Showing papers in "Macromolecular Materials and Engineering in 2010"

Recent Advances in the Application of Natural Fiber Based Composites

Abstract: Natural fiber reinforced polymer composites are lightweight, economical and available in a variety of forms. They have low densities, comparable material properties, high molding flexibility and are environmentally friendly, making them a conceivable alternative to traditional fillers like mica, calcium carbonate and glass. By modifying either the resin system or the natural fiber, biocomposites can be designed for different applications ranging from products of commodity to aerospace, examples including electroactive papers, fuel cell membranes, controlled drug release mechanisms and biosensors. This review aims to analyze the advancement in the application of cellulose based materials in different sectors with a discussion of fundamental research in these areas.

Extrusion Processing and Properties of Protein-Based Thermoplastics

Abstract: Increasing interest in competitive, sustainable, and biodegradable alternatives to petroleum-based plastics has encouraged the developmentof protein-based plastics. The formation of a homogeneous protein melt during extrusion occurs through: denaturation, dissociation, unraveling, and alignment of polymer chains. The presence of covalent cross-links is unfavorable, decreasing chain mobility, increasing viscosity and preventing homogenization. Proteins have high softening temperatures, often above their decomposition temperatures. To avoid degradation, the required chain mobility is achieved by plasticizers. By understanding a protein's physiochemical nature, additives can be selected that lead to a bioplastic with good processability. The final structural and functional properties are highly dependent on the protein and processing conditions.

New Composite Elastomers with Giant Magnetic Response

Abstract: Novel magnetorheological elastomers (MRE) based on a highly elastic silicone rubber filled with carbonyl iron magnetic particles of 3―5 and 3―50 μm are synthesized. The effect of an external homogeneous magnetic field on the viscoelastic properties of these materials is studied by dynamic experiments (shear oscillations on a rheometer). It is shown that the magnetic response of the MRE increases with a decrease of the strain. At 1% deformation both the storage and loss moduli of the new MRE demonstrate a giant response to the magnetic field, namely, an increase of more than two orders of magnitude in both moduli in a field of 300 mT is observed. In addition, these new MREs show a twofold increase of the damping ratio, which is important for their application as tunable vibration absorbers.

Collagen Cryogel Cross‐Linked by Dialdehyde Starch

Abstract: A 3D spongy collagen cryogel was prepared using DAS as the cross-linker. FTIR and CD studies demonstrate that crosslinking is achieved through the reaction of the DAS aldehyde groups with the free amino groups in collagen without affecting the triple helix of collagen. SEM demonstrates that the cryogel has a heteroporous structure with interconnecting pores. DSC measurements reveal that the cryogels have improved thermal stability in comparison with pure collagen. Moreover, the ESR shows that the water uptake of the cryogel decreases with DAS content. Evaporation tests indicate that the cryogel can hold moisture for a long time. Since both collagen and DAS are nontoxic and the resultant cryogel is blood-compatible, the cryogel is expected to be useful, e.g., as wound dressing.

A New Biodegradable Flexible Composite Sheet from Poly(lactic acid)/Poly(ε-caprolactone) Blends and Micro-Talc

Abstract: The influence of talc loading on phase morphology of PLA/PCL/talc composites and improvement in resulting properties are reported. Talc-based composites of PLA/PCL blends were prepared by melt blending. SEM analysis demonstrates that PLA appears as discrete domain phase, while PCL acts as a bulk phase in the blend. Talc addition decreases PLA domain sizes and voids in the matrix. This results in significant improvement of oxygen and water vapor barrier properties of composite by 33 and 25%, respectively, at 3 wt.-% talc loading. DSC shows that talc acted as nucleating agent for PCL phase in the composite and improves its crystallinity. Various theoretical models based on dispersion and filler geometry are used to predict the tensile modulus and oxygen permeability.

