Influence of annealing treatment on the heat distortion temperature of nylon‐6/montmorillonite nanocomposites

It has been recognized that the incorporation of nanoscale montmorillonite (MMT) layers into polymer matrix enhances significantly the heat resistance of the resultant nanocomposites, especially for nylon‐6 (N6)/clay nanocomposites (NCNs). In the present work, the heat distortion temperature (HDT) of NCNs, including the intercalated N6/Na‐montmorillonite (Na‐MMT) and the exfoliated N6/organo‐montmorillonite (OMMT) ones, have been investigated for both non‐annealed and annealed testing specimens in comparison with the neat N6. As expected, the incorporation of MMT obviously improved HDT of NCNs, with the highest HDT value obtained in the N6/OMMT system due to its exfoliated nano‐structure. After an annealing treatment at 80°C for 6 hr, the HDT revealed noticeable increase for all the samples, particularly for the intercalated N6/Na‐MMT nanocomposite that showed the highest increment of 34°C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR) techniques were employed to clarify the origin of the variation in HDT after annealing, and the results suggest that the increases in the crystallinity, the glass transition temperature, and the order degree of hydrogen bonding may account for the noticeable increases in the HDT of the nanocomposites after annealing. POLYM. ENG. SCI., 45:1247–1253, 2005. © 2005 Society of Plastics Engineers     

Flame retardant nanocomposites of polyamide 6/clay/silicone rubber with high toughness and good flowability

A novel flame retardant, silicone elastomeric nanoparticle (S-ENP) with T_g of −120 °C and particle size of ∼100 nm has been developed and used as a modifier for polyamide 6 (nylon-6). It has been found that S-ENP can not only increase the toughness and improve the flame retardancy of nylon-6 but also helps unmodified clay exfoliate in nylon-6 matrix. It has been also found that the S-ENP and exfoliated clay platelet in nylon-6 have a synergistic flame retardant effect on nylon-6. A novel flame retardant nanocomposite of nylon-6/unmodified clay/S-ENP with high toughness, high heat resistance, high stiffness and good flowability has been prepared and a mechanism of synergistic flame retardancy has also been proposed.     

Compared structure and morphology of nylon-12 and 10-polyurethane lamellar crystals

A comparative study of the structure and morphology of nylon-12 and 10-polyurethane (10-PUR) lamellar crystals, was carried out. Lamellar crystals were obtained by isothermal crystallization from diluted solution. Electron diffraction of lamellae combined with WAXS data recorded from crystal sediments indicated that nylon-12 crystallized in either α-form or γ-form according to the solvent chosen for crystallization. The α-form was the crystal modification predominant in doubly oriented films of nylon-12 prepared by epitaxial crystallization. On the contrary, 10-PUR invariably crystallized in α-form regardless crystallization conditions. The α-form of nylon-12 and 10-PUR shared the same crystal structure with hydrogen-bonded sheets made of antiparallel chains and stacked with progressive shifting along both b and c directions. Lamellar crystals of nylon-12 in γ-form and 10-PUR in α-form displayed similar morphological features but only the former appeared to be sensitive to temperature. Upon heating the nylon-12 crystals near to melting, the real-time WAXS analysis evidenced the occurrence of a partial γ-to-α crystal transition, and in situ AFM observations revealed the appearing of more or less regular ridges on the crystal surface. None of these changes were observed in 10-PUR crystals when subjected to similar treatment.     

Composites of polyamide 6 and silicate nanotubes of the mineral halloysite: Influence of molecular weight on thermal, mechanical and rheological properties

