The flame retardancy and mechanical properties of polyamide‐6 (PA6)/aluminum diethylphosphinate (AlPi) composite are greatly improved by the addition of novelly synthesized phosphorus flame retardant‐based diepoxide (DEP) during extrusion. The PA6/AlPi/DEP composite passes V‐0 rating of UL94 test with limiting oxygen index (LOI) of 32.6% at 13 wt% AlPi and 1 wt% DEP, as revealed by the results of flammability. The synergistic flame retardation mechanism offered by the two additives (AlPi and DEP) is studied in terms of in‐depth characterization of the charred residue and evolved gas. The deteriorated mechanical strength of PA6 due to existence of AlPi is compensated by the simultaneous chain extension effect of DEP. Accordingly, the flexural and impact strengths of PA6/AlPi/DEP composite are even superior to those of neat PA6.
Four bromine‐containing methacrylates 1 – 4 are synthesized from pentaerythritol tribromide and 2,2,2‐tribromoethanol and are characterized by 1H and 13C NMR spectroscopy. Their free radical polymerization is performed in dimethylformamide (DMF), using 2,2′‐azobis(2‐methylpropionitrile) as initiator. The photopolymerization behavior of monomers 1–4 is investigated using a differential scanning calorimeter. Homopolymerizations and copolymerizations with 2‐hydroxyethyl methacrylate are carried out. Both the presence of a carbamate group and of bromine atoms result in an increase of the polymerization rate. Dental resins are prepared by replacing a certain amount of 2‐(4‐cumyl‐phenoxy)ethyl methacrylate by monomers 3 and 4 in a model formulation. The incorporation of these methacrylates leads to a significant increase of the radiopacity. Resins based on monomer 4 exhibit improved mechanical properties.
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.
Colloidal assemblies of inorganic nanoparticles dispersed in liquid media hold particular promise for the creation of a unique class of functional materials with innovative applications. In the present report, “compound‐eye”‐like core–shell and Janus‐type silica and amino‐terminated 1,2‐polybutadiene (PB‐NH2) and polystyrene (PS) composite microspheres are successfully prepared by simply mixing an aqueous dispersion of silica particles into a tetrahydrofran (THF) solution of PB‐NH2, and PB‐NH2 and PS blends, followed by evaporation of the THF. This co‐precipitation process provides a new approach for producing organic–inorganic composite particles without the need for surface modification of the inorganic nanoparticles.
Nanogels loaded with fluorescent dextran as a model drug are synthesized by the oxidation induced cross‐linking of water soluble redox responsive thiolated poly(amino acid) in miniemulsion without the introduction of any cross‐linker molecule. Two types of high energy methods, namely, ultrasonication and high pressure homogenization (HPH), are compared. Dynamic light scattering and transmission electron microscopy measurements confirm that spherical nanogels in 100–150 nm diameter range are prepared successfully by HPH method. Size and surface charge of the nanogels can easily be controlled by environmental pH. The release of encapsulated drug is triggered by the degradation of nanogels in reducing environment due to the cleavage of disulphide bonds.
The fabrication of asymmetric polymer membranes via vapor phase deposition is demonstrated. In this solventless process, the dense layer is deposited first and then the porous layer is subsequently deposited onto the dense layer. A variety of functional polymer membranes can be produced by varying the precursor molecules. The functionality of the dense and porous layers can be independently tailored to be either hydrophobic or hydrophilic, resulting in membranes that are fully hydrophilic, fully hydrophobic, or asymmetric in both structure and chemical functionality. The thickness of both the porous and dense layers can be separately tuned by controlling the deposition time.
Mechanical properties and fracture mechanisms of Novatein thermoplastic protein and blends with core–shell particles (CSPs) have been examined. Novatein is brittle with low impact strength and energy‐to‐break. Epoxy‐modified CSPs increase notched and unnotched impact strength, tensile strain‐at‐break, and energy‐to‐break, while tensile strength and modulus decrease as CSP content increases. Tg increases slightly with increasing CSP content attributed to physical crosslinking. Changes to mechanical properties are related to the critical matrix ligament thickness and rate of loading. Novatein control samples display brittle fracture characterized by large‐scale crazing. At high CSP content a large plastic zone and a slow crack propagation zone in unnotched and tensile samples are observed suggesting increased energy absorption. Notched impact samples reach critical craze stresses easily regardless of CSP content reducing impact strength. It is concluded that the impact strength of thermoplastic protein can be modified in a similar manner to traditional thermoplastics.
