Influence of specific intermolecular interactions on the thermal and dielectric properties of bulk polymers: atomistic molecular dynamics simulations of Nylon 6.

Specific intermolecular interactions, in particular H-bonding, have a strong influence on the structural, thermal and relaxation characteristics of polymers. We report here the results of molecular dynamics simulations of Nylon 6 which provides an excellent example for the investigation of such an influence. To demonstrate the effect of proper accounting for H-bonding on bulk polymer properties, the AMBER99sb force field is used with two different parametrization approaches leading to two different sets of partial atomic charges. The simulations allowed the study of the thermal and dielectric properties in a wide range of temperatures and cooling rates. The feasibility of the use of the three methods for the estimation of the glass transition temperature not only from the temperature dependence of structural characteristics such as density, but also by using the electrostatic energy and dielectric constant is demonstrated. The values of glass transition temperatures obtained at different cooling rates are practically the same for the three methods. By proper accounting for partial charges in the simulations, a reasonable agreement between the results of our simulations and experimental data for the density, thermal expansion coefficient, static dielectric constant and activation energy of γ and ß relaxations is obtained demonstrating the validity of the modeling approach reported.

Molecular dynamics simulations of uniaxial deformation of thermoplastic polyimides.

The results of atomistic molecular-dynamics simulations of mechanical properties of heterocyclic polymer subjected to uniaxial deformation are reported. A new amorphous thermoplastic polyimide R-BAPO with a repeat unit consisting of dianhydride 1,3-bis-(3',4,-dicarboxyphenoxy)diphenyl (dianhydride R) and diamine 4,4'-bis-(4''-aminophenoxy)diphenyloxide (diamine BAPO) was chosen for the simulations. Our primary goal was to establish the impact of various factors (sample preparation method, molecular mass, and cooling and deformation rates) on the elasticity modulus. In particular, we found that the elasticity modulus was only slightly affected by the degree of equilibration, the molecular mass and the size of the simulation box. This is most likely due to the fact that the main contribution to the elasticity modulus is from processes on scales smaller than the entanglement length. Essentially, our simulations reproduce the logarithmic dependence of the elasticity modulus on cooling and deformation rates, which is normally observed in experiments. With the use of the temperature dependence analysis of the elasticity modulus we determined the flow temperature of R-BAPO to be 580 K in line with the experimental data available. Furthermore, we found that the application of high external pressure to the polymer sample during uniaxial deformation can improve the mechanical properties of the polyimide. Overall, the results of our simulations clearly demonstrate that atomistic molecular-dynamics simulations represent a powerful and accurate tool for studying the mechanical properties of heterocyclic polymers and can therefore be useful for the virtual design of new materials, thereby supporting cost-effective synthesis and experimental research.

PLGA/Ag nanocomposites: in vitro degradation study and silver ion release.

New nanocomposite films based on a biodegradable poly (DL-Lactide-co-Glycolide) copolymer (PLGA) and different concentration of silver nanoparticles (Ag) were developed by solvent casting. In vitro degradation studies of PLGA/Ag nanocomposites were conducted under physiological conditions, over a 5 week period, and compared to the behaviour of the neat polymer. Furthermore the silver ions (Ag(+)) release upon degradation was monitored to obtain information on the properties of the nanocomposites during the incubation. The obtained results suggest that the PLGA film morphology can be modified introducing a small percentage of silver nanoparticles that do not affect the degradation mechanism of PLGA polymer in the nanocomposite. However results clearly evinced the stabilizing effect of the Ag nanoparticles in the PLGA polymer and the mineralization process induced by the combined effect of silver and nanocomposite surface topography. The Ag(+) release can be controlled by the polymer degradation processes, evidencing a prolonged antibacterial effect.

Micropatterned hydrogenated amorphous carbon guides mesenchymal stem cells towards neuronal differentiation.

