Use Of Polymers Research Articles

Influence of natural fibers on the mechanical properties and biodegradation of poly(lactic acid) and poly(ε‐caprolactone) composites: A review

AbstractThis article highlights developments in viable poly(lactic acid) (PLA) and poly(ε‐caprolactone) (PCL) ecofriendly products with enhanced mechanical properties and biodegradation based on natural resources for both reinforcements and matrices. In recent times, several techniques have emerged with emphasis on enhancing mechanical, biological, and chemical properties equivalent to or superior to conventional polymers in use. Chemical and physical modifications of the fibers and in some cases polymer matrix or both are used to obtain properties suitable for the intended application. The mechanical properties and biodegradation of PLA and PCL natural fiber composites were enhanced by the treated fibers. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Coating carbon fibres with hybrid polymers for use at high temperatures

A thermal resistance coating of different high temperature resistance polymers, e.g. polysilazane and polysiloxane was applied to a carbon roving by a continuous dip coating method. Improved mechanical and thermal resistance properties of the coated carbon roving were evaluated by thermogravimetric analysis and tensile property testing under thermal stress. Investigation of the mechanical properties of coated carbon roving revealed a significant increase in their breaking strength, which amounted to more than 50% as compared to uncoated roving. The thermal stability as well as the oxidation protection of the coated sample in ambient air at temperatures up to 800℃ was much higher than that of the control sample. Topographical phenomena occurring due to the coating on the microscale were examined by scanning electron microscopy and energy dispersive X-ray analysis. The surface energy and the adhesion property of the coated substrate were determined by measuring the contact angle.

Preparation of Al, Ti, Zr-perfluoroheptanoate compounds and their use in ring opening polymerization

Aluminum, titanium and zirconium perfluoroheptanoate (PFH) were prepared by reaction of Al, Ti and Zr-alkoxides with perfluoroheptanoic acid (PFHA) in alcohol. All compounds were characterized by NMR spectroscopy, FTIR, MS and elemental analysis and used in polymerization of 3-glycidyloxypropyltrimethoxysilane (GPTS) in order to see their catalytic activity over epoxides. These catalysts were effective in ring opening of epoxide. Poly-GPTS was characterized by 1H, 13C NMR and gel permeation chromatography (GPC).

Design and Characterization of a Silk-Fibroin-Based Drug Delivery Platform Using Naproxen as a Model Drug

The objective of this proof-of-concept study was to develop a platform for controlled drug delivery based on silk fibroin (SF) and to explore the feasibility of using SF in oral drug delivery. The SF-containing matrixes were prepared via spray-drying and film casting, and the release profile of the model drug naproxen sodium was evaluated. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR) has been used to observe conformational changes in SF- and drug-containing compositions. SF-based films, spray-dried microparticles, and matrixes loaded with naproxen were prepared. Both FTIR spectra and in vitro dissolution data demonstrated that SF β-sheet conformation regulates the release profile of naproxen. The controlled release characteristics of the SF-containing compositions were evaluated as a function of SF concentration, temperature, and exposure to dehydrating solvents. The results suggest that SF may be an attractive polymer for use in controlled drug delivery systems.

A first principles approach to identifying polymers for use in two-phase partitioning bioreactors

BACKGROUND: Two-phase partitioning bioreactors (TPPBs) employ an immiscible phase to partition toxic substrates/products to/away from cells to reduce cytotoxicity and improve bioprocess performance. Initially, immiscible organic solvents were used as the sequestering phase, and their selection included consideration of solute–solvent affinity, which can be predicted through first principles consideration of solute activity and phase equilibrium thermodynamics. Polymers can replace organic solvents in such systems, however, their selection has largely been via heuristic means, and a more fundamental approach is necessary for future success in rational polymer identification. RESULTS: Material properties (polymer crystallinity, solubility parameter, and glass transition temperature Tg) were examined across several polymers and polyaromatic hydrocarbons as target solutes. All were shown to influence solute–polymer affinity. CONCLUSION: This first attempt at identifying physical/chemical properties that affect solute–polymer partitioning has been able to demonstrate some clear trends, and has allowed us to formulate a polymer selection guide, based on first principles, to facilitate the selection of solute–polymer pairs for solid–liquid TPPB applications. Copyright © 2012 Society of Chemical Industry

RENEWABLE FIBERS AND BIO-BASED MATERIALS FOR PACKAGING APPLICATIONS – A REVIEW OF RECENT DEVELOPMENTS

This review describes the state-of-the-art of material derived from the forest sector with respect to its potential for use in the packaging industry. Some innovative approaches are highlighted. The aim is to cover recent developments and key challenges for successful introduction of renewable materials in the packaging market. The covered subjects are renewable fibers and bio-based polymers for use in bioplastics or as coatings for paper-based packaging materials. Current market sizes and forecasts are also presented. Competitive mechanical, thermal, and barrier properties along with material availability and ease of processing are identified as fundamental issues for sustainable utilization of renewable materials.