Impact Modification of Polylactide with a Biodegradable Ethylene/Acrylate Copolymer

Abstract: The effectiveness and efficiency of an ethylene/acrylate copolymer in toughening semicrystalline and amorphous PLA through melt blending is studied. The mechanical properties, phase morphologies, miscibilities, and toughening mechanisms of the blends are assessed. The ethylene/acrylate impact modifier effectively improved the impact strength of the blends, regardless of the PLA type. The semicrystalline blends showed decreased tensile strength and modulus with increased impact modifier content. In contrast, the ductility, elongation at break, and energy to break increased significantly. The relatively low BDT temperature obtained for the PLA blends renders the ethylene/acrylate copolymer impact modifier a desirable additive to toughen PLA for use in cold temperatures.

Effect of the Deformation Temperature on the Shape‐Memory Behavior of Epoxy Networks

Abstract: The impact of the deformation conditions, specifically the temperature, on the shape-memory behavior and characteristics of epoxy SMPs is studied. By simply varying the temperature during deformation (i.e., the programming step of the SM effect), the ultimate strain of the formulated epoxy was improved three- to fivefold, thereby providing for an increased range of reachable deformation strains during SM thermo-mechanical cycling. This research unveils newly developed epoxy-based SMPs with improved deformability range and high strength with intrinsically good thermal and chemical stability.

Manipulated Electrospun PVA Nanofibers with Inexpensive Salts

Abstract: PVA nanofibers have been successfully prepared via an electrospinning process by optimizing the electrospinning operational parameters including applied voltage, polymer concentration, feed rate, and working distance. Inexpensive NaCI and Fe(NO 3 ) 3 are found to reduce the fiber size drastically (minimum of 157 and 169 nm, respectively) even at a low loading. The thermal stability is investigated by both thermogravimetric analysis and differential scanning calorimetry. Fourier transform infrared spectroscopy is utilized to characterize the functionality of the fibers and to investigate the interaction between PVA and inorganic additions. Glass transition and melting temperatures of the PVA fibers have slight change with the increase of the salt loading.

Scratch Resistance Enhancement of Polymer Coatings

Abstract: This review presents the state of the art regarding the improvement of scratch resistance of polymeric coatings. In particular, our attention is focused on the effect of inorganic nano-metric fillers on the scratch resistance of organic coatings. Two main strategies are described for the achievement of such nanostructured hybrid organic/inorganic coatings: either a top-down or a bottom-up approach.

Electrohydrodynamic Direct Writing of Biomedical Polymers and Composites

Abstract: A recently developed electrohydrodynamic printing method is described that can be used to create ordered structures and complex patterns using coarse processing needles and two polymeric materials. The results highlight the method's potential for direct 3D writing of biomedical polymers and composites for a variety of biomedical applications.

Highly Conducting Polypyrrole/Cellulose Nanocomposite Films with Enhanced Mechanical Properties

Abstract: PPy was synthesised by oxidative chemical polymerisation using xylan, CMC and NFC as additives. Conducting nanocomposite films were cast from aqueous slurries using doped PPy particles, CMC and NFC as the conducting and reinforcing phase, respectively. NFC-based composites had higher conductivity and lower mechanical properties than CMC-based homologues. SEM analysis showed that in PPy/NFC composites, PPy and NFC were arranged in two entangled networks, whereas, in PPy/NFC composites, CMC formed a continuous matrix around PPy particles, thus limiting conductivity. Mechanical properties of nanocomposite films were interpreted as reflecting the presence of different structures when using NFC or CMC as reinforcing phase.

Water Vapor Permeability of Poly(L-lactide)/Poly(D-lactide) Stereocomplexes

Abstract: PLLA/PDLA blend films with only stereocomplex crystallites as a crystalline species together with pure PLLA and PDLA films with only homo-crystallites as a crystalline species were prepared, and the effects of enantiomeric polymer blending, crystalline species, and crystallinity on the water vapor permeability were investigated. The WVT coefficient P of PLLA/PDLA blend films was 14―23% lower than that of pure PLLA and PDLA films in the crystallinity X c range of 0―30%. Amorphous PLLA/PDLA blend films have a much lower P than pure PLLA and PDLA films. The dependence of P on X c for blend films was stronger for X c = 0―30% than for X c =30― 100%. This dependence is discussed using the Nielsen model and the concept of "restricted" (or "restrained") and "free" amorphous regions.