In this work, the potential of silicate nanotubes of the naturally occurring mineral halloysite as filler for polyamide 6 (PA 6) nanocomposites is evaluated. Several PA 6/halloysite composites with 0 wt% to 30 wt% filler loading using two different grades of PA 6 were prepared. In order to elucidate the influence of molecular weight on the properties of the nanocomposites, mechanical resp. rheological experiments (i) below the glass transition temperature T_g of PA 6, (ii) between T_g and the melting temperature T_m of PA 6 and (iii) above T_m were performed. Our investigations reveal that the addition of halloysite nanotubes favours the formation of the γ-modification for the low molar mass PA 6. Furthermore, the storage modulus, the tensile modulus and the yield stress of the composites increase with concentration of halloysite, an effect which is strongly pronounced at very low filler fractions for the low molar mass PA 6 composites. The increase of the storage modulus which was measured in dynamic-mechanical experiments is mostly dominant in the temperature interval from 55 °C to 100 °C, i.e. above the glass transition temperature of PA 6. Rheological investigations showed that the shear viscosity is only moderately increased by the addition of a low fraction of halloysite to PA 6, and nanocomposites with 30 wt% halloysite can be still processed. In summary, halloysite nanotubes are promising and inexpensive candidates for increasing the stiffness of PA 6 while maintaining very good flow properties.     

Preparation,structure and properties of comb-branched waterborne polyurethane/OMMT nanocomposites

Comb-branched waterborne polyurethane/organo-montmorillonite (CWPU/OMMT) nanocomposites were prepared by in situ intercalating polymerization process based on the main materials including IPDI, DMPA, polycaprolactone diols, comb-branched polymeric diols and OMMT. The average particle size of emulsion increases and the particle size distribution of emulsion becomes broader with the increase of OMMT content. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) show that OMMT is homogeneously dispersed into the CWPU matrix with intercalated or exfoliated structure. The properties of CWPU/OMMT nanocomposites are dependent on OMMT content. When the OMMT content is 3 wt%, CWPU/OMMT nanocomposite exhibits excellent overall properties: the particle size of emulsion 63.6 nm, tensile strength 42.0 MPa, E′ 20.3 MPa at 80 °C, water absorption 13% at 24 h and surface contact angle for water over 100°.     

Synthesis and characterization of polyester-based nanocomposites coatings for automotive pre-coated metal

Polyester-based nanocomposites coatings were synthesized by the in situ polymerization with high speed homogenizer process at the various contents of organic modified montmorillonite (OMMT) to disperse into the polyester matrix. The dispersion state of organoclay was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absence of reflection pattern of organoclay and TEM study revealed that organoclay was partially intercalated and exfoliated into the polymer matrix. Mechanical property of polyester-based nanocomposites coatings (PE/OMMT) improved the tensile strength and good formability at the deep drawing test. The viscoelastic behavior of PE/OMMT nanocomposites coatings was observed by dynamic mechanical analysis (DMA). When the content of organoclay was increased, the stiffness of the PE/OMMT nanocomposites coatings increased considerably and T_g of each cured coatings shifted to a lower temperature. Anti-corrosion property was examined by the salt spray test. CNC-3 had little rust after 600 h and it implies that nano-sized layered silicate of organoclay effectively increases the length of the diffusion pathways water molecules. And nano-sized layered silicate of organoclay might be decreased the permeability and could make higher corrosion resistance of PE/OMMT nanocomposites coatings. From those results, CNC-3 had good formability in the deep drawing and also had good anti-corrosion property. So, CNC-3 would be an appropriate coating for automotive pre-coated metal.     

Segmented copolymers of uniform tetra-amide units and poly(phenylene oxide): 1. Synthesis and thermal-mechanical properties

Copolymers of telechelic poly(2,6-dimethyl-1,4-phenylene ether) segments with terephthalic methyl ester endgroups (PPE-2T), 13 wt% crystallisable tetra-amide segments of uniform length (two-and-a-half repeating unit of nylon-6,T) and dodecanediol (C12) as an extender were made via a polycondensation reaction in the melt. The maximum reaction temperature was 280 °C. The PPE-2T/C12/T6T6T copolymers are semi-crystalline materials with a T_g around 170 °C, a melting temperature of 264-270 °C and a T_g/T_m ratio of above 0.8. The modulus is high up to the T_g, which is not achievable in a blend of PPE and polyamide. The most probable morphology is that of long crystalline nano-ribbons in the amorphous matrix. The materials are slightly transparent and have good solvent resistance, low water absorption and good processability.     

