成型过程中可以有效阻止泡孔的塌陷和破裂,进而形成泡孔尺寸和形态分布较为均匀的制品。     

Synthesis and properties of waterborne polyurethane adhesives: effect of chain extender of ethylene diamine,butanediol, and fluoro-butanediol

Waterborne polyurethane (WBPU) adhesives were prepared using poly(tetramethylene oxide glycol), 4,4’-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrophilic agent dimethylol propionic acid and chain extender of 2,2,3,3-tetrafluoro-1,4-butanediol (TFBD), ethylene diamine (EDA), and 1,4-butanediol. All three chain extenders have been used as single and mixed (different ratio) content during synthesis, and the effect of chain extender and their content to the properties of tensile strength, Young’s modulus, water swelling (%), and adhesive strength was investigated. The adhesive strength value was higher using EDA as a single-chain extender; however, the potentiality of adhesive strength under water was improved using mixed-chain extenders of EDA and TFBD in WBPU adhesives. The maxima potentiality was observed with 6.31 mole% TFBD and 2.10 mole% EDA in WBPU adhesives.     

Reactive blending of poly (dimethylsiloxane) with nylon 6 and poly (styrene):Effect of reactivity on morphology

Reactive compatibilization was used to control and stabilize 20–30wt% poly(dimethylsioxane) (PDMS) dispersions in nylon 6 (PA) and poly(styrene) (PS), respectively. The effect of the type of reation (amine (NH₂)/anhydride (An), NH₂/ epoxy(E) and carboxylic acid (COOH)/E) on the morphology was studied with electron microscopy. PS and PDMS have mutual solvents thus it was possible to use gel permeation chromatography (GPC) to determine the concentration of block copolymer in PS/PDMS blends. Reactive blending of PA6 with difunctional PDMS‐(AN)₂ did not decrease the PDMS particle size compared to the non‐reactive blend (～10μm). Particle size decreaeased significantly to about 0.5 μm when PA6 was blended with a PDMS containing about 4 random An groups along the chain. For the PS/PDMS blends, GPC revealed that the NH₂/An reaction formed about 3% block copolymer and produced stable PDMS particles ～ 0.4 μm. No reaction was detected for the PS‐NH₂/PDMS‐E blend and the morphology was coarse and unstable. Also, PS‐NH₂/PDMS‐An reactivity was lower compared to other systems such as PS/ poly (isoprene) and PS/poly(methaacrylte) using the same reaction. This was attributed to the relatively thinner PS/PDMS interface dueto the high PS/PDMs immiscibility.     

Chain extension of recycled poly(ethylene terephthalate) with 2,2′‐(1,4‐phenylene)bis(2‐oxazoline)

The present work provides improved recycled high molecular weight poly(ethylene terephthalate) (PET) by chain extension using 2,2′‐(1,4‐phenylene)bis(2‐oxazoline) (PBO) as the chain extender. PBO is a very reactive compound toward macromolecules containing carboxyl end groups but not hydroxyl end groups. In the case of PET, where both species are present, for even better results, phthalic anhydride (PA) was added in the initial sample, before the addition of PBO. With this technique, we succeeded in increasing the carboxyl groups by reacting PA with the hydroxyl terminals of the starting polymer. From this modification of the initial PET sample, PBO was proved an even more effective chain extender. So, starting from a recycled PET with intrinsic viscosity [η] = 0.78, which would be [η] = 0.69 after the aforementioned treatment without a chain extender or M̄_n = 19,800, we prepared a PET grade having [η] = 0.85 or M̄_n = 25,600 within about 5 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2206–2211, 2000     

Effect of chain extender structure on the properties and morphology of polyurethanes based on H12MDI and mixed macrodiols (PDMS–PHMO)