Responsive Hybrid Polymeric/Metallic Nanoparticles for Catalytic Applications

Abstract: The aims of the current study were to synthesize new responsive polymeric microgels with embedded silver nanoparticles and then to employ these particles as catalyst for reduction reactions. To these ends, stimuli-responsive microgels from PNIPAAm and the chitosan derivative were firstly synthesized by free radical precipitation polymerization. Then, silver nanoparticles were synthesized inside these microgel networks by in situ reduction of AgNO3. These microgels were temperature/pH sensitive with a phase transition temperature of 32‐358C in water at pH ¼3 and 8, respectively. The catalytic activity of the Ag nanoparticles for the reduction of 4-nitrophenol can be tuned through the swelling or collapse of the responsive microgel network hosting the active nanoparticles.

ZnO-Based UV Nanocomposites for Wood Coatings in Outdoor Applications

Abstract: Nanocomposite UV coatings with adjustable properties for use on wood substrates in outdoor conditions were developed. Nanoscale ZnO was shown to be an efficient light absorber. Coatings were characterized in terms of elongation at brake, residual PI and double bond conversion, universal hardness, transparency, hydrophobicity, and yellowing. Coated samples were artificially weathered and studied with regard to their optical and mechanical properties, as well as to changes in brightness, transparency, hydrophobicity, and water permeability. The prepared wood coatings showed an increased weather fastness and improved optical properties. The suitability for use in outdoor conditions was assured by optimizing the elasticity of the coating and decreasing its water permeability.

Hydrolytic Depolymerization of PET in a Microwave Reactor

Abstract: Recycling of PET was examined using hydrolytic depolymerization in an alkaline solution under microwave irradiation. The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. The main products were the monomers TPA and EG. The effect of reaction temperature, time, amount of PET and alkaline concentration on the degree of PET depolymerization and TPA recovery was investigated. Microwave irradiation was found to reduce the time needed to achieve a specific degradation of PET significantly, with almost complete depolymerization occurring in 30 min at 180 °C and only 46 W of microwave power. Using a phase transfer catalyst (TOMAB) resulted in the same amount of unreacted PET but at significantly lower depolymerization temperatures.

Switchable Wettability of Thermo-Responsive Biocompatible Nanofibrous Films Created by Electrospinning

Abstract: Thermo-responsive PNIPAAm/PLLA nanofibrous films with tunable surface morphologies and better biocompatibility were prepared by electrospinning technique. The electrospun composite films possessed a "bead-on-string" structure. The wettability of nanofibrous films was observed by water CA measurements. The results showed that the electrospinning process and addition of PLLA did not change the thermo-sensitivity of PNIPAAm. The wettability of electrospun PNIPAAm/PLLA composite films could switch from superhydrophilic to superhydrophobic when the temperature increased from 20 to 50 °C. Electrospinning is a promising way to create stimuli-responsive surfaces with potential application in the design and tactics of controllable drug delivery system.

Rheology and Physical Characteristics of Synthetic Biodegradable Aliphatic Polymer Blends Dispersed with MWNTs

Abstract: PLA/PBAT blends and PLA/PBAT/MWNT nanocomposite systems were prepared via a melt mixing process to examine their thermal and rheological properties. To compare the polymer blend/MWNT nanocomposite with a pure polymer/MWNT nanocomposite, PLA/MWNT, PBAT/MWNT, and PLA/PBAT/MWNT nanocomposite systems were prepared. TEM and SEM were used to observe that one phase has better affinity with the MWNT, while the MWNT was found to increase both the thermal properties of the PLA/PBAT blends and rheological properties of the PLA/PBAT/MWNT nanocomposite with distinct shear-thinning behavior due to the addition of the MWNT. An increase in the storage (G') and loss (G') moduli for the PLA/PBT/MWNT nanocomposite was also observed.