Melting behavior of poly(l-lactic acid): X-ray and DSC analyses of the melting process

To clarify the melting behavior of poly(l-lactic acid) (PLLA), the wide-angle X-ray diffraction patterns of the isothermally crystallized PLLA samples (ICSs) were successively obtained during heating. We have already suggested the discrete change in the crystallization behavior of PLLA at a crystallization temperature (T_c) of 113 °C (= T_b) and formation of two crystal modifications for the ICSs obtained in the temperature range T_c ≤ T_b and T_c ≥ T_b. It was elucidated from the change in the X-ray diffraction pattern that the phase transition from the low-temperature crystal modification (α′-form) to the high-temperature one (α-form) occurred in a range 155-165 °C for the ICSs(T_c ≤ T_b), and that the crystal structure for the ICSs(T_c ≥ T_b) did not change. Recrystallization during heating, which is the origin of the multiple melting behavior, was proved by the increase in the diffraction intensity before steep decrease due to the final melting. A temperature derivative curve of the X-ray diffraction intensity almost coincided with the DSC melting curve.     

Free volume sizes in intercalated polyamide 6/clay nanocomposites

The effect of incorporating modified clay into a polyamide 6 (PA6) matrix, on the free volume cavity sizes and the thermal and viscoelastic properties of the resulting nanocomposite, was studied with positron annihilation lifetime spectroscopy, differential scanning calorimetry and dynamic mechanical analysis. At low concentrations of clay the fraction of PA6 crystals melting close to 212 °C was increased, while the fraction of the α-form PA6 crystals, melting close to 222 °C, was reduced. At higher concentrations of clay, a crystal phase with increased thermal stability emerged. Addition of more than 19 wt% clay caused a reduction of the heat of fusion of PA6. An unexpected reduction of the ΔC_p at the glass transition, contradicting the measured reduction of the heat of fusion, was detected, indicating an altered mobility in the non-crystalline regions. The viscoelastic response of PA6/clay nanocomposites, as compared to unfilled PA6, pointed towards a changed mobility in the non-crystalline regions. At high concentrations of clay (>19 wt%) an increase of the free volume cavity diameter was observed, indicating a lower chain packing efficiency in the PA6/clay nanocomposites. The increased free volume sizes were present both above and below the glass transition temperature of PA6.     

Real-time investigation of crystallization in nylon 6-clay nano-composite probed by infrared spectroscopy

Via time-resolved FTIR, we examined the real-time investigation of the structural change in molecular chain of nylon 6 during crystallization of neat nylon 6 and the corresponding nano-composite (N6C3.7) having fully exfoliated structure. The neat nylon 6 predominantly formed α-phase in the crystallization temperature (T_c) range of 155-195 °C. For N6C3.7 crystallization at low T_c range of 150-168 °C, where the network structure formed by the dispersed clay particles still affected chain folding of nylon 6, the formation of the γ-phase was dominant. The crystallization took place so rapidly (less than 1 s) without induction time of crystallization. At high T_c range (=177-191 °C), the stable growth of the α-phase crystal coexisting with γ-phase occurred in N6C3.7 crystallization. The growth mechanism in the subsequent crystallization processes (amides IIIα and IIIγ) was virtually the same in both N6C3.7 and neat nylon 6.     

Microfibrillar composites based on polyamide/polyethylene blends. 1. Structure investigations in oriented and isotropic polyamide 6

The present paper discloses the structural changes caused by heating of polyamide 6 (PA6) samples with different thermal and mechanical histories in the 30-240 °C range. Wide and small-angle X-ray scattering (WAXS and SAXS) of synchrotron radiation, as well as solid-state nuclear magnetic resonance spectroscopy (NMR) measurements are performed. The NMR spectra show that in both isotropic and oriented samples there is a co-existence of α and γ-PA6 crystalline forms. Deconvolution of the WAXS patterns is performed to follow the temperature dependence of the unit cell parameters of the α and γ-forms and also of the equatorial (ECI) and total crystallinity indexes (CI), evaluating the contributions of the two crystalline phases. Estimates for the long spacing and for the average thicknesses of the crystalline (l_c) and amorphous (l_a) phases within the lamellae are calculated as a function of the heat treatment employing analysis of the linear correlation function calculated from the SAXS patterns. The X-ray results allowed the conclusion that upon heat treatment up to 160-200 °C, intensive transitions between the PA6 crystalline forms take place, whereby the content of the initial major crystalline phase decreases and that of the initial minor one increases reaching almost 1:1. Close to 200 °C a general trend toward increasing the content of the α-form is registered. The influence of annealing and quenching after melting on the PA6 crystalline structure is also studied.     