This study investigated how the design of surface topography may stimulate stem cell differentiation towards a neural lineage. To this end, hydrogenated amorphous carbon (a-C:H) groove topographies with width/spacing ridges ranging from 80/40µm, 40/30µm and 30/20µm and depth of 24 nm were used as a single mechanotransducer stimulus to generate neural cells from human bone marrow mesenchymal stem cells (hBM-MSCs) in vitro. As comparative experiments, soluble brain-derived neurotrophic factor (BDNF) was used as additional biochemical inducer agent. Despite simultaneous presence of a-C:H micropatterned nanoridges and soluble BDNF resulted in the highest percentage of neuronal-like differentiated cells our findings demonstrate that the surface topography with micropatterned nanoridge width/spacing of 40/30µm (single stimulus) induced hBM-MSCs to acquire neuronal characteristics in the absence of differentiating agents. On the other hand, the alternative a-C:H ridge dimensions tested failed to induce stem cell differentiation towards neuronal properties, thereby suggesting the occurrence of a mechanotransducer effect exerted by optimal nano/microstructure dimensions on the hBM-MSCs responses.

Nanofibrillar self-organization of regioregular poly(3-hexylthiophene) and [6,6]-phenyl C(61)-butyric acid methyl ester by dip-coating: a simple method to obtain efficient bulk heterojunction solar cells.

In this paper the dip-coating technique has been investigated as a method for the production of regioregular poly(3-hexylthiophene) (RR-P3HT):[6,6]-phenyl C(61)-butyric acid methyl ester (PCBM)-based solar cells. We found that the utilization of the dip-coating technique for the RR-P3HT:PCBM system can facilitate its self-assembly into a nanofibrillar lamellar structure after evaporation of the solvent. The condition for the formation of the nanofibrillar structures leads to a power conversion efficiency of 3.6% by using only this approach without thermal treatment.

Valorization and extraction of cellulose nanocrystals from North African grass: Ampelodesmos mauritanicus (Diss).

The aim of this research activity was based on the revalorization of Amplodesmos mauritanicus (Diss), an African grass largely presented in the Algerian territory. Diss stems were selected as native botanic material for the extraction of cellulose nanocrystals (CNC). Two different pretreatment steps were carried out to extract CNC from Amplodesmos mauritanicus stems and the following acidic hydrolysis procedure allowed to extract/obtain cellulose nanocrystals in aqueous suspension. The effect of the two different pretreatments, based essentially on chemical or enzymatic treatments, were deeply investigated and the properties compared. Field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were considered for the characterization of raw material, chemical or enzymatic treated Diss stems and CNC extracted from both chemical and enzymatic pretreated cellulose.

Polyvinyl alcohol/chitosan hydrogels with enhanced antioxidant and antibacterial properties induced by lignin nanoparticles.

Polyvinyl alcohol/chitosan (PVA/Ch) hydrogels containing 1 and 3wt% of lignin nanoparticles (LNPs) were prepared through a freezing-thaw procedure. Results from microstructural, thermal and mechanical characterization of LNPs based PVA/Ch demonstrated that the lowest amount of LNPs (1wt%) was beneficial, whereas the presence of agglomerates at higher LNP content limited the effect. Moreover, a different swelling behaviour was observed for hydrogels containing LNPs with respect of PVA/Ch, due to the formation of a porous honeycomb-like structure. A synergic effect of Ch and LNPs was revealed in terms of antioxidative response by DPPH (1,1-Diphenyl-2-picryl-hydrazyl) activity of migrated substances, whereas results from antimicrobial tests confirmed LNPs as effective against Gram negative bacteria (E. coli) when compared to Gram positive (S.aureus and S. epidermidis) strains. The obtained results suggested the possible use of produced PVA/Ch hydrogels incorporating LNPs in many different sectors, such as drug delivery, food packaging, wound dressing.

Cellulose nanocrystals as templates for cetyltrimethylammonium bromide mediated synthesis of Ag nanoparticles and their novel use in PLA films.

