Solvent Casting Process Research Articles

Polymer nanocomposites with cellulose nanocrystals made by co‐precipitation

ABSTRACTA premixing method to produce polymer nanocomposites with cellulose nanocrystals (CNCs) is reported. This method involves the dissolution and dispersion of a polymer and CNCs in an organic solvent, co‐precipitation into water, drying of the resulting particles, and subsequent melt processing. The key aspect of the method is that it allows the kinetic trapping of well‐dispersed CNCs in the polymer. Although the nanocomposite must be dried before subsequent melt‐processing, the organic solvent can be removed by extraction in water and recycled, leaving only residual water in the composite, which is easily eliminated. This process presents numerous advantages compared with the time‐consuming solvent casting process, which often suffers from incomplete organic solvent evaporation. As a testbed, polyurethane (PU) composites with up to 30% of CNCs were prepared. These materials were either melt‐processed as produced or used as a masterbatch, i.e., they were diluted via melt‐mixing with neat polymer toward nanocomposites with lower filler content. All nanocomposites prepared using this approach had a homogeneous appearance. They displayed similar mechanical properties as the corresponding reference materials made by solvent casting, and significantly better properties than materials prepared by direct melt mixing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45648.

PLA Nanocomposites Reinforced with Cellulose Nanocrystals from Posidonia oceanica and ZnO Nanoparticles for Packaging Application

Poly(lactic acid) (PLA) based nanocomposites reinforced with 1 wt% of surfactant-modified cellulose nanocrystals (s-CNC) extracted from Posidonia oceanica plant waste and zinc oxide nanoparticles (ZnO NPs) at different concentrations (0.1 and 0.5 wt%) were prepared by solvent casting process. Their thermal, morphological, optical, mechanical and water vapor permeability properties were investigated. Tensile testing showed increased values for strength and deformation at break in PLA based formulations reinforced with s-CNC and ZnO NPs as a consequence of better nanofiller dispersion compared to binary films reinforced only with ZnO NPs. Moreover, the effect of s-CNC and ZnO NPs provoked an improvement of barrier properties, highlighting the synergic ability of nanofillers to increase the tortuous path of gas molecules, reducing the water vapor permeability coefficients, a property of fundamental importance in food packaging applications. Finally, antimicrobial activity was evaluated using two bacterial strains, Escherichia coli and Listeria innocua.

Development and characterization of porous membranes based on kaolin/chitosan composite

Chitosan/kaolin composite porous membranes were successfully prepared by solvent casting and evaporation process. The suspensions with different concentration of kaolin and chitosan showed a Newtonian behaviour. Strong interaction between chitosan and kaolin was revealed by FTIR and thermogravimetric analysis. The effect of kaolin content on the morphology and properties of the obtained membranes was studied. It was found by SEM observation that the kaolin particles were well dispersed in the chitosan matrix generating a porous microstructure. Incorporation of kaolin particles also improved the mechanical and thermal properties of the membranes and reduced drastically the water washout of chitosan in moderate acidic medium. Owing to their porous structure, the water permeability of the composite chitosan/kaolin membrane was significantly enhanced. The better formulation of the dope suspension in the range studied was 4% chitosan and 5% kaolin in acetic acid. These membranes made from naturally occurring materials might play an important role in advanced research in water treatment and environmental science.

Polyurethane based on PLA and PCL incorporated with catechin: Structural, thermal and mechanical characterization

Catechin (Cat) was added into polyurethane (PU) based on a tri-block copolymer of poly(l-lactic acid) and poly(ε-caprolactone) (PLLA-b-PCL-b-PLLA) to improve the thermal stability of the final PU composite materials. The morphological, structural, mechanical and thermal properties of PU-Cat composites loaded with 1wt%, 3wt% and 5wt% of Cat were investigated and designed as PU-Cat1, PU-Cat3 and PU-Cat5, respectively. Homogeneous films were obtained after the solvent casting process, but the higher amount of 5wt% used in this work could not be successfully dispersed and produced some structural defects as were observed by scanning electron microscopy. Well dispersed Cat in PU-Cat1 and PU-Cat3 not only substantially improved the thermal stability due to the Cat antioxidant effect, but also allowed the crystallization of PCL and PLLA blocks in the final PU-Cat composites. Additionally, PU-Cat composite materials showed excellent stretchability for film production.

The wettability, mechanical and antimicrobial properties of polylactide/montmorillonite nanocomposite films.