The thermal conductivity of Nylon 6/clay nanocomposites

Nylon 6/clay nanocomposites (NCNs) of different clay loadings are prepared by melt compounding. The effects of clay loading and dispersion on the thermal conductivity of NCNs are investigated using XRD, TEM, DSC, and POM. The results show that the thermal conductivity of the exfoliated NCNs decreases with an increase of clay content; but the thermal conductivity of the intercalated NCNs does not decrease, indeed, it increase markedly at high clay content. Such results observed in the exfoliated NCNs are opposite to the expectation of the classic Maxwell thermal conduction model. The further investigations indicate that such decrease observed in the exfoliated NCNs is due mainly to the exfoliation of clay layers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High improvement in the properties of exfoliated PU/clay nanocomposites by the alternative swelling process

In this work, a stable de-aggregated solvent-swollen organic modified clay, ALA-MMT, suspension is prepared by an efficient solvent swelling process using a home-made shaking mixer. It is found that the estimated average size of the as-prepared organoclay particles in the suspension is reduced to about 155 nm, which has not been reported before. The X-ray diffraction (XRD) patterns confirm that the d-spacing of the silicate layers of the solvent-swollen ALA-MMT expands from 1.4 nm to about 2.1 nm. The de-aggregated solvent-swollen ALA-MMT suspension is then used with polyurethane (PU) to prepare a series of highly exfoliated and high-organoclay-loading nanocomposites, PU/ALA-MMT. Both the XRD patterns and the TEM photographs of the as-prepared PU/ALA-MMT nanocomposites indicate that the organoclay is uniformly dispersed in the PU matrix with a highly exfoliated morphology structure of up to 7 wt% loading. Meanwhile, the TEM photographs give the first report for PU/clay nanocomposites which are almost completely exfoliated, and ∼1-nm thin silicate nanolayers are homogeneously dispersed in the polymer matrix with a high aspect ratio of 30-100. The thermal, mechanical, and anti-corrosion properties are all tremendously enhanced for the as-prepared nanocomposites. The results obtained for the PU nanocomposite with 7 wt% ALA-MMT loading (PUC7) reveal a 19 °C increment in T_g, a 48 °C increment in T_5%, a 248% increase in the tensile strength, and a 123% increase in the elongation. The stainless steel disk (SSD) coated with PUC7 shows the lowest corrosion rate of 2.01 × 10⁻⁶ mm/year, which is 469% lower than that of the SSD coated with pure PU. The reinforcements are much greater than the previously reported PU/clay nanocomposites with comparable clay loadings ascribed to the exceptional homogeneity of as-prepared nanocomposites, which are accredited largely to the stable de-aggregated solvent-swollen organoclay suspension generated by the efficient solvent swelling process.     

Segmented copolymers of uniform tetra-amide units and poly(phenylene oxide): 2. Crystallisation behaviour

The crystallisation behaviour of copolymers of telechelic poly(2,6-dimethyl-1,4-phenylene ether) segments with terephthalic methyl ester endgroups (PPE-2T), 13 wt% crystallisable tetra-amide segments of uniform length units (two-and-a-half repeating unit of nylon-6,T) and dodecanediol (C12) was studied. The crystallisation rate of the T6T6T units was found to be very high despite the high T_g/T_m ratio. The supercooling (T_m−T_c) as measured by DSC is 18 °C at a cooling rate of 20 °C/min. WAXD has elucidated that the tetra-amide units remain organised in the melt.     

