Structure and mechanical properties of poly(l-lactide)/layered silicate nanocomposites

Poly(ε-caprolactone) (PCL) masterbatches with the intercalated and the exfoliated morphology were prepared by ring opening polymerization of ε-caprolactone in the presence of organomodified montmorillonite (MMT) Cloisite 30B. Poly(l-lactide) (PLLA) nanocomposites with Cloisite 30B or PCL masterbatches were prepared by melt blending. The effects of the silicate type, MMT content and the nanocomposite morphology on thermal and mechanical properties of PLLA nanocomposites were examined. The montmorillonite particles in PLLA/Cloisite 30B and PLLA/intercalated masterbatch nanocomposites were intercalated. In contrary to expectations, the exfoliated silicate layers of exfoliated masterbatch were not transferred into the PLLA matrix. Due to a low miscibility of PCL and PLLA, MMT remained in the phase-separated masterbatch domains. The stress-strain characteristics of PLLA nanocomposites, Young modulus E, yield stress σ_y and yield strain ε_y, decreased with increasing MMT concentration, which is associated with the increase in PCL content. The expected stiffening effect of MMT was low due to a low aspect ratio of its particles and was obscured by both plastifying effects of PCL and low PLLA crystallinity. Interestingly, in contrast to the neat PLLA, ductility was enhanced in all PLLA/Cloisite 30B materials and in PLLA/masterbatch nanocomposites with low MMT concentrations.     

Synthesis,structure and mechanical properties of nanocomposites based on exfoliated nano magnesium silicate crystal and poly(acrylamide)

In this study, hydrolyzed polyacrylamide based nanocomposite (HPAM-NC) hydrogels crosslinked by chromium (III) acetate, was synthesized using free radical polymerization. The introduction of magnesium silicate nanocrystals (MSNCs) into the hydrolyzed polyacrylamide (HPAM) network endows the system with enhanced mechanical properties. The successful formation and crystalline behavior of HPAM-NC hydrogels was verified by Fourier Transform Infrared (FTIR) spectroscopy and X-Ray Diffraction (XRD) analyses. Field-Emission Scanning Electron Microscopy (FESEM) and rheology tests showed that the morphology and mechanical properties of HPAM-NC hydrogels were strongly influenced by different content of parameters including concentration of copolymer, nanoparticle and cross-linker. The results showed that this nanocomposite hydrogel is a moldable material so it can expand its application as value-added product.     

Chiral poly(amide-imide)/organoclay nanocomposites derived from pyromellitoyl-bis-l-isoleucine and benzimidazole containing diamine: synthesis, nanostructure, and properties

In this study, a series of polymer–clay nanocomposite materials, consisting of organosoluble poly(amide-imide) (PAI) matrix and dispersed nanolayers of inorganic montmorillonite clay, were successfully prepared by solution dispersion technique. At first, the reactive organoclay was prepared by using protonated l-isoleucine amino acid as a swelling agent for silicate layers of Cloisite Na⁺. Then, organosoluble PAI containing isoleucine amino acid was synthesized through step-growth polymerization reaction of N,N′-(pyromellitoyl)-bis-isoleucine diacid and 2-(3,5-diaminophenyl)-benzimidazole under green condition using molten tetrabutylammonium bromide. This polymer was end-capped with amine end groups near the completion of the reaction to interact chemically with acidic group of organoclay. Finally, PAI/organoclay nanocomposite films containing 2%, 5%, 10%, and 15% of organoclay were prepared via solution intercalation method through blending of organoclay with the PAI solution. Dispersion of the modified clay in the PAI matrix resulted in a nanostructured material containing intercalated polymer between the silicate layers. Structures of exfoliation were confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis data indicated that the addition of organoclay into the PAI matrix increased the thermal decomposition temperatures of the obtained nanocomposites compared to the pure PAI.     

