Effect of clay exfoliation and organic modification on morphological,dynamic mechanical,and thermal behavior of melt‐compounded polyamide‐6 nanocomposites

Polyamide‐6/clay nanocomposites were prepared employing melt bending or compounding technique followed by injection molding using different organically modified clays. X‐ray diffraction and transmission electron microscopy were used to determine the molecular dispersion of the modified clays within the matrix polymer. Mechanical tests revealed an increase in tensile and flexural properties of the matrix polymer with the increase in clay loading from 0 to 5%. C30B/polyamide‐6 nanocomposites exhibited optimum mechanical performance at 5% clay loading. Storage modulus of polyamide‐6 also increased in the nanocomposites, indicating an increase in the stiffness of the matrix polymer with the addition of nanoclays. Furthermore, water absorption studies confirmed comparatively lesser tendency of water uptake in these nanocomposites. HDT of the virgin matrix increased substantially with the addition of organically modified clays. DSC measurements revealed both γ and α transitions in the matrix polymer as well as in the nanocomposites. The crystallization temperature (T_c) exhibited an increase in case of C30B/polyamide‐6 nanocomposites. Thermal stability of virgin polyamide‐6 and the nanocomposites has been investigated employing thermogravimetric analysis. POLYM. COMPOS., 28:153–162, 2007. © 2007 Society of Plastics Engineers     

Polymer‐Clay Nanocomposites Based on Blends of Polyamide‐6 and Polyethylene

The preparation of polyamide‐6/clay, high‐density polyethylene/clay, and high‐density polyethylene/ polyamide‐6/clay nanocomposites is considered. X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier Transform Infrared (FTIR) measurements show that the clay enhances the crystallization of the γ‐form of polyamide‐6. The clay also acts as a nucleation agent and causes a reduction of spherulitte size. Scanning electron microscopy (SEM) analysis of fracture surfaces shows that the clay reduces the PA‐6 particle size in the HDPE/PA‐6/clay nanocomposites and changes the morphology. Mechanical properties and the effect of maleated polyethylene are also reported.     

Effect of clay addition on the morphology and thermal behavior of polyamide 6

The nanostructure, morphology, and thermal properties of polyamide 6 (PA6)/clay nanocomposites were studied with X‐ray scattering, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The wide‐angle X‐ray diffraction (WAXD) and TEM results indicate that the nanoclay platelets were exfoliated throughout the PA6 matrix. The crystallization behavior of PA6 was significantly influenced by the addition of clay to the polymer matrix. A clay‐induced crystal transformation from the α phase to the γ phase for PA6 was confirmed by WAXD and DSC; that is, the formation of γ‐form crystals was strongly enhanced by the presence of clay. With various clay concentrations, the degree of crystallinity and crystalline morphology (e.g., spherulite size, lamellar thickness, and long period) of PA6 and the nanocomposites changed dramatically, as evidenced by TEM and small‐angle X‐ray scattering results. The thermal behavior of the nanocomposites was investigated with DSC and compared with that of neat PA6. The possible origins of a new clay‐induced endothermic peak at high temperature are discussed, and a model is proposed to explain the complex melting behavior of the PA6/clay nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1191–1199, 2007     

Impact modified polyamide‐6/organoclay nanocomposites: Processing and characterization

The effects of melt state compounding of ethylene‐butyl acrylate‐maleic anhydride (E‐BA‐MAH) terpolymer and/or three types of organoclays (Cloisite® 15A, 25A, and 30B) on thermal and mechanical properties and morphology of polyamide‐6 are investigated. E‐BA‐MAH formed spherical domains in the materials to which it is added, and increased the impact strength, whereas the organoclays decreased the impact strength. In general, the organoclays increased the tensile strength (except for Cloisite 15A), Young's modulus and elongation at break, but the addition of E‐BA‐MAH had the opposite effect. XRD patterns showed that the interlayer spacing for the organoclays Cloisite 25A and Cloisite 30B increased in both polyamide‐6/organoclay binary nanocomposites and in polyamide‐6/organoclay/impact modifier ternary systems. TEM analysis showed that exfoliated‐intercalated nanocomposites were formed. The crystallinities of polyamide‐6/organoclay nanocomposites were in general lower than that of polyamide‐6 (except for Cloisite 15A). In ternary nanocomposites, crystallinities generally were lower than those of polyamide‐6/organoclay nanocomposites. Cloisite 15A containing ternary nanocomposites had higher tensile and impact strengths and Young's modulus than the ternary nanocomposites prepared with Cloisite 25A and Cloisite 30B, owing to its surface hydrophobicity and compatibility with the impact modifier. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