The effect of chain extender structure on properties and morphology of α,ω‐bis(6‐hydroxyethoxypropyl) polydimethylsiloxane (PDMS) and poly(hexamethylene oxide) (PHMO) mixed macrodiol‐based aliphatic polyurethane elastomers was investigated using tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). All polyurethanes were based on 50 wt % of hard segment derived from 4,4′‐methylenecyclohexyl diisocyanate (H₁₂MDI) and a chain extender mixture. 1,4‐Butanediol was the primary chain extender, while one of 1,3‐bis(4‐hydroxybutyl)tetramethyldisiloxane (BHTD), 1,3‐bis(3‐hydroxypropyl)tetramethyldisiloxane (BPTD), hydroquinonebis(2‐hydroxyethyl)ether (HQHE), 1,3‐bis(3‐hydroxypropyl)tetramethyldisilylethylene (HTDE), or 2,2,3,3,4,4‐hexafluoro‐1,5‐pentanediol (HFPD) each was used as a secondary chain extender. Two series of polyurethanes containing 80 : 20 (Series A) and 60 : 40 (Series B) molar ratios of primary and secondary chain extenders were prepared using one‐step bulk polymerization. All polyurethanes were clear and transparent and had number‐average molecular weights between 56,000 and 122,100. Incorporation of the secondary chain extender resulted in polyurethanes with low flexural modulus and high elongation. Good ultimate tensile strength was achieved in most cases. DSC and DMTA analyses showed that the incorporation of a secondary chain extender disrupted the hard segment order in all cases. The highest disruption was observed with HFPD, while the silicon‐based chain extenders gave less disruption, particularly in Series A. Further, the silicon chain extenders improved the compatibility of the PDMS soft segment phase with the hard segment, whereas with HFPD and HQHE, this was not observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2979–2989, 1999     

Effect of Two‐Step Chain Extension using Joncryl and PMDA on the Rheological Properties of Poly (lactic acid)

This research considers a two‐step chain extension reaction in the presence of two chain extenders, Joncryl and Pyromellitic dianhydride (PMDA), as a solution for poor melt properties of poly (lactic acid) (PLA). The aim of adding PMDA is to increase the carboxyl groups via the anhydride ring‐opening reaction so that the reaction between PLA and Joncryl could be facilitated since the reactivity between the epoxy and carboxyl group is more than epoxy and hydroxyl group. The reactions are confirmed by measuring the acid value, and a two‐step reaction mechanism is suggested. Shear and elongational rheological properties of the samples are investigated; furthermore, gel permeation chromatography analyses and tensile tests are exploited for studying the molecular weight and tensile properties, respectively. The results show that the chain extension reactions lead to an increase in the storage modulus, complex viscosity, and molecular weight. Also, the PLA chains which are extended utilizing both chain extenders simultaneously evince a synergistic improvement in the shear and elongational rheological properties due to longer segments between branching points on the structure.     

Preparation and characterization of high melt strength polypropylene with long chain branched structure by the reactive extrusion process

The reactive extrusion of maleic anhydride grafted polypropylene (PP‐g‐MAH) with ethylenediamine (EDA) as coupling agent is carried out in a corotating twin‐screw extruder to produce long chain branched polypropylene (LCBPP). Part of PP‐g‐MAH is replaced by maleic anhydride grafted high‐density polyethylene (HDPE‐g‐MAH) or linear low‐density polyethylene (LLDPE‐g‐MAH) to obtain hybrid long chain branched (LCB) polyolefins. Compared with the PP‐g‐MAH, PE‐g‐MAH, and their blends, the LCB polyolefins exhibit excellent dynamic shear and transient extensional rheological characteristics such as increased dynamic modulus, higher low‐frequency complex viscosity, broader relaxation spectra, significantly enhanced melt strength and strain‐hardening behaviors. The LCB polyolefins also have higher tensile strength, tensile modulus, impact strength and lower elongation at break than their blends. Furthermore, supercritical carbon dioxide (scCO₂) is constructively introduced in the reactive extrusion process. In the presence of scCO₂, the motor current of the twin extruder is decreased and LCB polyolefins with lower melt flow rate (MFR), higher complex viscosity and increased tensile strength and modulus can be obtained. This indicates that the application of scCO₂ can reduce the viscosity of melt in extruder, enhance the diffusion of reactive species, and then facilitate the long chain branching reaction between anhydride group and primary amine group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of use of coupling agents on the properties of microfibrillar composite based on high-density polyethylene and polyamide-6