The aim of this study was to evaluate the effect of the not activated (unmodified) montmorillonite (MMT) filler on the antibacterial properties of polymer nanocomposites with a biodegradable polylactide (PLA) matrix. The subject of research was selected to verify the reports on the lack of antibacterial properties of unmodified montmorillonite in nanocomposites and to investigate the potential conditions of their manufacturing which are decisive for the resulting properties. Evaluation of antibacterial and mechanical properties of both the starting materials and the obtained nanocomposites filled with layered silicates as well as the wettability of the materials, measured by a sitting drop method was made on samples in the form of a film. The results show that the surface wettability of the polymer nanocomposites did not exhibit significant change compared to the film of neat PLA. However, a significant improvement in the mechanical and antimicrobial properties of the nanocomposite films obtained in a specific solvent casting process of the nanocomposite preceded by exfoliation of the film in an ultrasonic homogenizer was demonstrated. The antibacterial activity against Gram-positive bacteria Staphylococcus aureus and Enterococcus faecalis was also observed, and, moreover, the montmorillonite-containing films revealed a zone of inhibition of bacterial growth when tested against the lactosepositive bacteria of the Enterobacteriaceae family, which are present in the waste water. The advantageous properties of the obtained PLA/MMT nanocomposites suggest that the unmodified montmorillonite may be potentially used as filler for polymer films in the packaging industry.

Quantitative Analysis of Connectivity and Conductivity in Mesoscale Multiwalled Carbon Nanotube Networks in Polymer Composites

Mesoscale networks of multiwalled carbon nanotubes (CNTs) dispersed in 50/50 PS/PPO (polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide)) are studied. Various dispersion states are formed by several processing methods such as solvent casting (SC) and extrusion (EXT) and followed by compression molding (CM), which alters the topology of the conductive CNT network. This in turn affects the measured electrical conductivity up to 9 orders of magnitude. Quantitative large-area STEM imaging of the representative topology revealed the existence of subtle differences in topology for various dispersion states. The analyses also reveal that strong localized CNT interactions during the SC process result in highly conductive inhomogeneous networks consisting of CNT clusters connected by individual CNTs embedded in the polymer matrix. This leads to a low electrical percolation threshold, so that as compared to a random network a higher local volume fraction than the overall volume fraction of CNTs is present. A dispers...

Pure titanium particle loaded nanocomposites: study on the polymer/filler interface and hMSC biocompatibility.

The integration of inorganic nanoparticles into polymer matrices allows for the modification of physical properties as well as the implementation of new features for unexplored application fields. Here, we propose the study of a new metal/polymer nanocomposite fabricated by dispersing pure Ti nanoparticles into a poly(methylmetacrilate) matrix via solvent casting process, to investigate its potential use as new biomaterial for biomedical applications. We demonstrated that Ti nanoparticles embedded in the poly(methylmetacrilate) matrix can act as reinforcing agent, not negatively influencing the biological response of human mesenchymal stem cell in terms of cytotoxicity and cell viability. As a function of relative amount and surface treatment, Ti nanoparticles may enhance mechanical strength of the composite-ranging from 31.1 ± 2.5 to 43.7 ± 0.7 MPa-also contributing to biological response in terms of adhesion and proliferation mechanisms. In particular, for 1 wt% Ti, treated Ti nanoparticles improve cell materials recognition, as confirmed by higher cell spreading-quantified in terms of cell area via image analysis-locally promoting stronger interactions at cell matrix interface. At this stage, these preliminary results suggest a promising use of pure Ti nanoparticles as filler in polymer composites for biomedical applications.

Multitask Imidazolium Salt Additives for Innovative Poly(l-lactide) Biomaterials: Morphology Control, Candida spp. Biofilm Inhibition, Human Mesenchymal Stem Cell Biocompatibility, and Skin Tolerance.