Influence of SEBS-g-MA on morphology, mechanical, and thermal properties of PA6/PP/organoclay nanocomposites

Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organically modified clay (organoclay) toughened with maleated styrene-ethylene-butylene-styrene (SEBS-g-MA) were prepared by melt compounding using co-rotating twin-screw extruder followed by injection molding. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize the structure of the nanocomposites. The mechanical properties of the nanocomposites were determined by tensile, flexural, and notched Izod impact tests. The single edge notch three point bending test was used to evaluate the fracture toughness of SEBS-g-MA toughened PA6/PP nanocomposites. Thermal properties were studied by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). XRD and TEM results indicated the formation of the exfoliated structure for the PA6/PP/organoclay nanocomposites with and without SEBS-g-MA. With the exception of stiffness and strength, the addition of SEBS-g-MA into the PA6/PP/organoclay nanocomposites increased ductility, impact strength and fracture toughness. The elongation at break and fracture toughness of PA6/PP blends and nanocomposites were increased with increasing the testing speed, whereas tensile strength was decreased. The increase in ductility and fracture toughness at high testing speed could be attributed to the thermal blunting mechanism in front of crack tip. DSC results revealed that the presence of SEBS-g-MA had negligible effect on the melting and crystallization behavior of the PA6/PP/organoclay nanocomposites. TGA results showed that the incorporation of SEBS-g-MA increased the thermal stability of the nanocomposite.     

Thermal and mechanical properties of PE/organoclay nanocomposites

Polyethylene/montmorillonite clay nanocomposites were obtained via direct melt intercalation. The clay was organically modified with four different types of quaternary ammonium salts. The objective of this work is to study the use of montmorillonite clay in the production of nanocomposites by means on rheological, mechanical and crystallization properties of nanocomposites and to compare to the properties of the matrix and PE/unmodified clay nanocomposites. In general, the tensile test showed that the yield strength and modulus of the nanocomposites are close to the pure PE. Apparently, the mixture with Dodigen salt seems to be more stable than the pure PE and PE/unmodified clay.     

Polymer-layered silicate nanocomposites based on poly(ε-caprolactone)

Poly(ε-caprolactone) nanocomposites based on montmorillonite modified with hexadecyltrimethylammonium bromide (M-HTAB) were prepared by the in situ polymerization technique. As a result, nano-structured PCL/M-HTAB systems were obtained. It was found that the molecular weight of PCL decreased with an increase in silicate content in the system. Within the investigated range of molecular weight, crystallization behavior of poly(ε-caprolactone) was affected only by the presence of M-HTAB. A silicate loading of higher than 10 wt.% reduced both crystallinity degree and the crystallization rate of PCL. The structure of obtained intercalated nanocomposites depended on the amount of montmorillonite in the systems. The periodicity of clay layers, estimated by X-ray diffraction, was found to be high at increased silicate loading in the nanocomposite. Since PCL and SAN are miscible, an attempt was made to use PCL/M-HTAB systems as a modifier for SAN matrix. Apparently, a quantity as small as 0.66 wt.% of M-HTAB in such blends induced a clear increase in material stiffness. An increase of Young's modulus of more than 40% in comparison to neat SAN was observed at 5.65 wt.% silicate loading.     

Rheological evidence for the microstructure of intercalated polymer/layered silicate nanocomposites

The rheological behavior of intercalated polystyrene/layered silicate nanocomposites was investigated. Both storage and loss moduli increased with silicate loading at all frequencies and showed non‐terminal behavior at low frequencies which is a typical behavior of non‐homogeneous systems with ordered microstructures. The rheological behavior in intercalated polystyrene/layered silicate nanocomposite depends not only on the intercalation of polymers, but also on the alignment of silicate layers. Furthermore, the real time intercalation dynamics of polystyrene into the layered silicate, monitored by rheological measurements, were also consistent with our simple quantitative analysis.     

Investigations on the structural,mechanical, thermal,and electrical properties of Ce-doped TiO2/poly(n-butyl methacrylate) nanocomposites

