Aramid Chains Research Articles

Fabricating strong and tough aramid fibers by small addition of carbon nanotubes

Synthetic high-performance fibers present excellent mechanical properties and promising applications in the impact protection field. However, fabricating fibers with high strength and high toughness is challenging due to their intrinsic conflicts. Herein, we report a simultaneous improvement in strength, toughness, and modulus of heterocyclic aramid fibers by 26%, 66%, and 13%, respectively, via polymerizing a small amount (0.05 wt%) of short aminated single-walled carbon nanotubes (SWNTs), achieving a tensile strength of 6.44 ± 0.11 GPa, a toughness of 184.0 ± 11.4 MJ m−3, and a Young’s modulus of 141.7 ± 4.0 GPa. Mechanism analyses reveal that short aminated SWNTs improve the crystallinity and orientation degree by affecting the structures of heterocyclic aramid chains around SWNTs, and in situ polymerization increases the interfacial interaction therein to promote stress transfer and suppress strain localization. These two effects account for the simultaneous improvement in strength and toughness.

Preparation and properties of the aramid pulp/nitrile butadiene rubber composites with compatibilization of ionic liquids

AbstractTo improve the uniformity and the mechanical/wear performances of the aramid pulp (AP)/nitrile butadiene rubber (NBR) composites, two types of ionic liquids (ILs), that is, 1‐carboxymethyl‐3‐methylimidazolium chloride ([CmMIM]Cl) and 1‐allyl‐3‐vinylimidazolium chloride ([AVIM]Cl) were applied on the AP surface, respectively. The ILs partially disrupted the hydrogen‐bonds between the aramid chains to mitigate the fiber entanglement, and connected the AP to the rubber matrix by hydrogen‐bond interaction or the crosslinking reaction during the vulcanization. The test results showed that, the IL treatments effectively improved the tensile and tear strengths without obviously affecting the physical characteristics of the composites. The wear properties of the AP/NBR composites also improved due to the enhancements of the tear strength and the connection between the AP and NBR matrix. Compared to the [CmMIM]Cl, the [AVIM]Cl was more efficient to improve the properties attributed to its better compatibilization for the AP/NBR system. For example, the specific wear rate under 20‐N load of the composite with 15‐phr [AVIM]Cl‐AP was 1.1 × 10−7 mm3 N−1 mm−1, which was approximately 25% and 35% lower than that of the composites reinforced with 15‐phr [CmMIM]Cl‐AP and untreated AP, respectively.

In situ Preparation of Aramid-MWCNT Nano-composites: Morphology, Thermal Mechanical and Dielectric Properties

In situ polymerization technique was used to link chemically the amine-terminated high molecular weight aramid chains with acid-functionalized MWCNTs. The The X-ray photoelectron spectroscopy (XPS) was used to study the chemical linkage between aramid chains and MWCNTs and the composite morphology was investigated by scanning electron microscopy. Dynamic mechanical analysis (DMA) showed a higher increase in the storage modulus. The temperature involving α-relaxations on MWCNTs loading was found higher in comparison to the system where pristine MWCNTs were used. Iinterfacial interactions between the matrix and MWCNTs including hydrogen bonding, π–π stacking and chemical bonding are considered the key parameters responsible and the chemical bonding of the MWCNTs with the matrix resulted in better dispersion of CNTs and the higher visco-elastic properties. The maximum glass transition and the thermal decomposition temperature of these composites respectively were observed around 346°C and 533°C. The inclusion of pristine CNTs increased the electric conductivity of the aramid films with a minimum threshold value at the loading of 1.67 vol.%. Such mechanically strong and thermally stable aramid composites are suitable for many applications including high performance materials for electromagnetic shielding and radar absorption.

Effect of functionalized graphene oxide nanosheets on the morphologies and antifouling properties of polyamide composite membranes

