Showing papers in "Macromolecular Materials and Engineering in 2016"

Flame Retardancy of Polymers: The Role of Specific Reactions in the Condensed Phase

Abstract: Condensed-phase mechanisms play a major role in fire-retardant polymers. Generations of development have followed the concept of charring to improve fire properties. Whereas the principal reactions are believed to be known, the specific description for multicomponent systems is lacking, as is the picture across different systems. A two-step approach is proposed in general, and also presented in greater detail. The second step covers the specific reactions controlling charring, whereas the actual reactants are provided in the preceding step. This model consistently incorporates the variety of structure–property relationships reported. A comprehensive case study is presented on seven phosphorus flame retardants in two epoxy resins to breathe life into the two-step approach.

Recent progress on the design and applications of polysaccharide-based graft copolymer hydrogels as adsorbents for wastewater purification

Abstract: Copyright: 2016 Wiley. Due to copyright restrictions, the attached PDF file only contains the abstract of the full text item. For access to the full text item, kindly consult the publisher's website.

Enhancement of Mechanical and Self‐Healing Performance in Multiwall Carbon Nanotube/Rubber Composites via Diels–Alder Bonding

Abstract: Mechanically robust and self-healing rubbers are highly desired to satisfy the increasing demand of high-performance smart tires and related materials. Herein, a self-healing rubber nanocomposite with enhanced mechanical and self-healing performance based on Diels–Alder chemistry has been investigated. The furfuryl grafted styrene-butadiene rubber and furfuryl terminated MWCNT (MWCNT-FA) are reacted with bifunctional maleimide to form a covalently bonded and reversibly cross-linked rubber composite. Obvious reinforcing effect is obtained at high cross-linking density. Over 200–300% increase in the Young's modulus and toughness can be achieved in the rubber nanocomposites with 5 wt% MWCNT-FA. Meanwhile, the healing efficiency increased with MWCNT-FA content. MWCNT-FA plays dual roles of effective reinforcer and a kind of healant.

A Unique Double Percolated Polymer Composite for Highly Efficient Electromagnetic Interference Shielding

Abstract: This study has developed a carbon nanotube (CNT)/ethylene vinyl acetate (EVA)/ultrahigh molecular weight polyethylene (UHMWPE) composite with a unique double percolated conductive structure, in which only 20 wt% of CNT enriched EVA is needed to form a continuous conductive network. Compared with conventional double percolated conductive polymer composites (CPCs) which require filler-enriched polymer content up to 50 wt%, the low CNT/EVA content gives rise to an unprecedentedly increased effective CNT concentration in the CNT/EVA/UHMWPE composite. The double percolated composite exhibits electrical conductivity comparable to that obtained in CNT-loaded single EVA composite with five times of CNT content. Only 7.0 wt% CNT gives the composite an electromagnetic interference (EMI) shielding effectiveness of 57.4 dB, much higher than that of mostly reported CNT and graphene based CPCs. Absorption is demonstrated to be the primary shielding mechanism due to the numerous interfaces between UHMWPE domains and CNT/EVA layers facilitating multiple reflection, scattering, and absorption of the incident microwaves. The construction of unique double percolated structure in this work provides a promising strategy for developing cost-effective and high-performance CPCs for use as efficient EMI shielding materials.

PVA/Carbon Dot Nanocomposite Hydrogels for Simple Introduction of Ag Nanoparticles with Enhanced Antibacterial Activity

Abstract: The introduction of nanomaterials to hydrogels is an effective way to improve the mechanical properties of hydrogels. Herein, carbon nanodot (C-dot) as a new-found excellent nanomaterial is first added to polyvinyl alcohol (PVA) hydrogel to prepare PVA/C-dot hydrogel by freeze–thaw method. The appropriate size and plenty of surface functional groups make C-dot an ideal nucleating agent for PVA crystallization, which leads to form a denser and more uniform cross-linked network in PVA hydrogel, and in turn enhance the mechanical properties of PVA hydrogel. Compared to pure PVA hydrogel, about a 46.4% increase of tensile strength and 18.5% increase of elongation at break are achieved when the content of C-dot in PVA/C-dot hydrogel is 2 wt%, suggesting that C-dot can effectively improve the mechanical properties of PVA hydrogel. Besides, C-dot can endow PVA hydrogel with some new properties, such as fluorescence and reducibility. Herein, Ag nanoparticles are simply introduced and uniformly dispersed in PVA hydrogels with the help of reducibility of C-dot, which can greatly enhance the antibacterial activity of PVA/C-dot hydrogels, and enlarge their application potential in medical field.