In the present paper, we reported how cellulose nanocrystals (CNC) from microcrystalline cellulose have the capacity to assist in the synthesis of metallic nanoparticles chains. A cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used as modifier for CNC surface. Silver nanoparticles were synthesized on CNC, and nanoparticle density and size were optimized by varying concentrations of nitrate and reducing agents, and the reduction time. The experimental conditions were optimized for the synthesis and the resulting Ag grafted CNC (Ag-g-CNC) were characterized by means of TGA, SEM, FTIR and XRD, and then introduced in PLA matrix. PLA nanocomposite containing silver grafted cellulose nanocrystals (PLA/0.5Ag-g-1CNC) was characterized by optical and thermal analyses and the obtained data were compared with results from PLA nanocomposites containing 1% wt. of CNC (PLA/1CNC), 0.5% wt. of silver nanoparticles (PLA/0.5Ag) and hybrid system containing CNC and silver in the same amount (PLA/1CNC/0.5Ag). The results demonstrated that grafting of silver nanoparticles on CNC positively affected the thermal degradation process and cold crystallization processes of PLA matrix. Finally, the antibacterial activity of the different systems was studied at various incubation times and temperatures, showing the best performance for PLA/1CNC/0.5Ag based nanocomposite.

Effect of cellulose and lignin on disintegration, antimicrobial and antioxidant properties of PLA active films.

This study reports the effects on antimicrobial, antioxidant, migration and disintegrability activities of ternary nanocomposite films based on poly(lactic acid) incorporating two biobased nanofillers, (cellulose nanocrystals (CNC) and lignin nanoparticles (LNP)), in two different amounts (1 and 3% wt.). Results from antimicrobial tests revealed a capacity to inhibit the Gram negative bacterial growth of Xanthomonas axonopodis pv. vesicatoria and Xanthomonas arboricola pv. pruni along the time, offering innovative opportunities against dangerous bacterial plant pathogens. LNP proved to be highly efficient in antioxidation activity, based on the disappearance of the absorption band at 517nm of the free radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH) upon reduction by an antiradical compound; moreover the combination of LNP and CNC generates a synergistic positive effect in the antioxidation response of PLA ternary films. Furthermore, all the studied formulations showed a disintegrability value up to 90% after 15days of incubation in composting conditions. Migration results showed that the films can be considered suitable for application in food packaging field.

Revalorization of sunflower stalks as novel sources of cellulose nanofibrils and nanocrystals and their effect on wheat gluten bionanocomposite properties.

Novel gluten based bionanocomposites reinforced with cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) extracted from sunflower stalks by respectively a steam explosion treatment and a hydrolysis procedure, were prepared by casting/evaporation. The extracted cellulose nanomaterials, both CNC and CNF, were embedded in gluten matrix and their effect was investigated. Morphological investigations highlighted that gluten based bionanocomposites showed a homogenous morphology, the absence of visible cellulose nanoreinforcements, and the presence of holes for Gluten_CNF nanocomposites. Gluten_CNF showed a reduction of water vapour permeability coefficients but the values are higher respect to gluten reinforced with CNC. This behaviour could be related to the ability of CNC to increase the tortuous path of gas molecules. Moreover, the results from thermal, mechanical and barrier properties confirmed the strong interactions obtained between CNC and gluten matrix during the process. The study suggested the possibility to re-valorise agricultural wastes with potential applications as reinforcement in polymer matrix bionanocomposites.

Bionanocomposite films based on plasticized PLA-PHB/cellulose nanocrystal blends.

Optically transparent plasticized poly(lactic acid) (PLA) based bionanocomposite films intended for food packaging were prepared by melt blending. Materials were plasticized with 15wt% of acetyl(tributyl citrate) (ATBC) to improve the material processability and to obtain flexibile films. Poly(hydroxybutyrate) (PHB) was used to increase PLA crystallinity. The thermal stability of the PLA-PHB blends was improved by the addition of 5 wt% of cellulose nanocrystals (CNC) or modified cellulose nanocrystals (CNCs) synthesized from microcrystalline cellulose. The combination of ATBC and cellulose nanocrystals, mainly the better dispersed CNCs, improved the interaction between PLA and PHB. Thus, an improvement on the oxygen barrier and stretchability was achieved in PLA-PHB-CNCs-ATBC which also displayed somewhat UV light blocking effect. All bionanocomposite films presented appropriate disintegration in compost suggesting their possible applications as biodegradable packaging materials.

Keratins extracted from Merino wool and Brown Alpaca fibres: thermal, mechanical and biological properties of PLLA based biocomposites.

