Combining In‐Situ Organic Modification of Montmorillonite and the Latex Compounding Method to Prepare High‐Performance Rubber‐Montmorillonite Nanocomposites

Summary: To improve the interfacial interaction in MMT‐SBR nanocomposites, one type of UOAC was introduced to in‐situ modified MMT before latex compounding with SBR. The influence of the UOAC/MMT ratio on the structure and properties of MMT/SBR nanocomposites were carefully studied by XRD, TEM, and mechanical testing. It was found that through the in‐situ organic modification, a rubber‐intercalated structure of MMT was obtained in the nanocomposites, and the amount of rubber‐intercalated structure strongly depended on the UOAC/MMT ratio. The tensile strength of MMT‐SBR nanocomposites was enhanced dramatically from 4 to 18 MPa by in‐situ organic modification of MMT.

Stress‐strain diagram of SBR/clay nanocomposites.     

EVA Copolymer Based Nanocomposites

Nanocomposites are a new class of polymer material with an ultrafine phase dispersion of the order of a few nanometers that shows very interesting properties often very different from those of conventional filled polymers. In this work the mechanical and optical properties of Poly[ethylene‐co‐(vinyl acetate)] (EVA copolymer) based nanocomposites have been investigated to evaluate its possible use in several applications. For example, films for covering greenhouses made by EVA copolymer are appealing because of their interesting optical properties and for the so‐called greenhouse effect. Mechanical properties, and the rigidity in particular, are, on the contrary, quite low. Nanocomposites should avoid this shortcoming if optical properties and processability are not unfavorably effected. EVA copolymer based nanocomposites have been prepared by compounding polymer matrix and two different functionalized silicates (0–10 wt.‐%) in molten state. X‐Ray diffractograms show that the in the adopted experimental conditions no exfoliation of the filler is obtained, but an intercalated morphology is observed. Rheological behavior both in shear and in non‐isothermal elongational flow is only slightly influenced by the presence of the filler. As for the mechanical properties, the elastic modulus strongly increases without any worsening of the elongation at break. The permeability in the UV region is not influenced by adding even relatively high contents of the silicates. The improved mechanical and optical properties and the unmodified processability suggest then the use of these new polymeric systems in many applications and in particular as films for covering greenhouses.

UV spectra of the EVA/Nanofil system.     

Evaluation of Coupling Agents in Poly(propylene)/Fly Ash Composites: Effect on Processing and Mechanical Properties

Composites containing 50 wt.‐% fly ash in a PP homopolymer were prepared via batch mixing and compression moulding. The following coupling agents were evaluated: Lubrizol Solplus C800, N,N′‐(1,3‐phenylene)dimaleimide, γ‐methacryloxypropyltrimethoxysilane and maleic‐anhydride‐grafted PP. At the filler level investigated, C800 gave the best balance of composite strength and toughness. In the latter case filler‐matrix adhesion appeared weaker relative to γ‐MPS, BMI and m‐PP, all of which gave excessively strong filler‐matrix adhesion leading to a reduction in composite toughness. The unexpected weakness of the C800/fly ash interaction may be related to removal of surface calcium ions from the fly ash via reaction of a single calcium ion with two C800 molecules.

     

Direct Melt Extrusion Processing of Nylon 6/Clay Nanocomposites Based on Pristine Montmorillonite

Summary: An original direct melt extrusion processing of nylon 6/clay nanocomposites was reported based on pristine (Na⁺‐based) montmorillonite as well as a simple approach using a typical two‐screw extruder. By the application of intercalation agents as the thermodynamic assistants, this method is as an appropriate procedure for industrialized manufacture together with much lowered production cost. Interestingly enough, the synergistic effects of montmorillonite with other inorganic particulates was observed for the first time here.

X‐ray diffraction patterns of pristine MMT and nylon 6/MMT composites with grouped intercalation agents.     

Production of Thermoplastic Starch/MMT‐Sorbitol Nanocomposites by Dual‐Melt Extrusion Processing

A “green” processing method, dual‐melt extrusion, was used to prepare thermoplastic starch/montmorillonite nanocomposites without organic reactions in the solution. XRD demonstrates that sorbitol enlarged the interlayer distance of MMT during the first step. MMT‐sorbitol, formamide and starch were used to obtain TPS/MMT nanocomposites in the second step. XRD and TEM reveal that TPS intercalated the layers of MMT. With increasing MMT content, improvements in thermal stability, tensile strength, Young's modulus and energy break, and a slight decrease of elongation at break, appeared. The effect of water content on the tensile strength and elongation at break was also studied.