Candida species have great ability to colonize and form biofilms on medical devices, causing infections in human hosts. In this study, poly(l-lactide) films with different imidazolium salt (1-n-hexadecyl-3-methylimidazolium chloride (C16MImCl) and 1-n-hexadecyl-3-methylimidazolium methanesulfonate (C16MImMeS)) contents were prepared, using the solvent casting process. Poly(l-lactide)-imidazolium salt films were obtained with different surface morphologies (spherical and directional), and the presence of the imidazolium salt in the surface was confirmed. These films with different concentrations of the imidazolium salts C16MImCl and C16MImMeS presented antibiofilm activity against isolates of Candida tropicalis, Candida parapsilosis, and Candida albicans. The minor antibiofilm concentration assay enabled one to determine that an increasing imidazolium salt content promoted, in general, an increase in the inhibition percentage of biofilm formation. Scanning electron microscopy micrographs confirmed the effective prevention of biofilm formation on the imidazolium salt containing biomaterials. Lower concentrations of the imidazolium salts showed no cytotoxicity, and the poly(l-lactide)-imidazolium salt films presented good cell adhesion and proliferation percentages with human mesenchymal stem cells. Furthermore, no acute microscopic lesions were identified in the histopathological evaluation after contact between the films and pig ear skin. In combination with the good morphological, physicochemical, and mechanical properties, these poly(l-lactide)-based materials with imidazolium salt additives can be considered as promising biomaterials for use in the manufacturing of medical devices.

Processing of edible films based on nanoreinforced gelatinized starch

Fully biobased edible films were prepared using native potato starch plasticized with glycerol and further reinforced with catechin (Cat) and starch nanocrystals (SNC) obtained by acidic hydrolysis from waxy maize starch granules. The thermal stability of starch nanocrystals obtained at different pH was studied, resulting on a decreasing in thermal stability at higher pH values. The X-ray diffraction patterns of the plasticized reinforced materials display complete destructuration of starch by solvent casting process. Plasticized films showed lower onset degradation temperatures than non-plasticized starch film. The reduction of the inter- and intra-molecular bonds interaction within the polymer matrix due to glycerol presence leads to a decrease of the thermal stability of the whole system. On the other hand, Cat and SNC produced an increase on the thermal stability of the bionanocomposites delaying the beginning of the thermal decomposition of starch/glycerol systems of about 20 °C. The mechanical performance was also improved in the ternary bionanocomposite edible films. All the edible films were fully disintegrated in compost conditions suggesting their possible applications as biodegradable edible films for packaging.

Layered double hydroxides: Efficient fillers for waterborne nanocomposite films

Using Layered double hydroxides (LDH) nanoparticles and film-forming latexes, waterborne nanocomposite films were produced by simply a heterocoagulation and solvent casting process. Self-standing and transparent films with LDH contents from 2.5 to 15vol% were prepared. The structure, microstructure and mechanical behavior were thoroughly investigated by powder X-ray diffraction (PXRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), scanning electron microscopy (FIB–SEM) and dynamic mechanical analysis (DMA). Favorable electrostatic interactions between pristine LDH and the latex ensured a good dispersion of the bidimensional LDH platelets in the films. Above a certain content of LDH, the formation of a well-defined cellular LDH network following the starting latex morphology was observed. Such a percolating microstructure induces a large mechanical reinforcement significant of a mechanical percolation behavior.

Influence of different alkyl‐methylimidazolium tetrafluoroborate ionic liquids on the structure of pebax® films. Consequences on thermal, mechanical, and water sorption and diffusion properties

ABSTRACTIn this work, three ionic liquids (ILs) differing by the length of the alkyl chain linked to their cation were incorporated in a Pebax® copolymer matrix through a solvent cast process for composition from 0 to 70 wt % IL. The copolymer/IL miscibility was investigated via IR Spectroscopy, Differential Scanning Calorimetry and Scanning Electron Microscopy. The three ILs dissolved in the copolymer soft phase for ILs content below 30 wt % whereas they formed segregated dispersed domains at higher loadings. The plasticizing effect of the ILs was examined through DSC and thermomechanical analyses. In the range of IL amount from 0 to 30 wt %, no significant differences were observed in the thermomechanical properties as a function of the IL structure. At higher IL content, the films based on 1‐ethyl‐methylimidazolium tetrafluoroborate sustained better properties. All films exhibited a good thermal stability up to 300 °C. The water sorption isotherms were modeled with GAB equation and both the kinetic and thermodynamic parameters of the sorption mechanism were investigated. A non‐monotonic evolution of the GAB parameters and diffusion coefficient as a function of the IL content was evidenced. Moreover, different behaviors were observed as a function of the IL nature and structuration within the copolymer matrix. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 811–824

Tuning the properties of polyhydroxybutyrate films using acetic acid via solvent casting.