Keratins extracted from Merino wool (KM) and Brown Alpaca fibres (KA) by sulphitolysis and commercial hydrolyzed keratins (KH) were used as fillers in poly(l-lactic) acid based biocomposites processed by solvent casting in chloroform. Different contents (1 wt.% and 5 wt.%) of keratins were considered and the morphological, thermal, mechanical, chemical and biological behaviours of the developed PLLA biocomposites were investigated. The results confirmed that surface morphologies of biocomposites revealed specific round-like surface topography function of different microsized keratin particles in different weight contents, such as the analysis of bulk morphologies which confirmed a phase adhesion strictly dependent by the keratin source. Transparency and thermal responses were deeply affected by the presence of the different keratins and their interaction with the PLLA matrix. Tensile test results underlined the possibility to modulate the mechanical behaviour of PLLA selecting the keratin type and content in order to influence positively the elastic and/or plastic response. It was demonstrated that surface characteristics of PLLA/KA systems also influenced the bovine serum albumin adsorption, moreover PLLA and PLLA biocomposites based on different kinds of keratins supported the culture of human bone-marrow mesenchymal stem cells, indicating that these biocomposites could be useful materials for medical applications.

Spin coated cellulose nanocrystal/silver nanoparticle films.

In this study, thin films of cellulose nanocrystals (CNC) and silver nanoparticles (Ag) were assembled on different substrates by spin coating. The effect of substrates, deposition parameters, and nanocrystal modification on the topographical and hydrophilic properties of the obtained layers was investigated. Dilute concentrations of pristine cellulose nanocrystals (CNC) and surfactant modified crystals (s-CNC) were used in order to evaluate the effect of modification and concentration on the uniformity of the spin coated cellulose/silver layers. Morphological investigations by field emission scanning electron microscopy and atomic force microscopy were performed in order to prove the uniformity of the obtained films, while the wettability of different surfaces were studied and correlated to the cellulose modification and content. The ability of s-CNC to form a stable dispersion in chloroform permits the formation of a uniform cellulose film on the substrate surfaces generating regular films during the spin coating process. Topographical investigations show, on the other hand, that the CNC/Ag suspension produces a non-uniform distribution. These effects can be mainly attributed to the surfactant action rather than to the chemical and electrical properties of the substrate surface. Finally, contact angle studies, underline the hydrophilic nature of s-CNC/Ag based films highlighting that the wettability properties are strongly influenced by the cellulose nanocrystal nature.

PVA bio-nanocomposites: a new take-off using cellulose nanocrystals and PLGA nanoparticles.

The formation of a new generation of hybrid bio-nanocomposites is reported: these are intended at modulating the mechanical, thermal and biocompatibility properties of the poly(vinyl alcohol) (PVA) by the combination of cellulose nanocrystals (CNC) and poly (D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs) loaded with bovine serum albumin fluorescein isothiocynate conjugate (FITC-BSA). CNC were synthesized from microcrystalline cellulose by hydrolysis, while PLGA nanoparticles were produced by a double emulsion with subsequent solvent evaporation. Firstly, binary bio-nanocomposites with different CNC amounts were developed in order to select the right content of CNC. Next, ternary PVA/CNC/NPs bio-nanocomposites were developed. The addition of CNC increased the elongation properties without compromising the other mechanical responses. Thermal analysis underlined the nucleation effect of the synergic presence of cellulose and nanoparticles. Remarkably, bio-nanocomposite films are suitable to vehiculate biopolymeric nanoparticles to adult bone marrow mesenchymal stem cells successfully, thus representing a new tool for drug delivery strategies.

Multifunctional PLA-PHB/cellulose nanocrystal films: processing, structural and thermal properties.

Cellulose nanocrystals (CNCs) synthesized from microcrystalline cellulose by acid hydrolysis were added into poly(lactic acid)-poly(hydroxybutyrate) (PLA-PHB) blends to improve the final properties of the multifunctional systems. CNC were also modified with a surfactant (CNCs) to increase the interfacial adhesion in the systems maintaining the thermal stability. Firstly, masterbatch pellets were obtained for each formulation to improve the dispersion of the cellulose structures in the PLA-PHB and then nanocomposite films were processed. The thermal stability as well as the morphological and structural properties of nanocomposites was investigated. While PHB increased the PLA crystallinity due to its nucleation effect, well dispersed CNC and CNCs not only increased the crystallinity but also improved the processability, the thermal stability and the interaction between both polymers especially in the case of the modified CNCs based PLA-PHB formulation. Likewise, CNCs were better dispersed in PLA-CNCs and PLA-PHB-CNCs, than CNC.