Preparation of thermoplastic elastomer nanocomposites based on polyamide‐6/polyepichlorohydrin‐co‐ethylene oxide

This work is aimed at determining the effect of nanoclay and polyepichlorohydrin‐co‐ethylene oxide (ECO) content on the microstructure and mechanical properties of PA6/ECO thermoplastic elastomers (TPEs). TPE nanocomposites were prepared in a laboratory mixer using polyamide 6 (PA6), ECO, and an organoclay by a two‐step melt mixing process. First, the PA6 was melt blended with Cloisite 30B and then mixed by ECO rubber. X‐ray diffraction results and transmission electron microscopy image showed that the nanoclay platelets were nearly exfoliated in both the phases. The SEM photomicrograph of PA6 with ECO showed that the elastomer particles are dispersed throughout the polyamide matrix and the size of rubber particles is less than 3 μm. Introduction of organoclay in the PA6 matrix increased the size of dispersed rubber particles in comparison with the unfilled but otherwise similar blends. The nanoscale dimension of the dispersed clay results in an improvement of the tensile modulus of the nanocomposites. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Effects of microcompounding process parameters on the properties of ABS/polyamide‐6 blends based nanocomposites

Melt intercalation method was applied to produce acrylonitrile‐butadiene‐styrene/polyamide‐6 (ABS/PA6) blends based organoclay nanocomposites using a conical twin‐screw microcompounder. The blend was compatibilized using a maleated olefinic copolymer. The effects of microcompounding conditions such as screw speed, screw rotation‐mode (co‐ or counter‐), and material parameters such as blend composition and clay loading level on the morphology of the blends, dispersibility of nanoparticles, and mechanical properties were investigated. Furthermore, corotating screws were modified to achieve elongational flow which is efficient for obtaining dispersive mixing. The morphology was examined by SEM analysis after preferential extraction of the minor phase. Subsequently, the SEM micrographs were quantitatively analyzed using image analyzer software. The morphology of the blends indicated that processing with counter‐rotation at a given screw speed yielded coarser morphology than that of processed with corotation. X‐ray diffraction analysis showed that highest level of exfoliation is observed with increasing PA6 content, at 200 rpm of screw speed and in corotation mode. Also, the effects of screw speed, screw rotation mode, and screw modification were discussed in terms of XRD responses of the nanocomposites. The aspect ratio of the clay particles which were measured by performing image analysis on TEM micrographs exhibited a variation with processing conditions and they are in accordance with the modulus of the nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structure,mechanical, and fracture properties of nanoreinforced and HNBR‐toughened polyamide‐6

Hydrogenated nitrile rubber (HNBR) and synthetic nanofillers, viz. water‐swellable sodium fluorohectorite (FH) and water dispersible boehmite alumina (BA), were used to toughen and reinforce polyamide‐6 (PA‐6). FH and BA were introduced in HNBR latex that was dried prior to melt mixing with PA‐6. Binary blend (PA‐6/HNBR) and ternary nanocomposites (PA‐6/HNBR/nanofiller) were produced and their structure–property relationships studied. HNBR was coarsely and microscale dispersed in PA‐6. FH, slightly intercalated, was present in PA‐6 and in the PA‐6/HNBR interphase, whereas BA was mostly located in the HNBR droplets. HNBR improved the ductility of the PA‐6/HNBR blend at cost of stiffness and strength. The fracture toughness and energy, determined on notched Charpy specimens at different temperatures (T = ?30°C, room temperature, and T = 80°C) were improved by blending with HNBR at 9 wt %. Additional incorporation of the nanofillers in 2.5 wt % enhanced the stiffness and strength of the PA‐6/HNBR blend but reduced its ductility. The fracture toughness of the ternary nanocomposites was between those of PA‐6 and PA‐6/HNBR, whereas their fracture energy fairly agreed with that of the parent PA‐6. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effect of clay on the thermal degradation of polyamide 6 in polyamide 6/clay nanocomposites

