Elaboration of Poly(ε‐caprolactone)‐g‐TiNbO5 Nanocomposites via in situ Metal Complex Initiated Intercalative Polymerization

Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO₅ nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO₅ mineral pre‐treated by AlMe₃, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.

SEM image of the fractured surface of a PCL‐TiNbO₅ nanocomposite film.     

Design of a Microfluidic System to Investigate the Mechanical Properties of Layer‐by‐Layer Fabricated Capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.

Time series of video frames showing capsules being compressed into a constriction.     

Methionine‐Containing Poly(amino acid) Hybrid Fibers via Self‐Assembly at Aqueous Interface

Summary: Using sulfonium groups to create a novel fiber material, methionine‐containing hybrid fibers were prepared from S‐methylated poly(L ‐methionine) and poly(L ‐lysine, L ‐methionine) solutions with gellan solution by polyion complex (PIC) formation via self‐assembly at the aqueous interface. The breaking strain of the PIC fibers were increased by incorporation of methionine residues into the poly(L ‐lysine). These findings may provide a new approach for preparing a wool‐like fiber in aqueous media using the synthetic water‐soluble methionine‐containing poly(amino acid)s.

SEM image of Met‐containing PIC fiber: (a) poly[Met¹⁹Met(SMe)⁸¹]‐gellan fiber (magnification, ×500).     

Fracture Behaviour of Styrene/Butadiene Block Copolymers having Different Molecular Architecture

The crack toughness behaviour of styrene/butadiene block copolymers of triblock and star architectures was investigated using instrumented Charpy impact testing. In order to evaluate adequately the toughness behaviour of the investigated materials, different concepts of elastic‐plastic mechanics (J‐integral and crack‐tip opening displacement, CTOD concepts) were used. Although the lamellar block copolymers showed a remarkably enhanced ductility in the tensile test than the neat block copolymer having hexagonal PB cylinders in PS matrix, no pronounced difference in crack toughness was found. This behaviour implies that the tensile strain cannot be regarded as the only parameter defining the toughness value. A brittle/tough transition was observed in a lamellar star block copolymer on blending with a linear thermoplastic elastomeric SBS triblock copolymer.

SEM micrograph showing the details of the stable crack propagation region in a binary block copolymer blend.     

Synthesis and Characterization of Segmented Block Copolymers Based on Hydroxyl‐Terminated Liquid Natural Rubber and α,ω‐Diisocyanato Telechelics

Summary: Segmented block copolymers, consisting of non‐polar soft segments from hydroxyl‐terminated liquid natural rubber (HTNR) and polar hard segments from α,ω‐diisocyanato telechelics obtained by “criss‐cross”‐cycloaddition, have been synthesized. The block copolymer formation took place under relatively mild reaction conditions at 80 °C in dichloroethane in the presence of dibutyltin dilaurate as a catalyst. The resulting block copolymers were characterized by spectroscopic techniques (¹H NMR, FTIR, UV‐vis spectroscopy) as well as GPC for molar mass determination. The block copolymers were compression molded in a hot stage press, and the resulting samples were characterized by DSC and stress‐strain measurement. The solubility and phase morphology of the materials have also been studied.

Segmented block copolymer from HTNR and α,ω‐diisocyanato telechelics     

Synthesis and Characterization of Biodegradable Poly(ε‐caprolactone)‐Polyglycolide‐Poly(ethylene glycol) Monomethyl Ether Random Copolymer

Summary: Poly(ε‐caprolactone)‐polyglycolide‐poly(ethylene glycol) monomethyl ether random copolymers were synthesized from ε‐caprolactone (ε‐CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160 °C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, ¹H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG.

     

Layered Silicate‐Induced Enhancement of Fracture Toughness of Epoxy Molding Compounds over a Wide Temperature Range

Summary: The fracture toughness of EMC was dramatically increased over a wide temperature range by the addition of a very low volume fraction of layered silicates to EMC filled with micro‐silica particles. Layered silicate‐EMC nanocomposites containing intercalated and the exfoliated silicates were fabricated by using o‐cresol and biphenyl type epoxy resins, respectively. It was found that exfoliated silicates were more effective than intercalated silicates at toughening EMC at temperatures above T_g of the epoxy resin. Enhanced fracture toughness of EMC over a wide temperature range, from ambient to 230 °C has been attributed to the presence of layered silicates, which induces macroscopic crack deflection and severe plastic deformation in front of the crack tip.