This study focused on the fabrication of poly(n-butyl methacrylate) (PBMA) nanocomposites with various concentrations of cerium-doped titanium dioxide (Ce–TiO₂) nanoparticles via in situ polymerization technique. The structural characterization and the material properties of all the composites were analyzed by UV–visible, FTIR, XRD, SEM, DSC, TG, and tensile strength measurements. The UV–visible and FTIR studies confirmed the effective inclusion of Ce–TiO₂ nanoparticles into the PBMA matrix. The change in amorphous morphology of PBMA to a crystalline structure was observed from the XRD pattern. The SEM morphology revealed the attachment of nanoparticles in the polymer matrix. The inclusion of Ce–TiO₂ nanoparticles enhanced the glass transition temperature, and thermal stability of the PBMA matrix was revealed from DSC and TG, respectively. The tensile strength of PBMA was greatly enhanced by the addition of Ce–TiO₂ nanoparticles. The AC conductivity, dielectric constant, and dielectric loss studies were also performed in the frequency range 10²–10⁶ Hz, and it was observed that addition of Ce–TiO₂ nanoparticles greatly enhanced the electrical properties of PBMA. The change in dielectric constant with the addition of nanoparticles was correlated with a theoretical modeling study. This work also extended to study the role of Ce–TiO₂ nanoparticles in the reinforcing mechanism of the nanocomposite by comparing the actual tensile strength of the composite with different theoretical modeling. The high dielectric constant and tensile strength of composite are beneficial in designing lightweight and highly efficient nanoelectronic materials based on the family of polybutyl acrylates.

     

Structural characterization and thermal decomposition of layered double hydroxide/poly(p-dioxanone) nanocomposites

Nanocomposites based on layered double hydroxides (LDH) and poly(p-dioxanone) (PPDO) were prepared by melt processing using dodecylbenzene sulfonate (DBS) and 4-hydroxybenzene sulfonate (HBS) as organic modifiers. The incorporation of organic anions in LDH was demonstrated by wide-angle X-ray scattering (WAXS) and Fourier transform infrared (FTIR). The dispersion degree of the organically modified LDHs in the PPDO matrix was analyzed by WAXS, indicating that only the LDH modified with HBS was exfoliated. The effect of the organically modified LDHs on the thermal stability of PPDO was studied using thermogravimetric analysis (TGA). The thermal stability of PPDO matrix was enhanced by the incorporation of the LDH modified with HBS due to the shielding effect of the exfoliated layers. In contrast, the LDH modified with DBS produced a decrease of the thermal stability of PPDO, probably due to hydrolytic decomposition of ester group. The thermogravimetric analysis also showed that the organo-modified LDH did not modify the thermal decomposition mechanism of the polymer, but had an effect on the thermal stability.     

Morphology and thermal properties relationship in poly(p-dioxanone)/layered double hydroxides nanocomposites

Nanocomposites of poly(p-dioxanone) (PPDO) with unmodified and organically modified layered double hydroxide (LDH) have been prepared by melt extrusion method. Dodecyl sulfate was used as organic modifier. The morphology of nanocomposites was analyzed by X-ray diffraction and transmission electron microscopy and their thermal properties by differential scanning calorimetry and thermogravimetric analysis. It has been found that the organic modifier decisively influences the nanocomposite morphology, resulting in a higher level of exfoliation. In addition, the glass transition temperature of nanocomposites was slightly higher than in case of unfilled PPDO. Moreover, the crystallization was delayed by LDH incorporation. The above behavior was ascribed to interactions between carbonyl groups of polymer matrix and hydroxyl groups of LDH, as supported by Fourier transformed infrared analysis. Interestingly, two different crystallization processes have been observed in the nanocomposite of PPDO and organically modified LDH. Unmodified and organo-modified LDH, practically did not alter the final melting point of PPDO. However, the thermal decomposition behavior was clearly influenced by the morphology exhibited by nanocomposites.     

The crystalline and mechanical properties of PLA/layered silicate degradable composites

The poly(lactic acid) (PLA)/montmorillonite (MMT) composites were prepared by melt blending in an internal mixer. The effect of MMT and organically modified MMT (OMMT) addition on crystallization and mechanical preferences has been studied. The DSC results show that the crystallization ability of PLA is improved by MMT or OMMT. The addition of MMT and OMMT increase the crystallinity of PLA from 27.3 to 32.8%, and the cold crystallization temperature (T_CC) of PLA decreases from 93.1 to 88.9°C with the MMT. However, the nucleating effect of MMT is better than that of OMMT due to the velvety surface resulted from the organic modification. The average size of the spherulites in PLA/MMT is smaller than that in PLA/OMMT. The addition of MMT or OMMT increases the tensile strength of PLA from 29.6 to 34.7 MPa and decrease the elongation at break of PLA. The modulus of PLA composites is enhanced rapidly from 338 to 660 MPa by the addition of MMT.     