Flexible and Bio-Based Nonisocyanate Polyurethane (NIPU) Foams

Abstract: The amine cure of cyclic carbonate blends, derived from renewable resources and carbon dioxide, in the presence of a liquid fluorohydrocarbon as physical blowing agent with no ozone depletion potential, enables the facile tailoring of flexible bio-based nonisocyanate polyurethane (NIPU) foams. Unlike conventional PU foams, neither isocyanates nor phosgene or aromatic amines are required as intermediates in NIPU foaming. Typically, rigid cyclic carbonates such as carbonated trimethylolpropane glycidylether (TMPGC) are blended together with the corresponding flexible cyclic carbonate such as ethoxylated TMPGC (EO-TMPGC) which lowers monomer viscosity and reactivity. This is reflected by higher pot life and gelation times for the cure with hexamethylene diamine (HMDA), improving NIPU foam processing. With increasing EO-TMPGC content, rigid TMPGC/HMDA-NIPU foams are rendered flexible and soft, as verified by simultaneously declining storage modulus and glass transition temperature. In this NIPU foam family, the TMPGC/EO-TMPGC (60 wt%/40 wt%) blend cured with HMDA in the presence of Solkane 365/227 affords flexible NIPU foams exhibiting low density, very good mechanical hysteresis, and tailored hardness, meeting the demands of various applications like automotive seating. Emission tests confirm the absence of critical compounds mentioned in the global automotive declarable substance list.

Mechanical and Thermal Properties of Thermoset–Graphene Nanocomposites

Abstract: Graphene has resulted in significant research effort to generate polymer nanocomposites with improved mechanical, thermal as electrical properties as compared to pure polymers. A large number of studies have been undertaken using different graphene derivatives, filler loadings, synthesis methods, and so on to obtain optimum filler dispersion as well as filler–matrix interactions, which are crucial for achieving significant enhancement in the properties, especially at low filler fraction. This review summarizes the mechanical and thermal properties of numerous studies carried out for the property enhancements of commercially relevant thermosetting materials such as epoxy, polyurethane, natural rubber, melamine formaldehyde, phenol formaldehyde, silicones, vinyl ester, cyanate ester, and unsaturated polyester resin.

Additive Manufacturing of Poly(propylene) by Means of Melt Extrusion

Abstract: Additive manufacturing (AM) processes can provide great input for solving recently encountered challenges of the global market such as mass customization, highly dynamic environments, and the decrease of time needed from a draft to final products. This study aims at contributing to the issue of material limitations typically present in AM by researching possibilities of directly using technically relevant and commercially available polymer granules in melt extrusion processes. In order to extend the knowledge on the processing of semicrystalline polymers in melt extrusion based processes, different temperature induced influences on mechanical and morphological properties are investigated for poly(propylene). Mechanical tests are conducted to evaluate the effects and interdependencies of substrate, extrusion, and cooling temperature. Finally, based on the identified mechanical and rheological behavior of the material, a process window for the used materials is suggested.

Fabrication of Thermally Stable Polysulfone Microcapsules Containing [EMIm][NTf2] Ionic Liquid for Enhancement of In Situ Self‐Lubrication Effect of Epoxy

Abstract: Microcapsules containing an ionic liquid (IL) are potential candidate materials for preparing in situ self-lubricating composites with excellent tribological properties. 1-ethyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl]imide ([EMIm]NTf2) IL encapsulated polysulphone microcapsules are synthesized. The mean diameter and wall thickness are about 128 μm and 10 μm, respectively. Microcapsules have excellent thermal stability, with a thermal degradation onset temperature of 440 °C compared to traditional lubricants-loaded microcapsules. In situ self-lubricating composites are prepared by incorporating the IL-encapsulated microcapsules into epoxy matrix. When the concentration of the IL microcapsules is 20 wt%, the frictional coefficient and specific wear rate of composites are reduced by 66.7% and 64.9% under low sliding velocity and middling applied load conditions, respectively, as compared to the neat epoxy. The tribological behavior of the self-lubricating composites is further assessed in different applied load and sliding velocity conditions. The in situ self-lubricating mechanism of composites is proposed.