The degradation pathway of polyamide 6/clay nanocomposites was studied as a function of clay content. Well-dispersed polymer-clay nanocomposites can be easily obtained by simple melt blending between organically-modified clays and polyamide 6. Polyamide 6-clay nanocomposites exhibit a large reduction in the peak heat release rate, 60%, measured by cone calorimetry. There are no significant differences in the evolved products during thermal degradation of polyamide 6 and polyamide 6/clay nanocomposites in terms of composition and functionality. The main degradation pathway of polyamide 6 is aminolysis and/or acidolysis, primarily through an intra-chain reaction, producing ε-carprolactam, which is the monomer of polyamide 6. As the clay loading is increased, the relative quantity of ε-carprolactam in the evolved products decreases and the viscosity of the soluble solid residues increases. It is thought that inter-chain reactions become significant in the presence of clay because the degrading polymer chains are trapped in the gallery space of the clay during thermal degradation.     

Investigation of nanostructure and properties of aromatic–aliphatic polyamide‐based nanocomposites with clay additives

Aromatic–aliphatic polyamide/clay nanocomposites were produced using solution intercalation technique. Surface modification of the clay was performed with ammonium salt of aromatic diamine and the polyamide chains were produced by condensation of 4‐aminophenyl sulfone with sebacoyl chloride (SCC) in dimethyl acetamide. Carbonyl chloride endcapped polymer chains were prepared by adding extra SCC near the end of polymerization reaction. The nanocomposites were investigated for organoclay dispersion, water absorption, mechanical, and thermal properties. Formation of delaminated and intercalated nanostructures was confirmed by X‐ray diffraction and TEM studies. Tensile strength and modulus improved for nanocomposites with optimum organoclay content (8 wt %). Thermal stability and glass transition temperatures of nanocomposites increased relative to pristine polyamide with augmenting organoclay content. The amount of water uptake for these materials decreased as compared with the neat polyamide. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Direct pyrolysis mass spectrometry analyses of polyamide‐6 containing melamine and boron compounds

In this work, the thermal degradation characteristics of polyamide 6 (PA6) containing melamine (Me) and a boron‐containing additive, borophosphate (BPO₄), zinc borate (ZnB) or a boron and silicon‐containing oligomer (BSi) are investigated systematically via direct pyrolysis mass spectrometry. In the presence of boron compounds, not only the release of melamine and its degradation products but also thermal characteristics of PA6 are affected significantly and the interactions between melamine and PA6 are enhanced. For the composite involving BPO₄, sublimation of melamine and degradation of PA6 are slightly shifted to high temperatures. Whereas, for the composites involving ZnB and BSi, sublimation of melamine is depressed due to the glassy surface formed by ZnB and BSi and release of thermal degradation products of PA6 are shifted to lower temperatures noticeably. The glassy surface generated by ZnB allows the release of degradation products of melamine to a certain extent. Conversely, for the composite involving BSi, reduction in the yields of degradation products of melamine is also noted. The trap of degradation products of melamine in the polymer matrix causes significant decrease in the the temperature region where thermal degradation products of PA6 are recorded. POLYM. COMPOS. 34:1389–1395, 2013. © 2013 Society of Plastics Engineers     

Crystallization and thermal behavior of microcellular injection‐molded polyamide‐6 nanocomposites