Estimation of interphase thickness and properties in PP/layered silicate nanocomposites

Nanocomposites were prepared from sodium montmorillonite (NaMMT) and organoclays (OMMT) with different particle sizes as a function of silicate content. Composite structure was characterized by various methods including X-ray diffraction (XRD), scanning electron microscopy (SEM) and rheology. Model calculations were carried out to estimate the thickness and yield stress of the interphase forming in the composites. The results proved the formation of an interphase, but the determination of interphase properties was hampered by several factors. First of all, the particle size of the filler changed quite considerably in PP/OMMT composites in spite of earlier observations and expectations. Particle characteristics changed even further when a relatively small amount (5 vol.%) of functionalized polymer (MAPP) was added to the composite. As a consequence, the estimation of the contact surface between the silicate and the polymer became extremely difficult. In spite of the uncertainties overall values of interphase properties were obtained using the results of all composites prepared. The prediction for the average thickness of the interphase is 0.23 μm and we obtained 51.2 MPa for interphase yield stress, but this estimate neglects the different interactions developing in composites containing the uncoated and the modified silicate, respectively.     

Improve the thermal and mechanical properties of poly(L-lactide) by forming nanocomposites with pristine vermiculite

Poly(L-lactide)(PLLA)/pristine vermiculite nanocomposites were prepared by melt blending in a twin-screw extruder, and the detailed information of vermiculite dispersion state and effect of vermiculite on thermal and mechanical properties were systematically studied. The results show that the dispersion of vermiculite in the matrix is quite well when the loading content does not exceed 3 wt%. Pristine vermiculite can obviously improve the melt-crystallization temperature during the nonisothermal crystallization. Both crystallization time span and spherulitic size of PLLA decrease with the increasing amount of vermiculite under isothermal crystallization condition by enhancing the primary nucleation of PLLA. And the adding vermiculite can also improve the tensile modulus and Izod impact strength of PLLA. The intrinsic mechanism for the nucleating effect of vermiculite on PLLA is proposed to be the epitaxial crystallization and specific interaction between vermiculite and PLLA.     

New poly(amide-imide)s syntheses. VII. Preparation and properties of poly(amide-imide)s derived from 1,5-bis(4-aminophenoxy) naphthalene,trimellitic anhydride,and various aromatic diamines

New bis(phenoxy)naphthalene-containing poly(amide-imide)s having an inherent viscosity in the range of 0.62–1.09 dL/g were prepared by the direct polycondensation of 1,5-bis(4-trimellitimidophenoxy) naphthalene ( I ) and various aromatic diamines using triphenyl phosphite and pyridine as condensing agents in N-methyl-2-pyrrolidone (NMP) in the presence of calcium chloride. The diimide-diacid (I) was prepared by the condensation of 1,5-bis(4-aminophenoxy) naphthalene and trimellitic anhydride. Most of the polymers were soluble in aprotic solvents such as NMP and N,N-dimethylacetamide (DMAc), and afforded transparent, flexible and tough films upon casting from DMAc solutions. Measurements of wide-angle X-ray diffraction revealed that those polymers containing p-phenylene or oxyphenylene groups were characterized as crystalline polymers. Tensile strength and initial moduli of the polymer films ranged from 61–86 MPa and 1.83–2.21 GPa, respectively. Glass transition temperatures of the polymers were in the range of 231–340°C. The melting points of the crystalline polymers ranged from 375–430°C. The 10% weight loss temperatures were above 512°C in nitrogen and 481°C in air. © 1993 John Wiley & Sons, Inc.     

New poly(amide-imide)s syntheses. VIII. Preparation and properties of poly (amide-imide)s derived from 2,3-bis(4-aminophenoxy)naphthalene,trimellitic anhydride,and various aromatic diamines