     

Segmented Block Copolymers with Monodisperse Hard Segments: The Influence of H‐Bonding on Various Properties

The properties of segmented‐copolymer‐based H‐bonding and non‐H‐bonding crystallisable segments and poly(tetramethylene oxide) segments were studied. The crystallisable segments were monodisperse in length and the non‐hydrogen‐bonding segments were made of tetraamidepiperazineterephthalamide (TPTPT). The polymers were characterised by DSC, FT‐IR, SAXS and DMTA. The mechanical properties were studied by tensile, compression set and tensile set measurements. The TPTPT segmented copolymers displayed low glass transition temperatures (T_g, ?70 °C), good low‐temperature properties, moderate moduli (G′ ≈ 10–33 MPa) and high melting temperatures (185–220 °C). However, as compared to H‐bonded segments, both the modulus and the yield stress were relatively low.

     

The Anisotropy of Fibrillar Silicate/Rubber Nanocomposites

Summary: Fibrillar silicate (FS)/rubber nanocomposites were successfully prepared by directly mixing modified FS with rubber matrix. It is found that FS could be separated into nano‐fibrils with diameters less than 100 nm by the shear forces during mixing. The stress‐strain characteristics of these composites are similar to those for short micro‐fiber/rubber composites (SFRC). Nevertheless, these FS/rubber composites have some outstanding advantages over the conventional SFRC, even though the reinforcing effect of FS is restricted due to its small shape aspect ratio. More importantly, the differences in mechanical properties of the composites in the two different directions show that SBR/FS and NBR/FS composites both exhibit obvious anisotropy, which strongly depends on the preparation process, FS concentration, and rubber matrix. These factors were thoroughly investigated in this paper, and it can be concluded that the anisotropy of the composites was due to the orientation of nano‐fibrils.

     

Recent Advances for Intumescent Polymers

Summary: This paper reviews recent approaches for making intumescent systems. The mechanisms of action involving intumescence are described and commented on. Synergistic aspects using zeolites and organoclays are also considered and discussed. New strategies are examined on the basis of the mechanism of intumescence. The approach of using char forming polymers as additives (blend technology) is also fully discussed. This consists of substituting classical polyols (char forming agents) with char forming polymers (polyamides and thermoplastic polyurethane). It will be shown that the advantages of this concept are to obtain flame‐retarded (FR) polymer blends with improved mechanical properties in comparison with polymers loaded with classical formulations, and the avoidance of problems due to the water solubility of the polyols and their migration. The “nanocomposite approach” enhances the performance of intumescent systems by using a nanostructured char forming polymer. It will be shown that this combination of intumescence via the blending approach and nanocomposites enhances both flame retardancy and mechanical properties, and allows many specifications to be produced (for example, the design of EVA‐based materials for flame retarded low voltage cables and wire). This appears to be one of the most promising ways for designing new efficient intumescent materials.

Intumescent residue after LOI test of an intumescent poly(propylene).     

Intercalated PS/Na+‐MMT Nanocomposites Prepared by Ultrasonically Initiated In Situ Emulsion Polymerization

Summary: A new technique, ultrasonically initiated in situ emulsion polymerization, was employed to prepare intercalated polystyrene/Na⁺‐MMT nanocomposites. FTIR, XRD, and TEM results confirm that the hydrophobic PS can easily intercalate into the galleries of hydrophilic montmorillonite via ultrasonically initiated in situ emulsion polymerization, taking advantages of the multi‐effects of ultrasonic irradiation, such as dispersion, pulverization, activation, and initiation. Properly reducing SDS concentration is beneficial to widen the d‐spacing between clay layers. However, the Na⁺‐MMT amount has little effect on the d‐spacing of nanocomposites. The glass transition temperature of nanocomposites increased as the percentage of clay increased, although the average molecular weight of PS decreased, and the decomposition temperature of the 1obtained nanocomposites moves to higher temperature.

TEM of PS/Na⁺‐MMT nanocomposite prepared by ultrasonically initiated in situ emulsion polymerization.     

