Lipase‐catalyzed polycondensation of two biobased diacids, 1,12‐dodecanedioic acid and 1,14‐tetradecanedioic acid, with 1,8‐octanediol was achieved using immobilized Lipase B from Candida antarctica. The procedure resulted in partially renewable prepolymers, while poly(octylene adipate) from petroleum‐based adipic acid was also synthesized for comparison reasons, revealing a dependence of the enzymatic polymerization degree on monomer composition. The prepolymers were further submitted to bulk postpolymerization at temperatures in the vicinity of their melting point under flowing nitrogen. The intrinsic viscosity increase was found up to 12%, with no significant impact on the polyesters thermal properties.
Toughness enhancement of S‐(S/B)‐S triblock copolymers via a molecular‐weight‐controlled pathway is demonstrated. The post‐yield crack toughness behavior of the triblock copolymers uniquely reveal a brittle‐to‐semiductile‐to‐ductile transition with increasing while keeping the basic molecular architecture fixed. TEM and SAXS investigations indicated three distinct morphologies as a function of χeffN as a consequence of the increase in : (i) a homogeneous structure without phase‐separation, (ii) a weakly segregated structure, and (iii) a lamellar structure. The increase in crack toughness is also reaffirmed from kinetic and strain field analysis studies concerning dynamics of crack growth in block copolymers with high PS content.
Two propylene copolymers with similar comonomer content and molecular weight were electrospun from solution. The 1‐octene and 1‐decene copolymers yielded ribbon‐like fibers. Isotactic poly(propylene) prepared by both heterogeneous and homogeneous catalyst systems could not be electrospun from the same solvent system used for the copolymers. The presence of the higher 1‐alkene comonomers in small amounts (about 1 mol‐%) not only affects the crystallinity of the polymer compared to the homopolymer, but appears to influence the solubility as well. The combined effect of lowering crystallinity and increasing solubility indicates that the use of higher 1‐alkene comonomers in low amounts could be a route to prepare poly(propylene) based electrospun fibers.
A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.
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.
This paper describes a novel process that is stretching‐controlled thermal micromolding, to fabricate bionic superhydrophobic polyethylene films. Low‐density polyethylene was thermally pressed in a vacuum oven onto PDMS stamps replicated from lotus leaves. After being cooled and peeled off from the stamps, the polyethylene films with superhydrophobic surface were created, exhibiting a water contact angle of 154.1 ± 3.5° and a rolling angle of ≈7°. SEM imaging showed that the superhydrophobic surface had micro‐papillas much higher than those on the lotus leaf, demonstrating the papillas had been stretched longer from the holes on the stamp during the separating process. This study shows that micromolding is a promising technique for large scale production of superhydrophobic films, even if the holes on the mold are not deep enough.
Temperature‐responsive PVCL homopolymers and functional PVCL polymers containing carboxylic acids are prepared in organic and aqueous solutions. PVCL bulk polymers are characterized using 1H NMR, photometry, ATR‐FTIR, and thermal analysis. A finite phase transition at 37–40 °C occurs in aqueous solutions of PVCL and PVCL‐COOH. PVCL and PVCL‐COOH polymers are electrospun into fibers ranging from 100 to 2300 nm in diameter. PVCL/cellulose bi‐component films are obtained by electrospinning of CA and PVCL followed by alkaline hydrolysis. These tunable thermo‐responsive PVCL/cellulose nanofibers have potential applications in developing affinity membranes.
Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.
End‐grained wood/polyurethane composites were obtained by a water‐based one‐pot process free of diisocyanates. Wood was impregnated with both PEG and CBC‐functionalized PEG as a coupling agent. A thorough study of the CBC‐mediated end‐groups conversion of PEG was achieved. It came out that functionalization conditions strongly affected the polyurethane chain extension and its grafting onto the wood structure. Antiswelling efficiency measurements showed that the one‐pot procedure allowed to reach comparable dimensional stabilization than the diisocyanate‐based process previously described. Morphological analysis demonstrated that such an improvement was attributable to the formation of cell wall‐bulked WPCs.
The solid and thermally instable azoinitiators V‐65 and VR‐110 were embedded within a polymer particle by using the miniemulsion process and afterwards quickly decomposed by thermal treatment below the glass temperature of the polymer. The resulting nitrogen gas overpressure inside the particles leads to a disruption of the polymer particle and a possible sudden release of encapsulated substances. It is shown, by electron microscopic measurements, that the number of burst particles correlates with the applied temperatures as well as the heating time. The surface deformation could be verified by scanning electron microscope analyses.
A siloxane‐grafted new diamino monomer DBPDMS has been prepared and used as a co‐monomer in combination with the fluorinated diamine monomer TFBB to prepare siloxane‐grafted polyimides. The polymers have been characterized by means of GPC, IR, and NMR. Their thermal, mechanical, and surface properties have been evaluated and compared with the homopolyimide and with polyimides where polysiloxane is incorporated in the main chain. DSC revealed melting of the grafted siloxane chain at sub‐ambient temperature and a glass transition corresponding to the main polymer chain at high temperature. Isothermal gravimetric analysis at 350 °C indicated that grafted siloxane moiety can be removed thermally from the polymer chain without affecting the polymer backbone.