This article presents the effects of nanoclay and supercritical nitrogen on the crystallization and thermal behavior of microcellular injection‐molded polyamide‐6 (PA6) nanocomposites with 5 and 7.5 wt% nanoclay. Differential scanning calorimetry (DSC), X‐ray diffractometry (XRD), and polarized optical microscopy (POM) were used to characterize the thermal behavior and crystalline structure. The isothermal and nonisothermal crystallization kinetics of neat resin and its corresponding nanocomposite samples were analyzed using the Avrami and Ozawa equations, respectively. The activation energies determined using the Arrhenius equation for isothermal crystallization and the Kissinger equation for nonisothermal crystallization were comparable. The specimen thickness had a significant influence on the nonisothermal crystallization especially at high scanning rates. Nanocomposites with an optimal amount of nanoclay possessed the highest crystallization rate and a higher level of nucleation activity. The nanoclay increased the magnitude of the activation energy but decreased the overall crystallinity. The dissolved SCF did not alter the crystalline structure significantly. In contrast with conventionally injection‐molded solid counterparts, microcellular neat resin parts and microcellular nanocomposite parts were found to have lower crystallinity in the core and higher crystallinity near the skin. POLYM. ENG. SCI., 46:904–918, 2006. © 2006 Society of Plastics Engineers     

Potential in situ preparation of aliphatic polyamide‐based nanocomposites: The organoclay‐polyamide salt interaction

In situ intercalative polycondensation is applied for the preparation of polyamide (PA) n,6–clay nanocomposites, namely poly(ethylene adipamide) (PA 2,6), poly(hexamethylene adipamide) (PA 6,6), and poly(dodecamethylene adipamide) (PA 12,6). For this purpose, two different polymerization routes are considered; a low‐temperature melt polymerization technique and the conventional solution‐melt one. Under the specific experimental conditions, lack of clay exfoliation is detected through XRD measurements, which is proved irreversible even when twin‐screw extrusion is attempted as an additional step. The resulting PA n,6–clay structures are found dependent on the diamine moiety length; more specifically, an intrinsic interaction between the polyamide monomer and the organoclay surfactant is indicated. An ion exchange occurs between the two competitive species, that is, diamine and surfactant cations, leading to flocculated clay structures. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Gasoline permeation behavior and mechanical properties of polyamide 6/nanoclay,polyamide 6/PE‐g‐maleic anhydride blend,and polyamide 6/PE‐g‐maleic anhydride/clay nanocomposite

In this article, polyamide 6 (PA6)/clay nanocomposites, PA6/polyethylene grafted maleic anhydride (PE‐g‐MA) blends, and PA6/PE‐g‐MA/clay nanocomposites were prepared and their gasoline permeation behavior and some mechanical properties were investigated. In PA6/clay nanocomposites, cloisite 30B was used as nanoparticles, with weight percentages of 1, 3, and 5. The blends of PA6/PE‐g‐MA were prepared with PE‐g‐MA weight percents of 10, 20, and 30. All samples were prepared via melt mixing technique using a twin screw extruder. The results showed that the lowest gasoline permeation occurred when using 3 wt % of nanoclay in PA6/clay nanocomposites, and 10 wt % of PE‐g‐MA in PA6/PE‐g‐MA blends. Therefore, a sample of PA6/PE‐g‐MA/clay nanocomposite containing 3 wt % of nanoclay and 10 wt % of PE‐g‐MA was prepared and its gasoline permeation behavior was investigated. The results showed that the permeation amount of PA6/PE‐g‐MA/nanoclay was 0.41 g m^?2 day^?1, while this value was 0.46 g m^?2 day^?1 for both of PA6/3wt % clay nanocomposite and PA6/10 wt % PE‐g‐MA blend. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40150.     