The application of carbon‐based nanomaterials in desalination has attracted significant attention. In this study, the modified graphene oxide (GO) is prepared by the reaction of octylamine with the carboxyl groups of GO and is dispersed in (trimesoyl chloride)/n‐hexane solution using the phase inversion method. The polyaramide membrane is prepared via interfacial polymerization using aqueous solution of m‐phenylenediamine and modified GO/(trimesoyl chloride) in n‐hexane. The modified GO is found to be well dispersed in the n‐hexane solvent, which is confirmed by the atomic force microscopy method. The effect of modified GO on the chemical composition and morphology of the aramid membrane surface is studied via Fourier‐transform infrared spectroscopy‐attenuated total reflectance and scanning electron microscopy tests. The results of membrane performance show that the high water flux of the aramid membranes containing the modified GO is attributed to the porosity generation due to nanosheet protrusions and hydrophilic groups on the surface of modified GO. In addition, the increasing the salt rejection parameter can be the result of the interactions between the GO particles and the aramid chains during the interfacial polymerization. The fouling test results show that in the presence of the modified GO in aramid membrane, a hydrated layer of water can be formed on the surface of GO as a result of the presence of hydroxyl and epoxy groups. In high concentrations of modified GO, the presence of octyl hydrophobic agents leads to the ejection of the bovine serum albumin molecules from the membrane surface. J. VINYL ADDIT. TECHNOL., 23:E170–E179, 2017. © 2016 Society of Plastics Engineers

Nanoblends of PMMA/aramid: A study on morphological and physical properties

Motivated by the development of miscible nano-blends with supramolecularly organized structures, relying on intermolecular interactions, novel poly(methyl methacrylate) (PMMA)/aramid nano-blend system was designed. Aramid chains, obtained through the condensation of a mixture of 1,5-diaminonaphthalene and 1,3-phenylenediamine with terephthaloyl chloride, were incorporated in PMMA to form nano-structured blends via physical interlocking. Effect of polymer–polymer interactions on miscibility and macroscopic properties of blends were studied using tensile testing, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Tensile properties well indicated the mechanical compatibility resulting from good component cohesion via hydrogen bonding. DSC results also designated entirely miscible blends even at high aramid content. Morphological observations corroborated these findings as well, however, physical interaction of PMMA with varying aramid content efficiently altered blend morphology. Blends with 10, 20, 60 and 70 wt.% aramid possessed fine patterns owing to nano-level compatibility of two phases. Novel blends holding advanced properties can be potentially exploited to acquire exceptional performance in various technological applications such as nano-templates, nano-structured membranes, nano-devices, etc.

Influence of clay modification on the properties of aramid-layered silicate nanocomposites

Nanocomposites from organoclay and aromatic polyamide were prepared using solution intercalation method. Aramid chains were synthesised by reacting 4-aminophenylsulfone with isophthaloyl chloride in dimethylacetamide. Dodecylamine was used as a modifier to change the hydrophilic nature of montmorillonite into organophilic. Suitable quantities of organoclay were mixed in the aramid solution with high-speed stirring for homogeneous dispersion of the clay. Thin films cast from these materials after evaporating the solvent were characterised. The morphology of nanocomposites was determined by X-ray diffraction and TEM. Results revealed the formation of delaminated and disordered intercalated clay platelets in the aramid matrix. Mechanical data indicated improvement in the tensile strength and modulus with clay loading up to 6 wt.%. The glass transition temperature increased up to 20 wt.% organoclay, suggesting better cohesion between the two phases and thermal stability augmented with increasing clay loading. The water uptake reduced gradually as a function of organoclay showing decreased permeability.

Morphology, mechanical, and thermal properties of aramid/layered silicate nanocomposite materials

Aramid-based nanocomposites were prepared by solution intercalation techniques using p-aminobenzoic acid-modified montmorillonite. Polyamide was synthesized by reacting 4,4′-oxydianiline with isophthaloyl chloride in dimethyl acetamide. To create chemical interactions between the two phases for better dispersion of organoclay, aramid chains were selectively amine end-capped. The influence of organically modified clay on the morphology was investigated by x-ray diffraction (XRD), polarized optical microscopy (POM), and transmission electron microscopy (TEM). Mechanical, thermal, and water uptake measurements were carried out to further verify other physical properties of the nanocomposites. Tensile strength, modulus, elongation at break, and toughness were improved relative to pure polymer with the addition of 6 wt% organoclay. Thermal-decomposition temperatures of the nanocomposites were in the range 300–450 °C. Water uptake of neat aramid film was rather high (5.7%) and decreased with augmenting organoclay. DSC exhibited increase in the glass transition temperature (118 °C) up to addition of 16 wt% of organoclay.