Renewable fibers and bio-based materials for packaging applications – A review of recent developments

This review describes the state-of-the-art of material derived from the forest sector with respect to its potential for use in the packaging industry. Some innovative approaches are highlighted. The aim is to cover recent developments and key challenges for successful introduction of renewable materials in the packaging market. The covered subjects are renewable fibers and bio-based polymers for use in bioplastics or as coatings for paper-based packaging materials. Current market sizes and forecasts are also presented. Competitive mechanical, thermal, and barrier properties along with material availability and ease of processing are identified as fundamental issues for sustainable utilization of renewable materials.

Synthesis of Nano-Sized Conducting Polymers for Use in Coating Layer of Disordered Carbons

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Bilayer heterojunction polymer solar cells using unsubstituted polythiophene via oxidative chemical vapor deposition

We demonstrate the use of a vacuum-based, vapor phase technique for the deposition of a donor polymer for use in polymer solar cells. Unsubstituted polythiophene (PT), which is insoluble and infusible and thus typically difficult to process, is easily prepared by oxidative chemical vapor deposition (oCVD). The oCVD process results in a conductive PT film that is heavily doped with FeCl3, which is used as the oxidizing agent. A post-deposition methanol rinse sufficiently dedopes the film and removes spent oxidant, leaving semiconducting PT with an optical bandgap close to 2eV. Drastic changes in the film color, absorption spectra, and film composition confirm the dedoping process. The resulting semiconducting PT is then applied as an electron donor in bilayer heterojunction solar cells with a thermally evaporated C60 electron acceptor layer, resulting in power conversion efficiencies up to 0.8%. The absorption edge of the PT at ∼620nm closely matches the edge present in the external quantum efficiency spectra, indicating that the oCVD PT contributes to the photocurrent of the devices. This demonstrates that the oCVD technique can be used in the processing and design of polymer active layers for polymer solar cells and hybrid small molecular organic solar cells without solubility, temperature, or substrate considerations.

Synthesis of a Novel Fused Thiophene‐thieno[3,2‐b]thiophene‐thiophene Donor Monomer and Co‐polymer for Use in OPV and OFETs

The synthesis of a novel fused hexacyclic electron rich monomer incorporating thieno[3,2-b]thiophene is reported and characterized by single crystal X-ray diffraction. Suzuki co-polymerization with benzothiadiazole (BT) afforded a novel low band-gap polymer P4TBT with high molecular weights and good solution processability. Bulk heterojunction solar cell devices using the P4TBT and [70]PCBM gave power conversion efficiencies of 2.5%. Top-gate, bottom-contact field effect transistors (FETs) using P4TBT displayed high hole mobilities of 0.07 cm(2) · Vs(-1) demonstrating the suitability of the novel monomer and polymer for use in high performing organic electronic devices.

Copoly(1,3,4-oxadiazole-naphthylimide)s containing siloxane units in the main chain: synthesis and properties

This study was concerned with the synthesis and properties of new soluble copolyimides containing naphthalene, oxadiazole and tetramethyldisiloxane units. These copolyimides were prepared by two-step polycondensation reaction in solution of aromatic diamines containing preformed oxadiazole ring with a mixture 1 : 1 of naphthalene tetracarboxylic dianhydride and tetramethyldisiloxane- [1,3-bis(4′-phthalic anhydride)]. The structure of these polymers was confirmed by Fourier transform infrared and 1 H-NMR spectroscopy. The solubility, thermal stability and glass transition temperature of these copolyimides were measured and compared with those of related polyimides which do not contain siloxane groups. All these polymers emitted an intense blue color light upon irradiation with UV light. These copoly(oxadiazole-naphthylimide)s could be considered promising candidates for organo-soluble high-performance polymers for use in novel technological applications.