Biodegradable polyhydroxybutyrate (PHB) films were fabricated using acetic acid as an alternative to common solvents such as chloroform. The PHB films were prepared using a solvent casting process at temperatures ranging from 80 °C to 160 °C. The crystallinity, mechanical properties and surface morphology of the films cast at different temperatures were characterized and compared to PHB films cast using chloroform as a solvent. Results revealed that the properties of the PHB film varied considerably with solvent casting temperature. In general, samples processed with acetic acid at low temperatures had comparable mechanical properties to PHB cast using chloroform. This acetic acid based method is environmentally friendly, cost efficient and allows more flexible processing conditions and broader ranges of polymer properties than traditional methods.

Effect of constrained amorphous region on properties of acid–base polyelectrolyte membranes based on sulphonated poly(ether ether ketone) and a nonconjugated diamine

The phenomenon of polymer chains being restrained from participating in relaxation mechanisms has been discussed for a number of situations in the field of polymer science. In the present study we invoke the same as a mechanistic origin of property improvement in an acid–base polymeric membrane for fuel cell application. Sulfonated polyether ether ketone (sPEEK) and a non conjugated diamine (3, 3′ dichloro 4,4′ diaminodiphenylmethane) were used as the acid and base components, respectively to prepare the membranes by a facile solvent casting process. The ionic cross-link induced constrained amorphous region (C) in the acid–base membranes is quantified as a function of basic component loading from the relative depression in the dissipation factor, tan δ using dynamic mechanical analysis (DMA); found to be a staggering 62% at 25% basic component loading. The significantly higher C values are attributed to strong acid–base interactions as established from morphological investigations by field emission scanning electron microscopy (FESEM), FTIR studies and IEC measurements. Consequent to the existence of constrained amorphous region of reduced mobility, significant improvement in thermomechanical properties, (~5 fold increase in storage modulus, 2 fold increase in tensile strength and ~100°C increase in glass transition temperature compared to pristine sPEEK) thermal, dimensional as well as oxidative stability, of the acid–base membranes are observed compared to the pristine SPEEK membrane. We envisage that the hitherto unexplored acid–base membranes derived from an acidic polymer and a small molecule non-conjugated diamine can also be suitable candidates for fuel cell applications. In addition these fundamental studies are expected to provide insights into mechanistic origins of the property improvements in acid–base membranes.

Mechanical properties of Gelatin –Hydroxyapatite composite for bone tissue engineering

In this study, hydroxyapatite (HAp) and gelatin (GEL) scaffolds were prepared to mimic the mineral and organic component of natural bone. The raw material was first compounded and resulting composite were molded into the petridishes. Using Solvent casting process, it is possible to produce scaffolds with mechanical and structural properties close to natural trabecular bone.The mechanical properties of composites were investigated by Thermo-mechanical analyzer (TMA), Vickers microhardness tester, Universal testing machine. It was observed that the composite has maximum tensile strength of 37.13MPa ( oven drying) and % elongation of 7.68 (Oven drying) and 2.04 (Natural drying) at 15% of Hap respectively. These results demonstrate that the prepared composite scaffold is a potential candidate for bone tissue engineering.Bangladesh J. Sci. Ind. Res. 50(1), 15-20, 2015

Influence of functionalized halloysite clays (HNT) on selected properties of multiblock (e)PBS-EG copolymer obtained by enzymatic catalysis

In this paper, we discuss the functionalization of halloysite aluminosilicate clays (HNT) with anionic surfactant – sodium dodecanoate (NaL) and their use in new polymeric nanocomposites preparation via solvent casting. The selected polymer matrix were segmented; copoly(ester-ether)s – poly(butylene succinate-co-ethylene glycol) (PBS-EG) were synthesized for the first time with the use of enzymatic catalyst from Candida antarctica lipase B. The influence of variable concentration of NaL, temperature, and time on functionalization and finally on the chemical structure (IR) and colloidal stability (zeta potential) of functionalized HNT (f-HNT) was examined. Nanocomposites were prepared via solvent casting process, where 1 wt% of HNTs and 1 wt% of f-HNT clays were added to the (e)PBS-EG solution in chloroform. The chemical structure, topography, and hydrophilic/hydrophobic properties of prepared nanocomposites were determined by nuclear magnetic resonance (1H NMR), infrared spectroscopy (IR), scanning electron microscopy, and water contact angle. It was observed that higher concentration of NaL, longer modification time, and higher temperature lead to even distribution of f-HNT into (e)PBS-EG matrix. Halloysite clays in general improved the hydrophilicity of (e)PBS-EG and f-HNT was found to act as nucleating agent during polymer crystallization.