Polybenzoxazine/clay hybrid nanocomposites: influence of preparation method on the curing behavior and properties of polybenzoxazines

Several types of polybenzoxazine/clay hybrid nanocomposites have been prepared from organically modified montmorillonite (OMMT) and mono- or bifunctional benzoxazine, 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine (Pa) or bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) isopropane (Ba), respectively. OMMT was prepared by a cation exchange of montmorillonite (MMT) with ammonium salts of amines such as tyramine, phenylethylamine, aminolauric acid, and dodecyl amine. Polybenzoxazine/clay nanocomposites were prepared by two different methods, namely melt method and solvent method. Melt method employs the blending of benzoxazine and OMMT above the melting point of benzoxazine without solvent. In the solvent method, OMMT was dispersed in an organic solvent and then blended with benzoxazine. XRD measurements of the polybenzoxazine/clay hybrid nanocomposites showed that the blending method and the kind of solvent play crucial roles in the dispersion of OMMT in the polybenzoxazine matrix. DSC showed that the inclusion of any type of OMMT significantly lowered the curing exotherm of benzoxazines. The hybrid nanocomposites exhibited higher T_g values than the pristine resins. Dynamic and isothermal TGA clearly showed that the thermal stability was improved by the inclusion of clay.     

Binary and ternary nanocomposites based on PVDF,PMMA, and PVDF/PMMA blends: polymorphism,thermal, and rheological properties

Binary and ternary nanocomposites based on poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA), and PVDF/PMMA blends were successfully prepared through a melt-mixing process, using a commercial organoclay (15A) as the nanofiller. The 15A was more finely dispersed (intercalated/partially exfoliated) within the PVDF matrix compared with the PMMA matrix. A higher PVDF content in the ternary composite essentially led to a superior degree of 15A dispersion. The 15A addition induced the polar β-form PVDF crystals, whereas the presence of PMMA in ternary composites reduced the efficiency in promoting β-form formation by 15A. Adding 15A also enhanced the nucleation of PVDF, but the enhancement was inferior while PMMA was present. Conversely, the crystal growth of PVDF was retarded with the existence of 15A, and the PVDF/15A binary composite exhibited the greatest retardation. The equilibrium melting temperature (T_m°) of PVDF in the neat state and in the blends increased after 15A addition. The PVDF/15A binary composite possessed an evidently higher β-form T_m° than the α-form T_m° of neat PVDF (~20.1 °C rise). Similar effects on the individual components, 15A declined the thermal stability of PVDF but increased that of PMMA in the ternary composites. Rheological property measurements revealed that the ternary composites performed in-between that of individual PVDF/15A and PMMA/15A binary composites. A percolation of 15A (pseudo)network structure was developed in the composites, and a more elastic behavior was observed with increasing PVDF content in the composites.     

Exfoliation of organoclay nanocomposites based on polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) copolymer: Solution blending versus melt blending

Exfoliated nanocomposites based on polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) (SI2VP triblock) copolymer were prepared by solution blending and melt blending. Their dispersion characteristics were investigated using transmission electron microscopy, X-ray diffraction, and small-angle X-ray scattering (SAXS). For the study, SI2VP triblock copolymers with varying amounts of poly(2-vinylpyridine) (P2VP) block (3, 5, and 13 wt%) and different molecular weights were synthesized by sequential anionic polymerization. In the preparation of nanocomposites, four different commercial organoclays, treated with a surfactant having quaternary ammonium salt, were employed. It was found from SAXS that the microdomain structure of an SI2VP triblock copolymer having 13 wt% P2VP block (SI2VP-13) transformed from core-shell cylinders into lamellae when it was mixed with an organoclay. It was found further that the solution-blended nanocomposites based on a homogeneous SI2VP triblock copolymer having 5 wt% P2VP block (SI2VP-5) gave rise to an exfoliated morphology, irrespective of the differences in chemical structure of the surfactant residing at the surface of the organoclays, which is attributable to the presence of ion-dipole interactions between the positively charged N⁺ ion in the surfactant residing at the surface of the organoclay and the pyridine rings in the P2VP block of SI2VP-5 and SI2VP-13, respectively. Both solution- and melt-blended nanocomposites based on microphase-separated SI2VP-13 having an order-disorder transition temperature (T_ODT) of approximately 210 °C also gave rise to exfoliated morphology. However, melt-blended nanocomposite based on a high-molecular-weight SI2VP triblock copolymer having a very high T_ODT (estimated to be about 360 °C), which was much higher than the melt blending temperature employed (200 °C), gave rise to very poor dispersion of the aggregates of organoclay. It is concluded that the T_ODT of a block copolymer plays a significant role in determining the dispersion characteristics of organoclay nanocomposites prepared by melt blending.     