Nano-biocomposite films with modified cellulose nanocrystals and synthesized silver nanoparticles.

Ternary nano-biocomposite films based on poly(lactic acid) (PLA) with modified cellulose nanocrystals (s-CNC) and synthesized silver nanoparticles (Ag) have been prepared and characterized. The functionalization of the CNC surface with an acid phosphate ester of ethoxylated nonylphenol favoured its dispersion in the PLA matrix. The positive effects of the addition of cellulose and silver on the PLA barrier properties were confirmed by reductions in the water permeability (WVP) and oxygen transmission rate (OTR) of the films tested. The migration level of all nano-biocomposites in contact with food simulants were below the permitted limits in both non-polar and polar simulants. PLA nano-biocomposites showed a significant antibacterial activity influenced by the Ag content, while composting tests showed that the materials were visibly disintegrated after 15 days with the ternary systems showing the highest rate of disintegration under composting conditions.

Production of nanocrystalline cellulose from lignocellulosic biomass: technology and applications.

The use of renewables materials for industrial applications is becoming impellent due to the increasing demand of alternatives to scarce and unrenewable petroleum supplies. In this regard, nanocrystalline cellulose, NCC, derived from cellulose, the most abundant biopolymer, is one of the most promising materials. NCC has unique features, interesting for the development of new materials: the abundance of the source cellulose, its renewability and environmentally benign nature, its mechanical properties and its nano-scaled dimensions open a wide range of possible properties to be discovered. One of the most promising uses of NCC is in polymer matrix nanocomposites, because it can provide a significant reinforcement. This review provides an overview on this emerging nanomaterial, focusing on extraction procedures, especially from lignocellulosic biomass, and on technological developments and applications of NCC-based materials. Challenges and future opportunities of NCC-based materials will be are discussed as well as obstacles remaining for their large use.

Binary PVA bio-nanocomposites containing cellulose nanocrystals extracted from different natural sources: part I.

PVA bio-nanocomposites reinforced with cellulose nanocrystals (CNC) extracted from commercial microcrystalline cellulose (MCC) and from two types of natural fibres, Phormium tenax and Flax of the Belinka variety, were produced by solvent casting in water. Morphological, thermal, mechanical and transparency properties were studied while the respective efficiency of the extraction process of CNC from the three sources was evaluated. The effect of CNC types and content on PVA properties and water absorption capacity were also evaluated. Natural fibres offered higher levels of extraction efficiency when compared with MCC hydrolysis yield. Thermal analysis proved that CNC promotes the crystallization of the PVA matrix, while improving its plastic response. It was also clarified that all PVA/CNC systems remain transparent due to CNC dispersion at the nanoscale, while being all saturated after the first 18-24h of water absorption.

Ternary PVA nanocomposites containing cellulose nanocrystals from different sources and silver particles: part II.

Cellulose nanocrystals (CNC) extracted from three different sources, namely flax, phormium, and commercial microcrystalline cellulose (MCC) have been used in a polyvinyl alcohol (PVA) matrix to produce anti-bacterial films using two different amounts of silver nanoparticles (0.1 wt% and 0.5 wt%). In general, CNC confer an effect of reinforcement to PVA film, the best values of stiffness being offered by composites produced using phormium fibres, whilst for strength those produced using flax are slightly superior. This was obtained without inducing any particular modification in transition temperatures and in the thermal degradation patterns. As regards antibacterial properties, systems with CNC from flax proved slightly better than those with CNC from phormium and substantially better than those including commercial MCC. Dynamic mechanical thermal analysis (DMTA) has only been performed on the ternary composite containing 0.1 wt% Ag, which yielded higher values of Young's modulus, and as a whole confirmed the above results.