Preparation and properties of poly(vinyl alcohol)/chitosan blend bio-nanocomposites reinforced by cellulose nanocrystals

The aim of this paper is to report the effect of the addition of cellulose nanocrystals (CNCs) on the mechanical, thermal and barrier properties of poly(vinyl alcohol)/chitosan (PVA/Cs) bio-nanocomposites films prepared through the solvent casting process. The characterizations of PVA/Cs/CNCs films were carried out in terms of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA and DTG), oxygen transmission rate (OTR), and tensile tests. TEM and SEM results showed that at low loading levels, CNCs were dispersed homogenously in the PVA/Cs matrix. The tensile strength and modulus in films increased from 55.1 MPa to 98.4 MPa and from 395 MPa to 690 MPa respectively, when CNCs content went from 0 wt% to 1.0 wt%. The thermal stability and oxygen barrier properties of PVA/Cs matrix were best enhanced at 1.0 wt% of CNCs loading. The enhanced properties attained by incorporating CNCs can be beneficial in various applications.

Simulation analysis of drying of ternary polymeric solution coatings

A simulation study on multicomponent polymeric solvent casting process was carried out using known different models and their relative performance of the model assessed in terms of residual parameters and solvent concentration profiles in the coating film. While all the models were found to predict nearly identical concentration profile for highly volatile solvents, significant variation in the profiles was observed in case of the less volatile solvents. Estimated values of the preexponential factors (D01 and D02) exhibited marginal differences implying perhaps a material balance deviation of the predictive models. The effect of air flow rate used for the drying process has been realized through its influence on the skinning behavior, low flow rate being the preferred while for maintaining the appropriate level of skinning.

A novel electronic nose based on porous In2O3 microtubes sensor array for the discrimination of VOCs

We have innovatively developed an electronic nose consisting of only one type of semiconductor metal oxide (SMO) material. The representative SMO material, porous In2O3 microtubes in this work, offered great surface area and large gas penetration channels. By using a solvent casting process, different amounts of porous In2O3 microtubes were coated on Al2O3 substrate, forming a resistometric SMO sensor array-based electronic nose. Each sensing unit in the electronic nose exhibited independent response toward ethanol. We have successfully applied this electronic nose to distinguish four alcohols at the same concentrations (100ppm), and also utilized the electronic nose for the discrimination of 14 volatile organic compounds (VOCs). Clear differentiation among all the 14 VOCs both at their immediately dangerous to life or health (IDLH) and the permissible exposure limit (PEL) concentrations has been achieved with no errors or misclassifications. We expect that this method will expand the application of SMO sensor array-based electronic nose which has been largely limited by the selection of commercially available SMOs and dopants.

Massive electrical conductivity enhancement of multilayer graphene/polystyrene composites using a nonconductive filler.

We report a massive increase in the electrical conductivity of a multilayer graphene (MLG)/polystyrene composite following the addition of nonconducting silica nanoparticles. The nonconducting filler acts as a highly effective dispersion aid, preventing the sheetlike MLG from restacking or agglomerating during the solvent casting process used to fabricate the composite. The enhanced dispersion of the MLG leads to orders of magnitude enhancement in electrical conductivity compared to samples without this filler.

The comparison between the effects of solvent casting and melt intercalation mixing processes on different characteristics of polylactide‐nanographite platelets composites

This study investigates the influence of enhanced dispersion of nanographite platelets (NGP) fillers through solvent casting mixing process on rheological, electrical and thermal properties of polylactide (PLA)/NGP composites. PLA/NGP composites were fabricated at 1 to 5 wt% filler contents by means of three processing techniques: (i) dry mixing and melt intercalation; (ii) solvent casting using dichloromethane organic solvent; and (iii) combination of solvent casting and melt intercalation techniques. The extent of dispersion of nanofillers within polymer matrix was evaluated through X‐ray diffraction and transmission electron microscopy analysis of the composites. Morphological studies of the samples revealed that the maximum extent of dispersion of NGP fillers within PLA matrix was achieved when the combination of solvent casting and melt intercalation processes occurred. Rheological analyses of the samples were indicative of deterioration in the composites produced through solvent casting mixing process. Despite of initial reduction in electrical resistivity of the composites after the addition of 1 wt% of NGP fillers, further addition of nanofillers did not exhibit a considerable enhancement in their electrical conductivity of the composites. Thermogravimetric analysis of the composites was demonstrative of enhancing impact of nanofiller loading, along with detrimental effect of solvent casting on the thermal stability of the PLA matrix. POLYM. ENG. SCI., 55:1560–1570, 2015. © 2014 Society of Plastics Engineers