A versatile approach to synthesis of hydrophobic polymeric cryogels is proposed using acetic acid crystals instead of ice crystals as porogen through cryo‐polymerization. In the range of 60 to 90 vol% of acetic acid, polymerization at ambient temperature gives rise to particulate polymers in beaded or amorphous shape, while polymerization at 4 °C, lower than the melting point of acetic acid (16.6 °C), leads to the formation of cryogel‐like monoliths with supermacroporous structure, which is mainly ascribed to cryo‐concentration effect. According to the measurements by scanning electron microscopy and mercury intrusion porosimetry, the dried samples are supermacroporous with pore size mainly ranging from several micrometers to several hundred micrometers, which can be feasible for rapid mass transfer. The forming cryogels display a superfast responsiveness to organic solvents, possibly stemming from their supermacroporosity and distinctive hydrophobicity.
Nanofiber‐based hydrocolloid scaffold is prepared by colloid electrospinning of thermoplastic polyurethane (TPU)/sodium carboxymethyl cellulose (S.CMC) in tetrahydrofuran (THF)/dimethylformamide (DMF). The most suitable process of electrospinning for successful formation of fibers is investigated by controlling the concentration of polymeric solution and co‐solvent ratio. In order to accomplish high wettability, the amount of colloid (S.CMC) and the co‐solvent ratio (THF/DMF), which affects the morphology of fibers, are adjusted. Finally, the open wound healing effect is confirmed using nanofiber‐hydrocolloid from in vivo animal studies. A detailed study of the wound healing process is also demonstrated for the first time.
A conjugated polymer, poly(9,9‐bis(6‐bromohexyl)‐9H‐fluorene‐alt‐1,4‐phenylene), is synthesized, converted to nanoparticles via a nanoprecipitation process, and utilized to fabricate thin films including conjugated polymer nanoparticles. The nanoparticles with surface bromides can be conjugated with an amine‐functionalized dendrimer via a nucleophilic coupling reaction. Thus, when microliter solutions of the particulates are dragged at a constant velocity on substrates alternately in a layer‐by‐layer manner, thin films composed of the nanoparticles and dendrimers can be successfully built up on the substrates. Our results suggest a methodology to control the deposition of thin films bearing conjugated polymer nanoparticles while minimizing processing time and decreasing material consumption.
Three different dopants are used to fabricate electrospun dopants/polystyrene (dopants/PS) composite fibers from PS solution and PS sol. The relative humidity and the influence of the dopants on the morphologies, diameter, porous structures, and dopant distribution of electrospun PS fibers are investigated. Compared to those obtained from PS solution, electrospun dopants/PS composite fibers from PS sol with hollow‐porous and multichannel hollow‐porous structures present significant advantages due to the multi‐stage degree of interfacial structure and diversity of the internal environment. In comparison to coaxial electrospun PS fibers, the electrospun dopants/PS composite fibers from PS sol obtained in one step have an improved yield and a simplified technological process simultaneously, leading to significant competitiveness in fields such as catalysis, fluidics gas storage, and sensing.
A new stereo pentablock copolymer consisting of poly(l ‐lactide) (PLLA: A), poly‐d ‐lactide (PDLA: B), and poly(butylene succinate) (PBS: C) is synthesized by two‐step ring‐opening polymerization of d ‐ and l ‐lactides in the presence of bis‐hydroxyl‐terminated PBS prepolymer that has been prepared by the ordinary polycondensation. The pentablock copolymers (PLLA‐PDLA‐PBS‐PDLA‐PLLA) as well as the triblock copolymers (PLLA‐PBS‐PLLA) obtained as the intermediates show different properties depending on the polymer compositions. In the pentablock copolymers, the direct connection of the PLLA and PDLA blocks allows easy formation of the stereocomplex crystals, while the introduction of the semicrystalline PBS block is effective not only for changing the crystallization kinetics but also for imparting an elastomeric property.
Most insect eyes use microvillar photoreceptors, where the visual pigment rhodopsin is aligned within tubular microvilli, endowing the insects with amazing navigation ability through detecting the polarization of illuminating light in the sky. Herein, polydiacetylene‐polystyrene (PDA‐PS) hybrid microfibers are fabricated by electrospinning method and it is demonstrated that PDA‐PS hybrid microfibers exhibit interesting polarized waveguiding properties, which is found to be dependent on the ordered alignment of PDA chains, but not on the propagating distance or the wavelength of the excitation light. Moreover, three PDA‐PS microfibers with different polarized waveguiding behavior can be assembled together as polarization sensitive photoreceptors to mimic the natural rhabdome arrays in insect eyes, since the physical dimensions, structure, and function of single PDA‐PS microfiber are comparable to that of natural rhabdomere.