The new polymer-forming diimide-diacid, 2,3-bis(4-trimellitimidophenoxy) naphthalene (I), was readily obtained by the condensation reaction of 2,3-bis (4-aminophenoxy) naphthalene with trimellitic anhydride. A series of novel aromatic poly (amide-imide)s were prepared by the direct polycondensation of diimide-diacid I with various aromatic diamines using triphenyl phosphite in N-methyl-2-pyrrolidone (NMP)/pyridine solution containing dissolved calcium chloride. The resultant polymers have inherent viscosities in the range of 0.65–1.02 dL/g at 30°C in N, N-dimethylacetamide. These polymers were readily soluble in various organic solvents and could be cast into transparent, tough, and flexible films. Their casting films showed tensile strength at break up to 86 MPa, elongation to break of 5–9%, and initial moduli up to 2.35 GPa. The wide-angle X-ray diffraction revealed that those polymers containing p-phenylene or p-oxyphenylene group are partially crystalline, and the other polymers are evidenced as amorphous patterns. These polymers show a glass transition in the range of 213–290°C in their differential scanning calorimetry (DSC) traces. The thermal stability of the polymers was evaluated by thermogravimetry analysis, which showed the 10% weight-loss temperatures in the range of 508–565°C in nitrogen and 480–529°C in air atmosphere. © 1994 John Wiley & Sons, Inc.     

Enhanced thermal and mechanical properties of poly (vinylidene fluoride) nanocomposites reinforced by liquid-exfoliated graphene

We report the preparation and enhanced thermal and mechanical properties of poly (vinylidine diflouride) (PVDF) nanocomposites reinforced by few-layer graphene flakes which are produced by the direct liquid-phase exfoliation of pristine graphite. Graphene flakes are found to homogeneously disperse in PVDF, reduce the bubble defects and thus the porosity of PVDF, and change PVDF’s crystallinity. Thermogravimetric analysis indicates that graphene can accelerate the fracture of hydrogen bond connecting PVDF and N-Methyl pyrrolidone molecules. 1.5?wt% graphene loading leads to around 20?°C enhancement in the melting temperature of PVDF. The mechanical properties like Young’s modulus (EIT), yield stress (σy), and hardness (H) of the nanocomposites are investigated by nanoindentation technique. A 1.0?wt% loading of graphene is found to increase EIT, σy, and H of PVDF by ～337%, ～102%, and ～228%, respectively.

• Highlights

• Few-layer graphene was produced by liquid-phase exfoliation.

• Graphene were added to PVDF to enhance thermal and mechanical properties of polymer.

• Mechanical properties of PVDF/graphene composite films were investigated by nanoindentation.

     

Organoclay/thermotropic liquid crystalline polymer nanocomposites. III. Effects of fully exfoliated organoclay on morphology,thermal, and rheological properties

A fully exfoliated organoclay in thermotropic liquid crystalline polymer (TLCP) based nanocomposite was prepared by a method combining ultrasonication, centrifugation, solution casting, and heat‐shearing separation. Morphological study showed that the organoclays of 15–25 nm in size dispersed uniformly in TLCP with fully exfoliated structures. The organoclays formed molecular level interactions with TLCP molecules. The interactions did not affect the liquid crystallinity and mesophase structure of TLCP, but they affected the thermal stability and thermal properties of TLCP, increasing the thermal stability and shifting the transition temperatures to the higher ends. Mechanical rheology investigations in the linear viscoelastic region showed that with the exfoliated organoclay in TLCP, more obvious pseudosolidlike behavior appeared in the terminal region. The rigidity of TLCP was enhanced by the presence of the exfoliated organoclay with percolated structures in the TLCP matrix. In steady shear tests, the nanocomposite had the similar shear viscosity and N1 (the first normal stress difference) to those of TLCP in the steady state condition. Percolated structures were easily destroyed by sufficient shear strain and the exfoliated organoclays were oriented along the shear direction, even assisting the neighboring TLCP molecules to align in the flow direction, resulting in a decrease of viscosity and an increase of the N1 slope. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 712–720, 2010     

Synthesis and properties of novel poly(amide-imide)s containing pendent diphenylamino groups

A new dicarboxylic acid, 2,4-bis(N-trimellitoyl)triphenylamine, bearing two preformed imide rings was synthesized from the condensation of 2,4-diaminotriphenylamine and trimellitic anhydride at 1:2 molar ratio. A series of poly(amide-imide)s (PAIs) with inherent viscosities of 0.38-0.66 dl/g were prepared by triphenyl phosphite-activated polycondensation from the diimide-dicarboxylic acid with various aromatic diamines. All the resulting PAIs were readily soluble in a variety of organic solvents and formed strong and tough films via solution casting. These PAIs have useful levels of thermal stability associated with moderately high glass-transition temperatures (259-314 °C) and 10% weight loss temperatures in excess of 530 °C in nitrogen or in air.