In situ reactive compatibilization of aramid/polystyrene blends using amine‐functionalized polystyrene

AbstractHigh molecular weight aramid chains (Ar) were synthesized from aromatic diamine and diacid chloride. Amine functionality was introduced to polystyrene (PS) in two steps i.e., nitration followed by reduction producing amino functional polystyrene (APS) which serves as a reactive compatibilizer, being reactive with the Ar end‐groups. APS was characterized by FTIR, NMR spectral data, and exploited in the preparation of Ar/APS blends, and the effect of reactive compatibilization on blend morphology and interfacial adhesion was explored. Two blend systems Ar/PS and Ar/APS were investigated over a range of PS or APS ratios. To assess the effect of amine units incorporated in PS, on the compatibility with Ar; morphology, thermal, and mechanical properties were probed. Incorporation of reactivity into the system has resulted in significant refinement of the blend morphology and augmentation of thermal stability. The in situ generation of APS‐g‐Ar copolymers during solution mixing of APS and Ar was evaluated using spectroscopic analysis. In addition to stabilizing the microstructure, in situ compatibilization was found to alter the mechanical properties of the Ar/APS interface. Ar/APS blend containing 10 wt% APS was found to demonstrate optimum mechanical reinforcement as complemented by the optimal thermal and morphological profiles of 10 wt% Ar/APS blend. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Inclusion of aramid chains into the layered silicates through solution intercalation route

Aramid–organoclay nanocomposites were fabricated through solution intercalation technique. Montmorillonite was modified with p-amino benzoic acid in order to have compatibility with the matrix. The effect of clay dispersion and the interaction between clay and polyamide chains on the properties of nanocomposites were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile testing of thin films, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and water uptake measurements. Excessive clay dispersion was achieved even on the addition of high proportions of clay. The structural investigations confirmed the formation of delaminated nanostructures at low clay contents and disordered intercalated morphology at higher clay loadings. The tensile behavior and thermal stability significantly amplified while permeability reduced with increasing dispersibility of organoclay in the polyamide matrix.

New aramid‐based nanocomposites: Synthesis and characterization

AbstractNew type of nanocomposites containing various proportions of montmorillonite in aromatic polyamide was prepared via solution intercalation method. Aramid chains were synthesized by reacting 4,4′‐oxydianiline with isophthaloyl chloride in N,N′‐dimethyl acetamide. Dodecylamine was used as swelling agent to change the hydrophilic nature of montmorillonite into organophilic. Appropriate amounts of organoclay were mixed in the polymer solution using high‐speed mixer for complete dispersion of the clay. Thin films cast from these materials after evaporating the solvent were characterized by XRD, TEM, mechanical, thermal, and water absorption measurements. The structure and morphology of the nanocomposites determined by XRD and TEM revealed the formation of exfoliated and intercalated clay platelets in the aramid matrix. Mechanical data indicated improvement in the tensile strength and modulus of the nanocomposites with clay loading up to 6 wt%. The glass transition temperature increased up to 12 wt% clay content and thermal stability amplified with increasing clay loading. The water absorption reduced gradually as a function of organoclay and approached to zero with 20 wt% organoclay in the aramid. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Inter-Phase Bonding in Poly(hyroxyamide)-silica Hybrids: Effect of Isocyanto‐propyltriethoxysilane Addition on the Structure and Properties

Novel aramid‐silica ceramers with increased inter‐phase bonding have been prepared via the sol‐gel process. The aramid chains with pendant alkoxy groups were synthesized by reacting poly(hyroxyaramid) chains with isocyanato‐propyltriethoxysilane (ICTOS). The sol‐gel process was carried out in this matrix after mixing an appropriate amount of tetraethoxysilane (TEOS) to produce a silica network structure chemically bonded to the matrix. The effect of ICTOS addition on morphology, thermal and mechanical properties of the composites has been studied. Properties of the composites were compared with the hybrid system where a similar matrix was used but the silica network was developed using a mixture of ICTOS and TEOS or TEOS alone. The hybrid materials in which ICTOS was added prior to TEOS in the matrix showed better mechanical and thermal properties as compared to the system in which ICTOS and TEOS were used together or where only TEOS was used in the pure aramid matrix. The glass transition temperature was found to increase and the coefficient of thermal expansion was considerably reduced in chemically bonded ceramers as compared to those having no interfacial bonding.

Preparation and Properties of Aramid-Silica Hybrids with Inter-Phase Bonding Through (3-glycidoxypropyl)-trimethoxysilane