Crystallization Morphology and Behavior of Polypropylene Composites Containing Microencapsulated Flame Retardant

With shells of melamine-formaldehyde (MF), urea-melamine-formaldehyde (UMF), or poly(vinyl alcohol)-melamine-formaldehyde (VMF), microencapsulated ammonium polyphosphate (APP) was prepared by in-situ polymerization for use as a flame retardant in polypropylene (PP). Microencapsulated APP showed rougher surface, smaller size, and narrower size distribution compared with APP. The results of polarized optical microscopy (POM) showed that the additives resulted in a decrease of the spherulite size and less perfection in crystal geometry of PP composites. Due to the interaction and alignment of the PP polymer chains at the surface, the surface modification of APP influenced the formation and further development of PP crystals remarkably. The crystallization and melting behaviors of the PP composites were affected by the rough surface of the microencapsulated APP, which was helpful for the formation of β-crystals and decreased the crystal growth rate compared with APP.

Understanding the performance and loss-mechanisms in donor–acceptor polymer based solar cells: Photocurrent generation, charge separation and carrier transport

Advances in bandgap and molecular spectral engineering have led to color-tunable donor–acceptor (DA) polymers for use in esthetically colored bulk-heterojunction (BHJ) photovoltaic devices where control and optimization of the physical processes governing their operation is necessary to realize high efficiency. We detail a study of the processes of photogeneration of charge carriers, their separation at the DA heterojunctions and their transport in solar cells fabricated from a series of dioxythiophene–benzothiadiazole (DOT–BTD) copolymers ( PG1– PG3) as the electron donor and methanofullerene ( PCBM) derivatives as the electron acceptor. We also examine the effect of the blend composition on carrier transport and photoresponse. The photogeneration of carriers and their dissociation increases with increase in concentration of the acceptor and peaks at ∼88% of PCBM. Measurements on single-carrier devices show that hole mobility in the polymer phase of the blends is enhanced by up to two orders at compositions having >80% of PCBM by weight. However, even at the optimized composition, the electron mobility in the blend is two orders of magnitude higher than the hole mobility. This largely imbalanced carrier transport results in the build-up of space-charges, limiting the efficiency of charge separation at short-circuit (∼53%) and the fill factor (<45%). To highlight the importance of attaining charge balance in BHJ DA blends for photovoltaics, we further investigate and compare solar cells from two model polymers, a low bandgap DA polymer ( PSBTBT) and poly-3-hexylthiophene ( P3HT), blended with PCBM. Our findings indicate that, in contrast to the DOT–BTD copolymers, carrier transport is significantly more balanced in these model systems, preventing space-charge build-up and reducing recombination, which results in a markedly improved charge separation efficiency and fill factor.

Development and application of cross-linked polyethylenimine for trace metal and metalloid removal from mining and industrial wastewaters

Pollution of water bodies by trace metals is an established problem and several studies have been conducted to deal with it. South Africa is amongst those countries whose water systems are most affected as a result of intensive mining activities. This research was dedicated to the development of an insoluble chelating polymer for use as an adsorbent for abstraction of metal ions from mining and industrial wastewaters. Polyethylenimine (PEI), well known for its metal chelating potential, was cross-linked by epichlorohydrin (ECH) in order to convert it into a water-insoluble form for direct use as an adsorbent. The binding affinity of the cross-linked polyethylenimine (CPEI) to heavy metal ions was assessed as well as its ability to be regenerated for re-use. CPEI exhibited good complexation ability to metal ions with high affinity to Cr and most divalent metal ions. The observed order of complexation was: Cr > Zn> Fe > Ni > Mn > Pb. On the other hand, it showed very poor ability to bind oxo-anions such as SeO3 2− and AsO2 − which has been attributed to the unavailability of suitable functional groups to interact with these ions.

Evaluation of a novel composite hydrogel polymer for use as a urinary tract biomaterial

Evaluation of a novel composite hydrogel polymer for use as a urinary tract biomaterial

Ultrafast resorbing polymers for use as carriers for cortical neural probes

We have identified a polymeric system based on a novel tyrosine-derived terpolymer that offers desirable insertion capability for flexible neural prosthetic devices. To test this concept, flexible films were coated with this terpolymer and their suitability for peranchyma insertion was visualized. The effect of the polymer on neural recording was evaluated using coated microwire probes. The stiff but readily resorbable polymer rapidly degrades (molecular weight half-life of 170 min) while turning into a soft gel, followed by complete resorption within 240 min. This polymeric platform maintains sufficient stiffness to facilitate pial penetration with a dry elastic modulus of 393 ± 44 MPa but loses its strength within 30 min once immersed in saline. In vitro, the polymer’s ability to locally deliver dexamethasone has been confirmed through a first order release profile over a 360 min period. In vitro, coated microwire probes regained their original impedance values of 0.5 KΩ within 20 min of wetting via water absorption and polymer resorption. In vivo, the retention of electrical recording capability was also demonstrated through multiple waveform detection in live animals. The ultrafast resorbing polymer as a platform to facilitate the implantation of micronized flexible probes can be utilized in future designs of chronic neural devices.