Making Nonwoven Fibrous Poly(ε-caprolactone) Constructs for Antimicrobial and Tissue Engineering Applications by Pressurized Melt Gyration

Abstract: A pressurized melt gyration process has been used for the first time to generate poly(e-caprolactone) (PCL) fibers. Gyration speed, working pressure, and melt temperature are varied and these parameters influence the fiber diameter and the temperature enabled changing the surface morphology of the fibers. Two types of nonwoven PCL fiber constructs are prepared. First, Ag-doped PCL is studied for antibacterial activity using Gram-negative Escherichia coli and Pseudomonas aeruginosa microorganisms. The melt temperature used to make these constructs significantly influences antibacterial activity. Neat PCL nonwoven scaffolds are also prepared and their potential for application in muscular tissue engineering is studied with myoblast cells. Results show significant cell attachment, growth, and proliferation of cells on the scaffolds.

Two‐in‐One Composite Fibers With Side‐by‐Side Arrangement of Silk Fibroin and Poly(l‐lactide) by Electrospinning

Abstract: 1D fibers of Bombyx mori silk fibroin (SF) and poly(l-lactide) (SF-s-PLLA) with side-by-side parallel arrangement of the two components in a single fiber made by electrospinning are presented. The side-by-side arrangement in both randomly oriented and aligned two-in-one fibers was confirmed by scanning electron and confocal laser scanning microscope studies. The molecular orientation and secondary structure of SF and PLLA were dependent on the fiber alignment and annealing conditions. The two sides retained their individual secondary structure before and after annealing without affecting each other in a significant way. The two-in-one fibers after post treatment with methanol and heat at 80 °C showed tensile strength 16.5 ± 1.4 MPa, modulus 205 ± 20.6 MPa, and an elongation at break of 53 ± 8%.

Melt Processed PCL/PEG Scaffold with Discrete Pore Size Gradient for Selective Cellular Infiltration

Abstract: In order to develop scaffold able to mimic the natural gradient properties of tissues, biphasic and triphasic approaches were adopted. In this work, polycaprolactone/polyethylene glycol (PCL/PEG) scaffolds were prepared by using a combination of melt mixing and selective leaching without harmful solvents. The method permitted to develop three-layer scaffolds with high control of porosity and pore size. The mechanical properties were evaluated under physiological condition in order to simulate the real conditions of work. Co-culture of osteoblastic and fibroblastic mice cells were carried out in order to study the differential cellular permeation through the different pore size layers.

Annealing Induced Mechanical Reinforcement of Injection Molded iPP Parts

Abstract: The mechanical properties and microstructure of injection molded isotactic polypropylene parts with high orientation before and after annealing are analyzed. The mechanical properties of the annealed samples are improved effectively. Through thorough analysis of various structural characterizations, a microstructural model based on the fact that the total length of long period kept constant to analyze the variation of mechanical properties is proposed. It is suggested that the increase of overall crystallinity, the recombination of crystalline phase, and the increase of amorphous phase, respectively, are beneficial for the improvements of the strength, stiffness, and toughness of annealed samples.

Current Approaches in Improving Hemocompatibility of Polymeric Membranes for Biomedical Application

Abstract: Suitable membranes for blood-contacting medical applications need to be resistant in confrontation with blood proteins and cells, while possessing high blood compatibility and permeability at the same time. Herein, an overview of the recent advances and strategies that have been used to enhance the hemocompatibility of polymeric membranes is provided. The review focuses on two modification strategies: (i) physical modifications and (ii) chemical modifications. It also highlights the current progress in the design of hemocompatible-functionalized membranes for biomedical applications. Subsequently, the commonly applied biocompatibility tests are also discussed and finally the future perspectives of the application of polymeric membranes in the biomedical field are presented. (Figure presented.) .

Observation of Confinement-induced Self-Poling Effects in Ferroelectric Polymer Nanowires grown by Template Wetting

Abstract: The authors are grateful for financial support from the European Research Council through an ERC Starting Grant (Grant no. ERC-2014-STG-639526, NANOGEN). R.A.W. thanks the EPSRC Cambridge NanoDTC, EP/G037221/1, for studentship funding.