     

Synthesis and Light‐Emitting Properties of New Polyimides Containing Ethynylene Units in the Main Chain

Two new polyimides (ODA‐PI and HDA‐PI) having 1,4‐phenylenediethynylene unit and octyloxy groups were synthesized. Judging from inherent viscosities of their precursor PAAs (1.42 and 1.62 dL · g^?1), the two PIs were very high in molecular weight. Casting and thermal imidization of PAAs results polyimides with good‐quality films. They were stable up to 364 °C and showed no crystallites. UV‐vis and PL spectra in NMP solutions of both PIs showed maxima at 442 and 501 nm, respectively, while PL spectra in ≈10 µm thick films exhibited a maximum at 540 nm. CV indicates that two PIs were electrochemically active in redox region. The devices with construction of ITO/PEDOT/PIs/BAlq₃/LiF/Al exhibited turn‐on voltages of 6.5 V in ODA‐PI and 7.5 V in HDA‐PI and emitted a bright bluish‐green light. ODA‐PI and HDA‐PI showed maximum luminescence of 256 and 316 cd · cm^?2, respectively, at the same voltage of 12 V.

     

Inhomogeneity Effects in Vapor Phase Polymerized PEDOT: A Tool to Influence Conductivity

Low‐MW urethanes were investigated to control domain formation as well as inhibiting cleavage reactions during vapor phase polymerization of PEDOT. A diurethanediol (DUDO) was identified as a highly efficient mediator for the process, resulting in PEDOT films exceeding conductivities of 1 000 S · cm^?1. All the urethanes investigated had the desired inhibiting effect on the polymerization, but all apart from DUDO also introduced unwanted domain formation on the micrometer scale. The addition of PEG generally improved conductivity by suppressing the domain formation and, with an optimized combination of DUDO and PEG, conductivities over 1 200 S · cm^?1 were achieved.

     

Iron(III) Chloride Catalyzed Synthesis of Highly Substituted Indolyl‐Tetrahydroquinoline Derivatives by Using Indolylnitroalkene as Dienophiles and Its Application to the Synthesis of Indolo‐Benzonaphthyridine Derivatives

An efficient iron(III) chloride catalyzed synthesis of highly substituted indolyltetrahydroquinoline derivatives from easily available starting materials, including indolylnitroalkenes, substituted anilines and various aldehydes is reported. The reaction utilized strong electron deficient dienophiles like indolylnitroalkene via a Povarov approach. The methodology shows good functional group tolerance and can be used to prepare fused indolo‐benzonaphthyridine derivatives.

     

Thermo‐Physical and Impact Properties of Epoxy Containing Epoxidized Linseed Oil, 2

Summary: Biobased neat epoxy materials containing epoxidized linseed oil (ELO) were processed with an amine curing agent. A defined amount of diglycidyl ether of bisphenol F (DGEBF) was replaced by ELO. The thermophysical properties of the amine‐cured biobased neat epoxy were measured by dynamic mechanical analysis (DMA). The Izod impact strength increased with an increase in the amount of ELO added. The change in the Izod impact strength was correlated with the thermophysical properties measured by DMA.

Relation between the Izod impact strength and loss factor for amine‐ and anhydride‐cured ELO‐containing epoxy resins.     

Aspects of the Softness and Hardness Concepts of Density-Functional Theory

In the density-functional theory of the ground state of an electronic system there arise the concepts of softness, hardness, local softness, and local hardness. Definitions of these quantities are reviewed, and then local softness and local hardness are discussed in some detail. The local softness of a species, the derivative , is a measure of the chemical reactivity of a site in the molecule. From it can be obtained the total global absolute softness in the sense of Pearson and a normalized chemical reactivity index of frontier type. Several formulas for s( r ) are obtained, including new fluctuation formulas, and its determinative role in chemisorption, catalysis, and frontier-controlled charge-transfer processes is briefly discussed. Local hardness is a corresponding appropriately defined functional derivative η(r) = [δμ/δp(r)]_v(r). Difficulties associated with ambiguities in this definition are discussed and resolved. It is concluded that for most purposes the best working formula for local hardness is , where η(r, r′) is the hardness kernel; , where F[p] is the usual Hohenberg-Kohn functional and f(r) is the Fukui function. With this definition, η(r) = η, a constant which is the global hardness. Just as the chemical potential equalizes in the ground state, so does the hardness. It is demonstrated that hardness can be taken to be an average of orbital contributions.     

The Solid State Postcondensation of PET, 2

Summary: A process for the solid state polycondensation of PET is proposed. It is shown that by correctly choosing the prepolymerisation conditions it is possible to crystallise the product and to directly polymerise it in a dispersed phase. This process is significantly faster than the “standard” PET processes, and allows one to obtain high molecular weights directly from a prepolymer without the need to use an intermediate solution polymerisation step.