Microfibrillar composites from high-density polyethylene (HDPE-75 wt%) and polyamide-6 (PA6-25 wt%) were made through a reactive extrusion at the processing temperature of PA6 in combination with hot stretching to form microfibrillar composites, and injection molding at the melt temperature of HDPE to form final composites. The scanning electron microscope observations demonstrated the formation of the PA6 microfibers during extrusion. Incorporation of PA6 microfibers led to an improvement in both flexural and tensile properties as compared to the neat HDPE. Use of ethylene–glycidyl methacrylate copolymers (E-GMA) in the composites gave the highest tensile modulus, while ethylene, butyl acrylate and maleic anhydride terpolymer (E-BA-MA) led to the highest tensile strength and elongation. The maleic anhydride grafted polyethylene (MAPE) was the most efficient among three coupling agents in improving impact strength. With the addition of 5 wt% E-GMA, E-BA-MA and MAPE, the HDPE/PA6 composites exhibited an improvement of 87, 116, and 387 %, respectively, compared to the uncoupled controls. The PA6 microfibers exhibited a regular orientation along the stretching direction in the presence of 2.5 wt% coupling agents; increasing the loading level of coupling agents caused a reduction in the diameter of PA6 microfibers. FT-IR analyses showed the reactions between PA6 and the coupling agents used.     

聚酰胺树脂扩链剂及扩链研究

合成２种聚酰胺６的扩链剂,将扩链剂分别用于ＰＡ６的扩链研究,不同的扩链剂适合不同端基的ＰＡ扩链反应。随着扩链剂用量的增加,ＰＡ的特性粘数增加,但扩链剂用量超过一定限度时,扩链效果下降,但ＰＡ６原有的端基量下降。     

Fabrication and Properties of Modified Poly(butylene terephthalate) with Two-Step Chain Extension

High-viscosity, low-crosslinked poly(butylene terephthalate) (PBT) from organic chain extenders and inorganic particles are prepared. PBT modification adopted from multifunctional, commercially available chain extension containing nine epoxy groups (ADR9) occurs in the first-step chain extension; hydroxyl addition modified dioxazoline (BOZ) serves as the second step. Anion stratiform inorganic hydrotalcite (HT) is used to adjust the crystallization behavior and damp-heat aging properties of PBT. The reaction between the chain extender and PBT end-groups such as carboxyl (–COOH) and hydroxyl (–OH) enhances the interfacial bonding between the PBT matrix and dispersed HT phases. With a fraction of chain extenders in the PBT matrix, the chain-extended PBT exhibits higher mechanical properties, intrinsic viscosity, average molecular weight, and melt viscosity than those of unmodified PBT. Damp-heat aging resistance measurements show correlation with initial carboxyl content in the resin. Reducing the concentration of carboxyl end-groups in the resin is shown to increase hydrolytic stability. The modified PBT resin can be used in optical fiber communication cable industry for its high level of damp-heat aging resistance as well as good mechanic properties.     

Improvement of polyamide 1010 with silica nanospheres via in situ melt polycondensation

Polyamide 1010 (PA1010) had been prepared by in situ melt polycondensation in presence of silica nanospheres with amine groups on the surfaces (SiO₂ NH₂). Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) measurements demonstrated that the nanosphere surface was grafted with PA1010 chains. Wide angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) measurements showed that the PA1010/SiO₂ NH₂ nanocomposites had a lower degree of crystallinity (χ_c) in comparison with PA1010 and PA1010/SiO₂ nanocomposites. Dynamic mechanical analysis (DMA) indicated that SiO₂ NH₂ nanospheres improved glass transition temperature (T_g), tensile strength and storage modulus of PA1010 since SiO₂–NH₂ nanospheres limited the mobility of PA1010 chains. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Influence of carbon nanotubes with different functional groups on the morphology and properties of PPO/PA6 blends

Carbon nanotubes with different functional groups were prepared and then incorporated into the poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polyamide 6 (PPO/PA6) blend via melt blending. The influence of different carbon nanotubes on the morphology and properties of the blend was studied. The results show that addition of pristine CNTs, CNTs‐OH, CNTs‐NH₂ leads to the evolution of the phase structure of PPO/PA6 (mass ratio: 60/40) blend from sea‐island to cocontinuous, whereas incorporation of CNTs‐COOH does not change the blend morphology due to serious aggregation of the carbon nanotubes. Incorporating different CNTs into PPO/PA6 blend increases the tensile modulus and storage modulus of the blends, whereas decreases slightly the tensile strength. At the same time, the glass transition temperatures (T_g) of PA6 and PPO are enhanced. ΔT_g, the gap between the T_g of PA6 and PPO, decreases with the addition of carbon nanotubes due to the stronger interaction of carbon nanotubes with PA6 than PPO. A similar tendency was found in the storage modulus (G′) and complex viscosity (η*) of the composites. The dispersion state of different carbon nanotubes and their interaction with polymer components are different, which causes the different confinement effect to the macromolecular chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010