Nano-composites from aramid-silica system have been prepared via sol-gel process. Poly (phenyleneterephthalamide) copolymer chains were prepared by reacting a mixture of p- and m-phenylenediamines with terephthaloyl chloride in dimethylacetamide used as solvent. The sol-gel process in the polymer matrix was carried out through hydrolysis and condensation of a mixture of tetraethoxysilane and (3-glycidoxypropyl) trimethoxysilane. The latter was used to develop linkage, on one hand with silica network structure using alkoxy groups and on the other hand with aramid chains at its secondary amine groups through glycidal groups of silane. Mutual interaction between the two disparate phases aramid and silica network was thus created. Thin films of the composites containing different proportions of silica ranging from 5.0 to 25.0-wt% were cast by the solvent elution technique. The α-relaxation temperature associated with the glass transition was measured by the dynamic mechanical thermal analysis. The results showed an increase in the glass transition temperature from 328°C for the pure aramid to 352°C for the hybrid materials containing 25-wt% silica, an indicative of the increased interfacial interaction between the two phases. Films having relatively low silica content were flexible and transparent, but those with high silica content were opaque and brittle. These films were tested for their tensile strength, modulus and toughness. The mechanical strength of the composites as compared to the pure aramid increased initially but with further addition of silica the strength decreased. The initial increase can be explained due to increased interfacial interaction between the two phases, however agglomeration of silica particles was responsible for decreasing strength at higher silica contents.

An investigation of novel approaches in order to provide crosslinked fully aromatic polyamide chains

Two different, novel approaches to crosslink fully aromatic, rigid-rod aramid chains were studied. First, the new rigid-rod aramid poly[1,4-phenylen-2,5-bis(prop-2-ynyloxy)-terephthalamide] with an inherent viscosity of η inh = 2.74 dL/g was synthesized by low temperature polycondensation of p-phenylendiamine and 2,5-bis(prop-2-ynyloxy)-terephthaloylchloride. The pendant alkinyl moieties allowed thermally induced crosslinking at temperatures higher than 200°C. No weight loss was found due to this treatment, but curing gave rise to the formation of stable radicals. However, no fiber spinning experiments were carried out using this material due to the insufficient stability of the polymer chains against degradation when being dissolved in sulfuric acid. Furthermore, fibers of a rigid rod polyamide containing pyrimidine moieties, produced by polycondensation of bis-silylated 2,5-diaminoprimidine and terephthaloyl dichloride, were spun from nematic solutions. Fibers were crosslinked by complexation with nickel(II)-ions in the swollen state. Both crosslinked and non-crosslinked, otherwise identically processed samples, were characterized by wide-angle X-ray diffraction (WAXD) measurements and mechanical tests. A post-spin heat treatment was employed to improve the low degrees of orientation and crystallinity that the untreated fibers in general showed. The dominating crystal structures of both fiber samples are similar to Modification II of the well characterized fibers from poly(p-phenylene-terephthalamide) (PPTA). The number and size of the morphological defects in the crosslinked fibers was significantly higher than in the non-crosslinked samples. The influence of the annealing on the mechanical fiber properties and the molecular order in the fibers was investigated. The values of all mechanical parameters were considerably lower in the case of the crosslinked fibers, probably due to the collapse of the entire supramolecular order and fiber morphology.

Interphase bonding in organic–inorganic hybrid materials using aminophenyltrimethoxysilane

Several types of silica and titania-aramid hybrid materials were prepared using a sol–gel process. The aramid chains were prepared by the reaction of a mixture of m- and p-phenylene diamines and terephthaloyl chloride in dimethylacetamide. Addition of different amounts of tetraethoxysilane and tetrapropylorthotitanate in the polymer solution, and their subsequent hydrolysis-condensation yielded silica and titania networks, respectively, in the aramid matrix. The chemical bonding between the organic and inorganic phases was achieved by end-capping the aramid chains with aminophenyltrimethoxysilane. In-situ hydrolysis/condensation of tetraethoxysilane or tetrapropylorthotitanate along with that of aminophenyl-trimethoxysilane was carried out to produce silica and titania networks chemically bonded to aramid chains. Thin transparent and tough films containing up to 20 wt% of metal oxides were prepared. The storage and the loss moduli as a function of temperature were measured using dynamic mechanical thermal analysis. A greater shift in the α-relaxation associated with the glass transition temperature ( T g ) was observed in case of chemically bonded ceramers as compared to the unbonded and has been explained in term of greater interaction between the organic and inorganic phases.