Self‐nucleation behaviors of olefinic blocky copolymer/montmorillonite nanocomposites with collapsed and intercalated clay layers

The self‐nucleation behavior of olefinic blocky copolymer (OBC) / organically modified montmorillonite (OMMT) nanocomposites with a novel collapsed clay structure (c‐OMMT) was studied and compared with that of the nanocomposites with an intercalated clay structure (OBC/i‐OMMT). Their behaviors appear different in three temperature domains, Domain I (D_I) in which the polymer is completely melted and only the heterogeneous nuclei are present, Domain II (D_II) in which only self‐nucleation occurs and Domain III (D_III) where both self‐nucleation and annealing take place. As the OMMT loading increases, the boundary temperature of D_I and D_II (T_I→II) shifts to lower temperature and D_II becomes narrower. For the OBC/c‐OMMT nanocomposites, the T_I→II or T_I→III (the boundary temperature of D_I and D_III) can be lower than the end melting temperature ( ) and leads to appearance of a subdomain of D_I, D_I′, in which the self‐nuclei of un‐melted fragmental crystals exist but the following crystallization is still initiated by c‐OMMT. D_II may even disappear at high c‐OMMT loadings. By contrast, the T_I→II of the OBC/i‐OMMT nanocomposites is always approximate to or higher than the . D_II does not disappear and no D_I′ is observed for the OBC/i‐OMMT nanocomposites. The nucleation efficiency of c‐OMMT is also evidently higher than that of i‐OMMT. These results verify that the c‐OMMT has stronger nucleation ability than i‐OMMT at the same OMMT loading. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41771.     

Effects of annealing (solid and melt) on the time evolution of polymorphic structure of PA6/silicate nanocomposites

The effects of annealing including solid-state annealing (190 °C) and melt-state annealing (230 and 250 °C) on the polymorphic behavior and thermal property of polyamide 6 (PA6)/layered-silicate nanocomposites (PA6LSN) have been investigated as a function of annealing time using Modulated Differential Scanning Calorimetry (MDSC) and wide angle X-ray diffraction. For comparison, thermal behavior and polymorphism of pure PA6 were also studied. It was demonstrated that PA6LSN and PA6 exhibited a similar polymorphic behavior when they were annealed in the solid state for different time duration. As the annealing temperature was elevated to 230 and 250 °C, significant differences in thermal behavior and polymorphism between PA6LSN and PA6 could be found. For example, the γ phase became the absolutely dominating for PA6LSN, while the α crystal was the most predominant phase in neat PA6. Moreover, a new endothermic peak is observed around 235 °C in all PA6LSN MDSC scans, which might be related to the melting of PA6 lamellae formed in the confined environment on the surface of the nano-silicate.     

Exfoliated PA6,6 nanocomposites by modification with PA6

Minor amounts of a fully exfoliated PA6/commercial OMMT nanocomposite were used as a master-batch to produce exfoliated PA6,6 based nanocomposites. The major component PA6,6, which was fully mixed with PA6, did not largely affect the interactions between the OMMT and the surrounding polymer, as the exfoliation level of OMMT increased upon blending with PA6,6. Both the phase behaviour and the mechanical properties of the nanocomposites were compared with those of the PA6,6-rich matrix, to assess the separate effects of the PA6 and the OMMT. The large exfoliation level attained, led to increases in the modulus of elasticity that reached 46% with 5 wt% OMMT, and to the presence of highly ductile materials up to 3 wt% OMMT content.