Self-Cleaning, Thermoresponsive P(NIPAAm-co-AMPS) Double Network Membranes for Implanted Glucose Biosensors

Abstract: A self-cleaning membrane that periodically rids itself of attached cells to maintain glucose diffusion could extend the lifetime of implanted glucose biosensors. Herein, we evaluate the functionality of thermoresponsive double network (DN) hydrogel membranes based on poly(N-isopropylacrylamide) (PNIPAAm) and an electrostatic co-monomer, 2-acrylamido-2-methylpropane sulfonic acid (AMPS). DN hydrogels are comprised of a tightly crosslinked, ionized first network [P(NIPAAm-co-AMPS)] containing variable levels of AMPS (100:0-25:75 wt% ratio of NIPAAm:AMPS) and a loosely crosslinked, interpenetrating second network [PNIPAAm]. To meet the specific requirements of a subcutaneously implanted glucose biosensor, the volume phase transition temperature is tuned and essential properties, such as glucose diffusion kinetics, thermosensitivity, and cytocompatibility are evaluated. In addition, the self-cleaning functionality is demonstrated through thermally driven cell detachment from the membranes in vitro.

A Precursor Approach to Electrospun Polyaniline Nanofibers for Gas Sensors

Abstract: Polyaniline (PANI) has served as one of the most promising conducting materials in a variety of fields including sensors, actuators, and electrodes. Fabrication of 1D PANI fibers using electrospinning methods has gained a significant amount of attention. Due to the extremely poor solubility of PANI in common organic solvents, fabrication of electrospun PANI fiber has been carried out either by using corrosive solvents such as H2SO4 or by electrospinning in the presence of other matrix polymers. Herein, a new approach to the fabrication of PANI fibers using tert-butyloxycarbonyl-protected PANI (t-Boc PANI) as the conducting polymer precursor is reported. The t-Boc PANI is soluble in common organic solvents (e.g., chloroform and tetrahydrofuran), and electrospinning of t-Boc PANI in those solvents affords nano/micrometer-sized t-Boc PANI fibers. Treatment of the electrospun t-Boc PANI fibers with HCl results in the removal of the acid labile t-Boc group and the generation of conducting (≈20 S cm−1) PANI fibers. The HCl-doped PANI fibers are successfully used in the detection of gaseous ammonia with a detection limit of 10 ppm.

Polypyrrole‐Coated PDMS Fibrous Membrane: Flexible Strain Sensor with Distinctive Resistance Responses at Different Strain Ranges

Abstract: Flexible sensors capable of detecting large strain are very useful for health monitoring and sport applications. Here a strain sensor is prepared by applying a thin layer of conducting polymer, polypyrrole (PPy), onto the fiber surface of an elastic fibrous membrane, electrospun polydimethylsiloxane (PDMS). The sensor shows a normal monotonic resistance response to strain in the range of 0–50%, but the response becomes “on-off switching” mode when the strain is between 100 and 200%. Both response modes are reversible and can work repeatedly for many cycles. This unique sensing behavior is attributed to overstretching of the polypyrrole coating, unique fibrous structure, and elasticity of PDMS fibers. It may be useful for monitoring the states where motions are only allowed in a particular range such as joint rehabilitation.

Programmable Oil/Water Separation Meshes: Water or Oil Selectivity Using Contact Angle Hysteresis

Abstract: We report a novel method for oil/water separation using stainless steel meshes functionalized with amphiphilic copolymer, poly(methacrylic acid-co-ethylhexylmethacrylate) (PMAA-co-EHMA), brushes. Because the PMAA-co-EHMA brush-covered surfaces show a large contact angle hysteresis at the oil/water contact line, the meshes can be programmed to act as either water-selective or oil-selective filters simply by pre-wetting the mesh with one of these liquids. These programmable meshes can separate oil/water mixtures to high filtrate purities (more than 99 % mol/mol) in both oil-selective and water-selective modes.

High Strength Self‐Healing Magnetic Elastomers With Shape Memory Effect

Abstract: Development of self-healing and shape memory elastomers is important for artificial smart materials. Here, a novel shape memory magnetic elastomer with high mechanical strength consisting of conventional polymer and Fe3O4 nanoparticles is reported. The elastomer exhibit superparamagnetism, and superior self-healing performance at elevated temperature. The tensile strength of the healed elastomer can be up to 12.0 MPa, and almost equal to that of virginal sample. These materials are capable of remote controlling in shape memory process and actuating behavior, and can be used in many applications, ranging from wireless-controller to actuator or biomedical devices, and other remote shape memory systems.