Polysulfone/Clay Nanocomposites by in situ Photoinduced Crosslinking Polymerization

PSU/MMT nanocomposites are prepared by dispersing MMT nanolayers in a PSU matrix via in situ photoinduced crosslinking polymerization. Intercalated methacrylate‐functionalized MMT and polysulfone dimethacrylate macromonomer are synthesized independently by esterification. In situ photoinduced crosslinking of the intercalated monomer and the PSU macromonomer in the silicate layers leads to nanocomposites that are formed by individually dispersing inorganic silica nanolayers in the polymer matrix. The morphology of the nanocomposites is investigated by XRD and TEM, which suggests the random dispersion of silicate layers in the PSU matrix. TGA results confirm that the thermal stability and char yield of PSU/MMT nanocomposites increases with the increase of clay loading.

     

Preparation and Combustion Properties of Flame Retardant Nylon 6/Montmorillonite Nanocomposite

Flame retardant Nylon 6 (PA6)/montmorillonite (MMT) nanocomposites have been prepared using direct melt intercalation technique by blending PA6, organophilic clay and conventional fire retardants, such as the melamine cyanurate (MCA) and the combination of decabromodiphenyl oxide (DB) and antimony oxide (AO). Their morphology and combustion properties are characterized by XRD, transmission electron microscopy (TEM), UL‐94 test and Cone Calorimeter experiments. The flame retardant nanocomposites with MCA or DB and AO show lower heat release rate (HRR) peak compared to that of conventional flame retardant PA6. Meanwhile, the synergetic effect was studied between clay and DB‐AO.

TEM of PA‐n nanocomposite.     

Novel Cationic RAFT‐Mediated Polystyrene/Clay Nanocomposites: Synthesis,Characterization, and Thermal Stability

Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.

     

Heat Induced Structure Modifications in Polymer‐Layered Silicate Nanocomposites

Summary: The success of the use of layered silicates in polymer nanocomposites, to improve physical and chemical properties is strictly related to a deeper knowledge of the mechanistic aspects on which the final features are grounded. This work shows the temperature induced structural rearrangements of nanocomposites based on poly[ethylene‐co‐(vinyl acetate)] (EVA) intercalated‐organomodified clay (at 3–30 wt.‐% silicate addition) which occur in the range between 75 and 350 °C. In situ high temperature X‐ray diffraction (HT‐XRD) studies have been performed under both nitrogen and air to monitor the modifications of the nanocomposite structure at increasing temperatures under inert/oxidative atmosphere. Heating between 75 and 225 °C, under nitrogen or air, causes the layered silicate to migrate towards the nanocomposite surface and to increase its interlayer distance. The degradation of both the clay organomodifier and the VA units of the EVA polymer seems to play a key role in driving the evolution of the silicate phase in the low temperature range. The structural modifications of the nanocomposites in the high temperature range (250–350 °C), depended on the atmosphere, either inert or oxidizing, in which the samples were heated. Heating under nitrogen led to deintercalation and thus a decrease of the silicate interlayer space, whereas exfoliation was the main process under air leading to an increase of the silicate interlayer space.

Heat induced structural modification of EVA‐clay nanocomposite under nitrogen and air.     

Synergism Effect of Montmorillonite and Cellulose Whiskers on the Mechanical and Barrier Properties of Natural Rubber Composites

A series of nanocomposite films based on natural rubber (NR), Na⁺‐montmorillonite (MMT), and cellulose whiskers (W) was prepared, keeping a total filler content equal to 5 wt.‐%. In the binary NR/MMT system, small stacks of intercalated montmorillonites were homogeneously dispersed within the polymer matrix whereas they were clearly lying in the vicinity of cellulose whiskers in the ternary NR/MMT/W blends. The effects of MMT and W on mechanical and gas barrier properties of the nanocomposite films were investigated. A significant increase of the rubbery modulus was obtained upon filler addition. The reinforcing effect was particularly important for the nanocomposite film reinforced with 1 wt.‐% MMT and 4 wt.‐% W. The improvement of the gas barrier properties observed upon filler addition was explained by a tortuosity effect. The calculated tortuosity values indicated that the simultaneous use of MMT and W could greatly slow down the gas diffusion rate in NR. Formation of MMT‐W subassembly should be responsible for this synergism effect.

     

Ternary Gels of a Polymer Blend and a Recycled Oil: Their Use as Bitumen Modifiers

A blend of random ethylene‐vinyl acetate copolymer (EVA) and triblock styrene‐butadiene‐styrene copolymer (SBS) was dissolved in a recycled engine oil to obtain ternary thermoreversible gels. As the temperature was increased, first a network associated with EVA disappeared, and a second one associated with SBS dominated, maintaining the elastic response of the system. The principal advantage of these ternary systems is that their mechanical properties and thermal stability are better than that of binary gels. These gels, made from waste, can be used as bitumen modifiers to obtain binders of improved properties and good stability, which are useful for road surfacing.