Toughening and brittle‐tough transition in polyamide 12‐organoclay/maleated styrene‐ethylene‐co‐butylene‐styrene nanocomposites

Tough nanocomposites based on polyamide 12 (PA12) can be obtained by the addition of a maleated rubber to a highly dispersed PA12‐clay nanocomposite by melt processing. The nanostructure behavior was evaluated by X‐ray diffraction and transmission electron microscopy. The results showed that the organoclay was highly dispersed and mostly located in the PA12 matrix due to the larger affinity between the polyamide and the clay, but some of the organoclay was also present in the polymer/polymer interface. The presence of organoclay slightly increased the dispersed particle size, indicating decreased compatibilization. This was attributed to a partial shielding of maleic anhydride compatibilizer by surfactant. The addition of the elastomer considerably improved the toughness of the PA12‐based nanocomposites, maintaining its stiffness; i.e., the nanocomposites with 25% rubber content showed an increase of 25‐fold of notched impact strength of the PA12 matrix, meanwhile ductility and stiffness remained constant. This allowed us to obtain toughened PA12 PNs throughout a large range of strain rate and a modulus similar to that of the unmodified PA12. The position of the brittle/tough transition in terms of rubber content, determined by the standard notched Izod test (25% mSEBS) is basically the same as that determined by the essential work of fracture procedure. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Mechanical and electrical properties of polyamide‐6‐based nanocomposites reinforced by fulleroid fillers

The effect of the fulleroid fillers (fullerene C₆₀, mixture of C₆₀/C₇₀ and fulleroids soot) on mechanical, tribological, and electrical properties of the nanocomposites based on polyamide‐6 (PA6) was investigated. The nanocomposites were prepared by in situ polymerization. Both the tensile modulus and tensile strength of polymer composites were improved up to 15% with loading of 0.001–0.1 wt% of fulleroids materials. For nanocomposites with fulleroid fillers, the friction coefficients were practically two times as lower that of neat PA6. Electrical volume resistivity of composites decreases at loading of fulleroid fillers. The minimal electrical volume resistance was about 10⁷ Ω cm at 0.1 wt% loading of fullerene soot. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Glass fiber reinforced polyamide‐6 nanocomposites

Polyamide 6 nanocomposites (PA6/NC) are novel type of composite materials comprising extremely thin, “nanometer scale” dispersions of smectitic silicate platelets. We prepared such PA6/NC materials via a melt compounding technique using suitably organomodified montmorillonite or hectorite type clays. The high surface to volume ratio of such thin silicate dispersions in PA6/NC leads to a high reinforcement efficiency even at 2 to 5 wt% of clay, achieving high specific modulus, strength and heat distortion temperature under load (DTUL). In addition, the platelet orientation and their surface nucleation effects seem to promote a faster crystallization and higher crystallinity in PA‐6/NC (particularly at the surface and in thin‐wall injection moldings), as compared to the standard PA‐6. Such morphological features in PA‐6/NC also result in improved moisture resistance. Recognizing these benefits, we investigated the use of PA‐6/NC as a matrix for making both short and long glass fiber (GF) reinforced composites. Significant improvements in modulus were achievable in both the dry and the moisture conditioned state for PA‐6/NC compared to standard PA‐6, at any given level of glass fiber reinforcement. In general a small amount (3‐4 wt%) of the nanometer scale dispersed clay is capable of replacing up to 40 wt% of a standard mineral filler or 10‐15 wt% of glass fiber in PA‐6 composites to give equivalent stiffness at a lower density or a lower part weight advantage. In addition, improved moisture resistance, permeation barrier and fast crystallization/mold cycle time contribute to the usefulness of such composites.     

Organoclay‐reinforced dynamically vulcanized thermoplastic elastomers of polyamide‐6/polyepichlorohydrin‐co‐ethylene oxide

Dynamically vulcanized thermoplastic elastomers (TPVs) based on polyamide‐6 (PA‐6) and poly(epichlorohydrin‐co‐ethylene oxide) (ECO) and their nanocomposites were prepared via melt‐blending process. The unfilled and organoclay (OC)‐filled TPVs were characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry, thermal gravimetric analysis (TGA), and mechanical tests. XRD and TEM results showed that the OC particles were well exfoliated into the samples with high rubber content while both intercalated and exfoliated structures were found in the samples with low rubber content. The mechanical properties showed that ECO improved the elongation at break and the presence of OC increased the Young's modulus. Also, wide angle XRD analysis showed an increase in α‐crystals of PA‐6 with addition of ECO rubber. Moreover, it was found that by increasing OC content, crystallization temperature increased but the degree of crystallinity decreased. TGA showed that increasing ECO content decreased thermal stability of the samples, while the presence of OC did not have any considerable effect on the thermal stability. POLYM. COMPOS., 38:1948–1956, 2017. © 2015 Society of Plastics Engineers     