Porous polymer materials prepared from biodegradable polymers have received considerable attention due to their potential as cell culture scaffolds for tissue engineering. Porous materials are generally sterilized by autoclaving prior to use as cell culture scaffolds to avoid unexpected biological infection. However, the melting point of biodegradable polymers is typically lower than the temperature used in autoclave sterilization. Here, the preparation of honeycomb films comprising a poly(L‐lactic acid) (PLLA) and poly(D‐lactic acid) (PDLA) stereo complex is described and their thermal stabilities are evaluated. The hierarchic photochemical patterning of PLLA/PDLA stereo complex honeycomb‐patterned films by UV‐O3 treatment is also demonstrated.
This paper reconstructs the principle of rubber incorporation in high impact poly(propylene) (hiPP) particles. The detailed information about the pores and rubber distribution inside and on the surface of hiPP particles is obtained by micro‐computed tomography and atomic force microscopy. The strong effect of homopolymer origin on hiPP particle morphology and rubber distribution is demonstrated. To obtain the most homogeneous rubber distribution, the low homopolymer porosity is required. The initial particle porosity has a negligible effect on the thickness of the rubber layer on the particle surface at the medium rubber content. The rubber forms not only along the iPP primary particles and directly or close to the pores but also on or close to the particle surface rather than it flows there. The evidence for these claims is based on the systematic investigation in dependence on EPR content, homopolymer particle porosity (prepared by different catalysts) and antistatic agent deactivating catalyst close to particle surface.
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.
This article deals with the amine blush phenomenon in epoxy coatings. Amine blush is due to amine carbonation and weakens the visual aspect of room temperature epoxy coatings. This paper describes a way to avoid the carbonation by preparing aminotelechelic prepolymers is described. For the first time, the amine‐adduct impact over amine carbonation, as well as the amine decarbonation with temperature, has been investigated by infrared spectroscopy. Moreover, a range of epoxy materials displaying various Tg are synthesized from amine‐adducts and compared to polyurethane references generally used for transparent coating applications. Mechanical and thermal properties are also investigated.
The combination of experimental and numerical approaches is attempted to shed more light on 3D microstructural imperfections and mechanical performance of 3D printed acrylonitrile butadiene styrene parts. The starting point is the virtual building of airy structures using a reverse engineering approach. This approach combines microstructure generator, finite element model, and optimization strategy to propose virtual airy structures satisfying structural and mechanical criteria up to a desired porosity content of 60%. Optimal structures are printed using fused deposition modeling and X‐ray microtomography is used to assess all microstructural defects. Compression testing is performed for load levels above 50% of reduction in sample height. The main outcome of this work is the demonstration of small amount of process induced porosity inducing high pore connectivity. The interdependence of process induced and desired porosity reveals genuine microstructural effects that are only characteristics of 3D printed materials.
Micellar radical polymerization of a short‐chain polyester macromonomer, polycaprolactone choline iodide ester methacrylate (PCLnChMA), is used to produce a new cationic flocculant that becomes more hydrophobic in response to hydrolytic degradation. The cationic tips of the comb‐like poly(PCL3ChMA) accelerate the settling rate of oil sands tailings, while partial hydrolysis of the polyester grafts reveals the hydrophobic segments that reduce capillary suction time by 30%. This technology combines the material properties of polyesters with the productivity of radical polymerization to make dual functional flocculants with characteristics that can be easily tuned to control flocculation performance, such as polymeric cation density, hydrophobic content, and polymer architecture.
Interfacial polymerization of dopamine and terephtaloyl chloride is performed on a porous crosslinked polyacrylonitrile support membrane. The resulting polymer layer has a smooth surface and is ultrathin (about 5 nm). The chemical nature of the interfacially polymerized layer is characterized by Fourier transform infrared spectroscopy and by X‐ray photoelectron spectroscopy. The thin‐film composite membrane is stable in aggressive solvents like dimethylformamide (DMF) and the membrane shows high solvent permeances combined with a molecular weight cut‐off below 800 g mol‐1. The remarkable stability in DMF, the ease of preparation as well as the extremely thin and smooth selective layer make this new type of bioinspired membrane attractive for solvent resistant nanofiltration.
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