Temperature sweeps of elastic modulus performed at a frequency of 1 Hz.     

A Novel Phosphorus‐Containing Poly(ethylene terephthalate) Nanocomposite with Both Flame Retardancy and Anti‐Dripping Effects

Summary: It is a big challenge to improve simultaneously both the flame retardancy and the melt‐dripping resistance of polymeric materials such as PET. In this paper, a novel intumescent flame retardant, DPSPB, was synthesized and blended with copolyester PET‐co‐DDP/O‐MMT nanocomposites, which were synthesized by polycondensation of TPA, EG, DDP, and O‐MMT. The resulting PET‐co‐DDP/O‐MMT/DPSPB nanocomposites exhibit very good flame retardance and dripping resistance, e.g., LOI = 29, UL‐94 V‐0. SEM, XRD, and XPS were used to investigate the relationships between the structures and properties of the composites. It is proved that DPSPB offers excellent protection for the structure of nanocomposites, which is responsible for the good anti‐dripping properties of the nanocomposites.

Residues of copolyesters after combustion: common nanocomposite residue of PDMN (left) and the novel nanocomposite residue of PDMN/DPSPB (right).     

Cover Picture: Macromol. Mater. Eng. 8/2005

Summary: Poly(butylene succinate‐co‐adipate) (PBSA) and organically modified montmorillonite (OMMT) nanocomposites of three different compositions were prepared by melt‐extrusion in a batch mixer. The structure of the nanocomposites was studied using X‐ray diffraction (XRD) and transmission electron microscopy (TEM) that revealed a coexistence of exfoliated and intercalated silicate layers dispersed in the PBSA matrix, regardless of the silicate loading. The degree of crystallinity of PBSA decreases with the addition of OMMT platelets. Dynamic mechanical analysis revealed remarkable increase in flexural storage modulus when compared with that of neat PBSA. Tensile property measurements exhibit substantial increase in stiffness with simultaneous increase in elongation at break of nanocomposites as compared to that of neat PBSA. The effect of clay loading on the melt‐state linear viscoelastic behavior of mixed intercalated/exfoliated nanocomposites was also investigated.

Elongation at break of compression molded annealed samples of neat PBSA and various PBSACNs.     

Preparation of Polystyrene/Clay Nanocomposites by Free‐Radical Polymerization in Dispersion

Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na‐MMT clay was pre‐modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading.

     

Synthesis of Block Copolymers containing Chain‐Controlled Aramid and Fluoroethylene Segments

Summary: Novel block copolymers containing aromatic polyamide (aramid) and fluoroethylene segments were synthesized by a two‐step solution polycondensation. This synthetic method could control the chain‐length of aramid segments and these copolymers could have high structural regularity. The number‐average molecular weight ( ) of one of these polymers is over 2.0 × 10⁴. Incorporating fluoroethylene segments improves the solubility of the resulting polymer compared with conventional aramids.

The synthesis of the fluoroethylene‐aramid block copolymers.     

Ternary Blends to Improve Heat Distortion Temperature and Rheological Properties of PVC

Summary: Binary and ternary blends of PVC mixed with α‐methylstyrene/acrylonitrile‐butadiene‐styrene copolymer (AMS‐ABS) and ethylene/vinyl acetate/carbon monoxide terpolymer (EVA‐CO) are investigated, with the aim to obtain a new PVC based material with an improved heat distortion temperature and good processability. Dynamic Mechanical Thermal Analysis (DMTA) reveals that ternary PVC/AMS‐ABS/EVA‐CO blends exhibit two glass transition temperatures: the lower T_g corresponds to a PVC/EVA‐CO phase and the higher one to a PVC/AMS‐ABS phase. An analysis of PVC respective interactions with AMS‐ABS and EVA‐CO leads to assert that the distribution of PVC in the ternary PVC/AMS‐ABS/EVA‐CO system is basically controlled by the binary immiscible blend composition, taken as Φ AMS‐ABS/Φ EVA‐CO ratio. The inclusion of AMS‐ABS and EVA‐CO to form ternary blends based on PVC, allows to improve heat distortion temperature (owed to the presence of AMS‐ABS), maintaining a low viscosity in the molten state, due to the plasticizing effect of EVA‐CO.

Viscosity function obtained at T = 170 °C from extrusion capillary measurements.