Free‐volume hole properties of two kinds thermoplastic nanocomposites based on polymer blends probed by positron annihilation lifetime spectroscopy

Two type of nanocomposites—an immiscible blend, high density polyethylene/polyamide 6 (HDPE/PA‐6) with organomodified clay, and a compatibilized blend, high density polyethylene grafted with acrylic acid/PA‐6 (PEAA/PA‐6) with organomodified clay—were prepared via melt compounding. X‐ray diffraction and transmission electron microscopy results revealed that the clay was intercalated and partially exfoliated. Positron annihilation lifetime spectroscopy has been utilized to investigate the free‐volume hole properties of two type of nanocomposites. The results show a negative deviation of free‐volume size in PEAA/PA‐6 blend, and a positive deviation in HDPE/PA‐6 blend, and I₃ has a greater negative deviation in compatibilized blend than in immiscible blend due to interaction between dissimilar chains. For nanocomposites based on polymer blends, in immiscible HDPE/PA‐6/organomodified clay system, the variation of free‐volume size with clay content is not obvious and the free‐volume concentration and fraction decreased. While in the case of compatibilized PEAA/PA‐6/organomodified clay nanocomposites, complicated variation of free‐volume properties due to interactions between two phases and organomodified clay was observed. And the interaction parameter β shows the interactions between polymers and organomodified clay. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2463–2469, 2006     

Crystal structures and their effects on the properties of polyamide 12/clay and polyamide 6–polyamide 66/clay nanocomposites

Both polyamide 12 (PA 12)/clay and polyamide 6–polyamide 66 copolymer (PA 6/6,6)/clay nanocomposites were prepared by melt intercalation. The incorporation of 4–5 wt % modified clay largely increased the strength, modulus, heat distortion temperature (HDT), and permeation resistance to methanol of the polyamides but decreased the notched impact strength. Incorporation of the clay decreased the melt viscosities of both the PA 12 and PA 6/6,6 nanocomposites. Incorporation of the clay increased the crystallinity of PA 6/6,6 but had little effect on that of PA 12, which explained why the clay obviously increased the glass‐transition temperature of PA 6/6,6 but hardly had any effect on that of PA 12. The dispersion and orientation of both the clay and the polyamide crystals were studied with transmission electron microscopy, scanning electronic microscopy, and X‐ray diffraction. The clay was exfoliated into single layers in the nanocomposites, and the exfoliated clay layers had a preferred orientation parallel to the melt flow direction. Lamellar crystals but not spherulites were initiated on the exfoliated clay surfaces, which were much more compact and orderly than spherulites, and had the same orientation with that of the clay layers. The increase in the mechanical properties, HDT, and permeation resistance was attributed to the orientated exfoliated clay layers and the lamellar crystals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4782–4794, 2006     

Studies on polyamide‐6/polyolefin blend system compatibilized with epoxidized natural rubber

Infrared spectra of polyamide‐6 (PA6) with and without epoxidized natural rubber (ENR) are presented. The influence of ENR used as a compatibilizer on the morphologies, crystallizability, mechanical properties, and thermal behavior of the polyamide‐6/polyolefins (PO) blends are studied. The infrared spectra suggest that under normal processing conditions, the carboxyl end groups of PA6 could chemically react in situ with the epoxy groups of ENR, and ester groups are created. This means that the PA6‐ENR grafting copolymer could be obtained during processing. All the morphological characterizations and thermal analyses show that the compatibility of PA6/PO blends is obviously improved by ENR because the copolymer increases the interaction between PA6 and PO. It is also found that the toughness of PA6/PO blends increase significantly after using ENR, while the tensile strength and the softening temperature of PA6/PO blends have almost no change. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 398–403, 2003