Carbazole/fluorene copolymers with dimesitylboron pendants for blue light-emitting diodes

A series of random and alternating carbazole/fluorene copolymers with various dimesitylboron-containing carbazole derivative contents were synthesized by Suzuki polymerization for use as a light-emitting layer in blue light-emitting diodes. Two carbazole derivatives, CzPhB and CzPhThB consisted of a carbazoyl group as the donor and a dimesitylboron group as the acceptor group, separated by phenyl and phenyl-thiophene groups π-conjugated systems, respectively. The copolymers exhibited good thermal stability and blue emission in both solution and the solid state. Moreover, the CzPhB/fluorene and CzPhThB/fluorene copolymers exhibited a higher PL quantum efficiency than the fluorene-based homopolymer (POF). Higher brightness and larger current efficiency were observed for the CzPhB/fluorene and CzPhThB/fluorene copolymer-based devices compared to the POF-based device. Additionally, the CzPhThB/fluorene copolymer-based devices had better EL performances than the CzPhB/fluorene copolymer-based devices. The turn-on voltage, maximal brightness, and highest luminescence efficiency of the carbazole/fluorene copolymer-based devices were found to be 4.5–8.5 V, 436 cd/m2, and 0.51 cd/A, respectively.

Silver nanoparticles as surface-enhanced Raman substrate for quantitative identification of label-free proteins

We developed a novel method to fabricate uniformly distributed silver nanoparticles (AgNPs) on nanostructured polymer for use as surface-enhanced Raman spectroscopy (SERS) substrates. Over 92% reproducibility on the same substrate was obtained in SERS analyses of benzenethiol (BT) using this novel substrate. The reproducibility of the BT SERS spectra collected from different substrates is >82%. The new SERS substrates were further used to quantitatively analyze label-free dipeptide in aqueous solution. The Raman signal is reproducible with levels above 91% for solution concentrations from 1 μg ml −1 to 1 ng ml −1 of the label-free dipeptide. The accurate and reproducible identification over a wide concentration range demonstrated that the new SERS substrate is suited for use in quantitative identification of biomolecules.

Direct nanoimprinting of metal oxides by in situ thermal co-polymerization of their methacrylates

The use of polymerization to solidify, strengthen and imprint liquid organic materials is the basis of ultraviolet (UV) nanoimprint lithography. In spite of these advantages, the use of polymerization to pattern materials in thermal nanoimprint lithography is almost non-existent. In this study, we demonstrate a facile and general method to directly imprint a host of unary metal oxides (Fe2O3, ZrO2, TiO2, Nb2O5 and Ta2O5) at a very high resolution viain situ thermal free radical co-polymerization of various metal methacrylates in the presence of cross-linker ethylene glycol dimethacrylate using a silicon mold. Polymerization during nanoimprinting rigidly shapes the patterns, traps the metal atoms, reduces the surface energy and strengthens the structures, thereby giving ∼100% yield after demolding. It was found that the higher oxidation state of metal resulted in excessive cracking of imprinted structures. This could be due to a higher degree of cross-linking of the precursor leading to shrinkage-related stress. Optimization of the resin composition by partially replacing ethylene glycol dimethacrylate with methyl methacrylate alleviated this problem. Heat-treatment of the imprinted structures resulted in the loss of organics, their subsequent shrinkage and converted the patterns to their corresponding metal oxides with line-widths as small as 25 nm.

Rapid prototyping of poly(dimethoxysiloxane) dot arrays by dip-pen nanolithography

We report the first direct patterning of elastomeric PDMS structures by dip-pen nanolithography (DPN). This method involves the use of a cantilever tip to transfer a PDMS ink onto a silicon dioxide surface to create dot array patterns which are then cross-linked and bonded irreversibly to the substrate. The chemical composition of the PDMS structures deposited by DPN was characterised by Raman microspectroscopy to provide an insight into the ink transfer process. This technique offers a significant advance in the ability to rapidly and easily produce programmable surface features from a widely used polymer for use in a variety of applications.