Reactor set‐up for precursor preparation and dispersed phase prepolymerisation.     

Laccases to Improve the Whiteness in a Conventional Bleaching of Cotton

This study reports for the first time on the enhancement of the bleaching effect achieved on cotton using laccase enzyme. Laccases applied in short‐time batchwise or pad‐dry processes prior to conventional peroxide bleaching, improved the end fabric whiteness. The whiteness level reached in the combined enzymatic/peroxide process was comparable to the whiteness in two consecutive peroxide bleaches.

Effect of 10 min laccase pre‐treatment at 60 °C, pH 5 on fabrics whiteness before and after a conventional hydrogen peroxide bleaching.     

Ternary Gels of a Polymer Blend and a Recycled Oil: Their Use as Bitumen Modifiers

A blend of random ethylene‐vinyl acetate copolymer (EVA) and triblock styrene‐butadiene‐styrene copolymer (SBS) was dissolved in a recycled engine oil to obtain ternary thermoreversible gels. As the temperature was increased, first a network associated with EVA disappeared, and a second one associated with SBS dominated, maintaining the elastic response of the system. The principal advantage of these ternary systems is that their mechanical properties and thermal stability are better than that of binary gels. These gels, made from waste, can be used as bitumen modifiers to obtain binders of improved properties and good stability, which are useful for road surfacing.

Temperature sweeps of elastic modulus performed at a frequency of 1 Hz.     

Preparation and Structure of Porous Silk Sericin Materials

Summary: Porous materials of Bombyx mori silk sericin were prepared by freeze-drying. The effects of concentration of the sericin solution and that of freezing temperature on the structure and properties of materials were investigated. The results indicated that porous sericin materials, with average pore radius between 60 and 90 μm and porosity between 75 and 85%, could be prepared by freeze-drying. Thicker solution and lower freezing temperature resulted in smaller pore radius and porosity and moreover, bigger pore density. The condensed structure of interior sericin was mainly amorphous, and contained some crystal structure. Compared to the non-crosslinked porous sericin materials, the content of the β-sheet structure of the sericin materials, cross-linked by poly(ethylene glycol) diglycidyl ether, increased to some extent.

Cross section SEM photograph of the porous sericin material.     

Processing,Structure, and Properties of PAN/MWNT Composite Fibers

Conventional dry‐jet wet fiber spinning techniques were used to fabricate continuous PAN/MWNT composite fibers with up to 20 wt.‐% nanotube loading. PAN at the MWNT interface exhibited lower solubility under thermodynamically favorable conditions than in bulk PAN, indicating good interfacial interaction. Due to the PAN/MWNT interaction at the interface, thermal shrinkage decreases with increasing MWNT loading (5 to 20 wt.‐%). For high MWNT loadings, PAN/MWNT composite fiber at 15 wt.‐% MWNT loading showed an axial electrical conductivity of 1.24 S · m^?1. For all loadings, PAN/MWNT composite fibers exhibited higher tensile moduli than theoretically predicted by rule‐of‐mixture calculations, suggesting good reinforcement of the PAN by MWNT.

     

A Novel Route to Multiphase Polymer Systems Containing Nano‐Droplets: Radical Polymerization of Vinylic Monomers in Gelled Water‐in‐Oil Miniemulsions

Summary: A new strategy for the synthesis of composite polymers with larger volume fraction of aqueous inclusions less than 1 µm in diameter is presented. A water‐in‐oil miniemulsion of aqueous droplets in a continuous, cross‐linkable monomer phase is prepared. The addition of an organo‐gelator allows the immobilization of the droplets in a solid gel, thus avoiding the usual demixing upon polymerization of the continuous phase. This pregelled system is then converted into a composite polymer by photoinitiated free radical polymerization. Such coatings may be used for an improved climate control of buildings or as a deposit for the controlled release of actives from polar nano‐droplets.

SEM image of a cross‐linked composite polymer showing controlled droplet inclusions with a maximal diameter of 500 nm.     

Laser and Microwave Welding – The Applicability of New Process Principles

This article has been compiled on the basis of the many years' experience that has been acquired in the field of plastics welding by the Institute of Plastics Engineering (KTP) at the University of Paderborn. A brief report is given on the state of the art in laser and microwave welding technology. An overview is also included on the potential and limits of the use of laser and microwave welding in plastics processing. In the case of laser welding, a number of results achieved in welding of molded parts are presented that have been obtained in the course of extensive investigations. For microwave welding, a report is included on investigations that are currently running at the KTP. In addition to this, details are given on the basic suitability of laser and microwave welding for joining films and sheetings.

Configuration for the indirect microwave welding of panels, left: side view, right: cross‐section.