A Magnetic Composite for Cleaning of Oil Spills on Water

Abstract: The production of magnetic polymer composites for cleaning of oil spills on water is investigated. The polymer matrix consists of a biopolymer material (alkyd resin), which is cured with TDI in the presence of a magnetic powder (maghemite, γ-Fe 2 O 3 ), which is incorporated into the final polymer material in situ. Obtained polymer resins were characterized through magnetic force, AFM and WAXS/SAXS, showing that the proposed preparation technique leads to production of magnetic nanocomposites. Additionally, oil removal tests performed with polymer beads showed that the polymer product can be used to remove considerable amounts of oil from the surface of aqueous environments. In the best case, one part of the polymer product could be used to remove more than eight parts of oil from water.

Electrospun Hybrid Soy Protein/PVA Fibers

Abstract: Rheological behavior and spinnability of biodegradable materials based on SPI and PVA were studied for the production of electrospun fibers. pH level, processing temperature, and heating time were adjusted to investigate the effects of denaturing of soy protein on the rheology of SPI/PVA solutions. The results show that zero shear viscosity and degree of shear thinning of the SPI solution can be controlled by adjusting pH level and thermal treatment. The continuous production of uniform SPI/PVA fibers was achieved by electrospinning. The presence and amount of soy protein in the electrospun fibers was determined by EMPA and elemental analysis, confirming that the SPI was well incorporated into the PVA and remained in the electrospun fibers.

Superamphiphobic Web of PTFEMA Fibers via Simple Electrospinning Without Functionalization

Abstract: This paper reports on a web of superamphiphobic fluoro-compound fibers that forms as a result of a typical electrospinning method without any additional treatment. An electrospun web of poly(2,2,2-trifluoroethyl methacrylate) fibers exhibits superamphiphobicity when the water and hexadecane contact angles both exceed 150°. The morphology of a web is modulated by changing the polymer solution concentration from 24 to 30 wt.-% with other fixed processing conditions. The fiber diameter length depends mainly on the polymer concentration. A web formed from a 26 wt.-% solution has the smallest and most uniform fiber diameter; it also has the highest robustness parameter on wetting, thus the highest water and hexadecane contact angles. This result offers the possibility of simple industrial production of an amphiphobic surface.

Effect of ABS Rubber Content on the Localization of MWCNTs in PC/ABS Blends and Electrical Resistivity of the Composites

Abstract: Three types of acrylonitrile-butadiene-styrene rubbers with different rubber contents were used in the preparation of PC/ABS/MWCNT composites It was found that localization of MWCNTs changes from PC to ABS phase when rubber content of ABS varies from 5 to 60% This is discussed by a combination of thermodynamics and kinetics Melting sequence and high viscosity of ABS are used to explain the localization of MWCNTs in the high viscosity ABS phase The relationship between the localization of MWCNTs and the electrical resistivity of the composite is also investigated

Nanoporous Films with Low Refractive Index for Large‐Surface Broad‐Band Anti‐Reflection Coatings

Abstract: Nowadays, nanoporous films are widely employed in biochemical applications or in opto-photonic devices such as displays, solar cells, or light-guiding systems. In particular, the technological feasibility of nanoporous layers with low refractive indices has recently enabled the development of high-efficiency anti-reflection coatings. In this paper, we report on hybrid polymer nanoporous films that can be fabricated in a single coating step with an industrial aqueous-based method on very large surfaces. Both high transparency and low refractive index are simultaneously achieved over the entire visible spectrum. We eventually demonstrate the potential of such films for broadband AR applications by combining them in a graded-index multilayer that reduces the surface reflectivity of a polymer substrate from 10% to few ‰.

Structural, Electrical, Mechanical, and Thermal Properties of Electrospun Poly(lactic acid)/Polyaniline Blend Fibers

Abstract: Conducting electrospun fiber mats based on PLA and PAni blends were obtained with average diameter values between 87 and 1 006nm with PAni quantities from 0 to 5.6 wt.-%. Structural characteristics of fiber mats were compared to cast films with the same amount of PAni and studied by SEM, SAXS, and AFM. Thermal properties offiber mats and castfilms were comparedby DSC analyses. Mechanical properties of fiber mats were also evaluated. It was found that electrospinning process governs the crystal structure of the fibers and strongly affects fiber properties. New properties of PLA/PAni blends are reported due to the size fiber reduction.