The objective of this work was to investigate the influence of irradiation conditions on grafting of styrene into tetrafluoroethylene‐hexafluoropropylene‐vinylidene fluoride (THV) terpolymer films. Stress–strain measurements, infrared spectroscopy and electron paramagnetic resonance spectroscopy have been used to characterize the pre‐irradiated polymer films regarding tensile strength, elongation at break, changes in the chemical structure and concentration of trapped radicals, respectively. Main‐chain scissions associated with the formation of carbonyl end groups and end‐chain double bond structures have been identified to be the reason for a moderate deterioration of the mechanical properties of the pre‐irradiated films. The yield of grafting has been found to be influenced by THV grade, irradiation temperature and concentration of cross‐linker.
A new melt‐processable PTFE material is presented and characterized that provides new and economical solutions in polymer technology while bridging the gap between perfluorinated PTFE and fluorothermoplastic materials such as perfluoroalkoxy resins. Thermal transitions, MW and MWD, and microstructures of the melt‐processable PTFE materials are investigated and compared to standard PTFE, modified PTFE, and PFA materials. The influence of the polymerization type used for the preparation of the melt‐processable PTFE (emulsion and suspension polymerization) on the MWD and the comonomer distribution are discussed.
Poultry feather fiber is transformed into biothermoplastics using a twin screw extruder, and the plasticizing effect of four different plasticizers on the material properties is investigated. Conformational changes, viscoelastic behavior, thermal degradation, and phase transitions are assessed by means of FTIR spectroscopy, DMA, TGA, and DSC, respectively. The mechanical properties of the plasticized resins are assessed by tensile measurements, while optical transmittance is recorded using UV‐Vis spectrophotometry. The water uptake behavior of the fiber keratin and plasticized resins is also investigated.
Low density polyethylene (LDPE) was prepared into micro‐ or submicro‐spheres or nanofibers via melt blending or extrusion of cellulose acetate butyrate (CAB)/LDPE immiscible blends and subsequent removal of the CAB matrix. The sizes of the PE spheres or fibers can be successfully controlled by varying the composition ratio and modifying the interfacial properties of the blends. The surface structures of LDPE micro‐ or submicro‐spheres and nanofibers were analyzed using SEM and FTIR‐ATR spectroscopy. In addition, the crystalline structures of the LDPE nanofibers were characterized.
A simple process is described for preparing transparent composite sheets from soy‐oil‐based biopolyurethane (BioPU) with microcrystalline cellulose (MCC). The sheets are prepared by the reaction of a mixture of soy‐oil‐based polyol and petrochemical polyol with polymeric methyldiphenyl diisocyanate (pMDI) in the presence and absence of MCC reinforcement by compression molding. MCC is well dispersed in the PU matrix, and characteristic peaks for MCC and BioPU are shown by the FTIR spectra. Mechanical properties are substantially improved with increasing MCC content. DMA and TGA results show better thermal stability in comparison to the neat BioPU sheets.
A new flame retardant based on an ammonium phosphonate is studied with respect to its thermal decomposition and its mode of action in wood‐plastic composites (WPCs). The measurements are carried out by means of fire tests (cone calorimeter) and pyrolysis investigations (thermogravimetry, infrared spectroscopy). The flame retardant acts mainly in the condensed phase by increasing the amount of residue formed by the wood part in the WPC. Additional flame dilution is achieved by the release of water, ammonia and carbon dioxide during the decomposition of the flame retardant.
The first reported use of two‐dimensional mesh thermoplastic fibers in an epoxy matrix for mendable composites is presented, yielding 100% restoration of GIC, failure energy, and peak loads over repeated damage‐healing cycles. SEM imaging and EDS mapping showed different surface structures between CFRPp and CFRPf and confirmed strength recoveries were attained by delivery of EMAA to the fracture plane which enabled the fractured surfaces to rebind after heating to 150 °C for 30 min.
Blends of PET, PTT and PBT with the corresponding MCOs have lower melt viscosities than the pure polymers. This effect of MCOs on viscosity has the potential for exploitation in polymer fabrication and especially in the processing of composite materials. Thus, the blends can be more easily melt‐processed than the pure polymers, and the MCOs can then subsequently be converted in situ into high‐molar‐mass polymers by ED‐ROPs. No catalyst is needed for the ED‐ROPs. It was shown that suitable polymer/MCO blends can be obtained directly by carrying out cyclo‐depolymerizations at appropriate concentrations. Suitable polymer/MCO blends can also, almost certainly, be obtained by carrying out the original polyester syntheses at lower concentrations than normally used.
A novel multi‐compound electrospinning method is described, using high‐conductivity aqueous solutions for the inner fluid and low‐conductivity polymeric solutions for the outer fluids. The driving fluid among inner fluids at the equivalent conductivity is switched at a certain frequency. The switching of the Taylor cone results in the alternative embedding of inner components. Also, the number of inner capillaries is proportional to the encapsulation components. Therefore, our method might be useful to alternatively encapsulate a variety of water‐soluble materials in fibers.