Thermal and mechanical properties of aramid-based titania hybrid composites

The sol-gel process has been used to prepare various types of aramid-titania hybrid materials. Specifically, a mixture of m- and p-phenylenediamines was reacted with terephthaloyl chloride to produce linear polyamide chains in a dimethylacetamide solvent. Various proportions of tetrapropylorthotitanate (TPOT) were added, and its subsequent hydrolysis-condensation in the polymer solution produced a titania (TiO 2 ) network in the aramid matrix. Thin films prepared from these materials were tested for their tensile strength, which was found to decrease with increasing proportions of titania. To remedy this through chemical bonding between the matrix and the inorganic network, a slight excess of terephthaloyl chloride or 1,3,5-benzenetricarbonyl chloride was added near the end of the polymerization reaction. These aramid chains were thus end-capped with single or double carbonyl chloride groups. This allowed the chains to be further modified, with aminophenyltrimethoxysilane end caps. Chemically bonding the titania network to the aramid chains was then achieved by in situ hydrolysis-condensation of TPOT along with that of aminophenyltrimethoxysilane. In this way, thin transparent and tough films could be obtained with up to 30 wt % titania. The values of the tensile strength in the case of bonded hybrid materials increased with the addition of titania, and the polyamide system with nonlinear end groupings showed larger increases than did those with the linear chains ends. The systems with linear and nonlinear aramid chain ends were able to withstand maximum tensile stresses of the order of 193 and 246 MPa, respectively. This is presumably due to the extensive bonding between the polymeric chain ends and the inorganic phases as compared to the unbonded system. The thermal decomposition temperature of these composites was found to be in the range of 500-600°C and the overall weight loss was found to be minimized in an inert atmosphere.

Preparation and properties of composites of kevlar‐nomex copolymer and boehmite

AbstractA new organic‐inorganic hybrid material was prepared by incorporating boehmite into a Kevlar‐Nomex copolymer via a sol‐gel process. Poly(phenylene‐terephthalamide) chains having aminophenyltrimethoxysilane end groups were prepared by reacting a mixture of m‐and p‐phenylenediamine with terephthaloyl chloride, followed by end‐capping with aminophenyltrimethoxysilane. The hydrolysis of the alkoxy groups of an aluminium sec‐butoxide solution in butanol was carried out in the polymer matrix, thus creating an inorganic network structure combined chemically with the aramid chains. Hybrid materials containing different proportions of boehmite in aramid were thus produced and films were cast by solvent evaporation technique. These films with up to 15 wt.‐% of boehmite were yellow and transparent, whereas the films with 20 wt.‐% or more contents of boehmite were opaque. Mechanical properties of these films were analyzed. The values of tensile strength, initial modulus, toughness and maximum strain at rupture were initially found to increase and then decrease with further addition of boehmite. The tensile modulus of the hybrid material was found to be in the range of 3.0–4.5 GPa at 25°C. These ceramers were found to withstand maximum tensile stress of the order of 252 MPa, and the thermal decomposition temperature was around 450°C. The storage modulus as measured using DMTA was in the range of 7.6–18.9 GPa. The tan δ peak which in general became broader with increasing boehmite content showed a shoulder for composites containing large amounts of boehmite. The position of the peaks shifted towards high temperature with the increase in the inorganic contents showing hindrance in motion with increasing boehmite contents.

Chemically bonded silica–polymer composites from linear and branched polyamides in a sol–gel process

A new type of polymer–silica composite based on aramids of either linear or non-linear structure has been prepared successfullyvia the sol–gel process. The linear polyamide chains were prepared by the reaction of a mixture of m-phenylene and p-phenylene diamines and terephthaloyl chloride in dimethylacetamide. The non-linear (branched) polyamide chains (having an increased number of reactive ends) were synthesized using 1,3,5-benzenetricarbonyl chloride and terephthaloyl chloride to increase the mass average functionality of the monomer. A slight excess of acid chloride was added in both cases to produce amide chains with carbonyl chloride end groups, which permitted the chains to be end-capped with aminophenyltrimethoxysilane. Addition of tetramethoxysilane to a solution of the polymer, and its subsequent hydrolysis and condensation produced a silica network phase chemically bonded to the aramid chains. Films thus produced were yellow, and transparent for concentrations of silica of up to 25 mass%. Tensile strengths increased gradually with increasing silica content up to this same concentration, but then decreased significantly. The overall values of the strength were found to be smaller for the non-linear aramid chains, relative to those of the linear, possibly because of the branches interfering with interchain interactions. Nonetheless, the increases in the tensile strength with increasing inorganic network phase were larger for the non-linear polymer, consistent with the goal of increasing the bonding between the organic and inorganic phases by increasing the number of amidophenyltrimethoxysilane chain ends. Increasing these strengths to values greater than those for the linear chains can probably be achieved by having the branched regions only near the ends of the chains. Since these transparent ceramers were found to withstand tensile stresses of the order of 175 MPa and had thermal decomposition temperatures around 460–475 °C, they may be very useful as matrices for fibre-reinforced composites.