Effects of Freezing/Thawing Cycles and Cellulose Nanowhiskers on Structure and Properties of Biocompatible Starch/PVA Sponges

Abstract: Strong honeycomb like nanocomposite sponges were fabricated from starch and PVA by using repeated cycles of freezing and thawing and reinforcing with cellulose whiskers. Their structure and properties were investigated with WAXD, FT-IR, SEM, DMTA, rheological measurements, and LSCM. The results revealed that the repeated freezing/thawing cycles induced a physically crosslinked chain packing between starch and PVA, as well as a phase separation caused by the crystalline ice and syneresis. Thus, larger pores and tougher walls emerged in the sponges, leading to a high swelling degree. The sponges reinforced with cellulose whiskers exhibited improved dimensional stability and enhanced strength. These nanocomposite sponges are promising for wound dressing and tissue engineering applications.

Graphene Nanocomposites Prepared From Blends of Polymer Latex with Chemically Reduced Graphite Oxide Dispersions

Abstract: Graphene nanocomposites are prepared by chemical reduction of graphite oxide (GO) dispersion with vitamin C in the presence of SAN latex followed by melt compounding. In this process, GO is well dispersed in an aqueous SAN emulsion before reduction. During reduction the SAN latex is adsorbed on the graphene sheets of the chemically reduced GO (CRGO). After melt compounding of such hybrid particles with SAN, the nanocomposites show uniform dispersion of CRGO in SAN resulting in improved stiffness with respect to SAN/graphite. The reduction of GO in the presence of polymer latex represents a versatile route to graphene masterbatches and does not require either drying of GO or thermal GO expansion at high temperatures.

Controlling Fiber Repulsion in Multijet Electrospinning for Higher Throughput

Abstract: A novel electrospinning set-up has been developed to successfully electrospin multiple jets with controlled fiber repulsion using a plastic filter. This set-up shows reduced fiber repulsion as compared to a multineedle set-up, along with increased throughput. The effect of processing parameters on the fiber repulsion in a multineedle set-up was also studied. It was found that fiber repulsion could be reduced by controlling emitter voltage and emitter/collector distance. Other important parameters studied included fiber distribution and throughput. It was found that the plastic filter set-up produced fibers with lower mean diameters and better uniformity. This novel plastic filter design for electrospinning provides increased electrospinning rates with better fiber uniformity.

Fractionation and Analysis of an Impact Poly(propylene) Copolymer by TREF and SEC-FTIR

Abstract: TREF fractionation was combined with SEC-FTIR analysis to measure the compositional heterogeneity within a commercial impact PP copolymer. The chemical composition of all fractions was determined as function of their molecular weight distribution. This approach proved to be highly successful at identifying different constituents within fractions exhibiting bimodal molecular weight distributions. Furthermore, the determination of ethylene and propylene crystallinity distribution across the molecular weight distribution confirmed the morphological nature of each of the components of the bimodal distribution. It is demonstrated that the combination of TREF and SEC-FTIR provides a simple alternative to more time-consuming conventional ways of characterising impact PP copolymers of complex heterogeneity.

Morphology and Thermomechanical Properties of Melt‐Mixed Polyoxymethylene/Polyhedral Oligomeric Silsesquioxane Nanocomposites

Abstract: The influence of the functionalization of fully condensed POSS cages on the properties of POMbased nanocomposites is studied. POSS with different organic substituents [glycidylethyl, aminopropylisobutyl, and poly(ethylene glycol)] are taken into account and melt mixed with POM. Good dispersion was achieved upon the addition of amino functionalized POSS, leading to an increase on the thermal decomposition temperature under nitrogen atmosphere up to 50 8C. However, mm-size aggregates were observed for other nanocomposites. There is no significant change in other thermal properties of the nanocomposites. The relationships among these effects and the morphological characteristics of the systems were analyzed.