A High‐Throughput,Controllable, and Environmentally Benign Fabrication Process of Thermoplastic Nanofibers

Continuous and uniform yarns of thermoplastic nanofibers were prepared via direct melt extrusion of immiscible blends of thermoplastic polymers with CAB and subsequent extraction removal of CAB. Ratios of thermoplastic/sacrificial polymers, melt viscosity, and interfacial tensions affect the formation of nanofibers. Dominating sacrificing polymer content in the blends and low interfacial tensions between thermoplastic polymer and CAB are two key factors. This fabrication process possesses features of high productivity, versatility of thermoplastics, controllability, and environment friendliness in manufacturing thermoplastic nanofibers.

     

The Solid State Postcondensation of PET, 4

Summary: A new method of polymerising PET in the solid state is proposed in either a gas phase reactor, or in hydrocarbon dispersion. It is shown that the reaction can be carried out efficiently at temperatures on the order of 200–240 °C directly from a prepolymer without the need for a melt phase step. It is shown that the crystal structure of the prepolymer plays a determining role in the kinetics of the SSP reaction.

Schema of the reactor used for gas phase SSP.     

The Effect of Disinfection Methods on the Mechanical Properties of Thermoplastic Recyclates

Summary: Increasing environmental concern encourages the development of new ways to recycle medical products. Post‐consumer medical products are suited for recycling because of their life‐span, but used products have to be disinfected before recycling. Therefore, the influence of different disinfection processes during recycling on the processibility and the mechanical properties of thermoplastics was investigated. As disinfection processes, steam disinfection and disinfection with electron beam and gamma radiation were selected. The characterisation of the properties of disinfected recyclates was undertaken for PE and PP from syringes. The melt mass‐flow rate (MFR), the dynamic mechanical properties, the tensile properties and fracture mechanics parameters were examined. A comparison of the results showed that stiffness and strength remain nearly constant, but the deformation and fracture behaviour tends to be influenced. The selection of appropriate disinfection parameters can avoid unnecessary alteration of the properties. Thus, steam disinfection as well as radiation disinfection up to a dose of about 25 kGy are suited for decontaminating used medical products.

Scheme of the influence of different disinfection methods on selected properties of thermoplastic recyclates.     

Production of Thermoplastic Starch/MMT‐Sorbitol Nanocomposites by Dual‐Melt Extrusion Processing

A “green” processing method, dual‐melt extrusion, was used to prepare thermoplastic starch/montmorillonite nanocomposites without organic reactions in the solution. XRD demonstrates that sorbitol enlarged the interlayer distance of MMT during the first step. MMT‐sorbitol, formamide and starch were used to obtain TPS/MMT nanocomposites in the second step. XRD and TEM reveal that TPS intercalated the layers of MMT. With increasing MMT content, improvements in thermal stability, tensile strength, Young's modulus and energy break, and a slight decrease of elongation at break, appeared. The effect of water content on the tensile strength and elongation at break was also studied.

     

Comparison of the Effects of an Ionic Liquid and Other Salts on the Properties of Electrospun Fibers, 2 – Poly(vinyl alcohol)

Understanding the effect of conductivity in electrospinning solutions is crucial in order to improve or control the electrospinning process. In this paper the effect of adding small amounts (0.039–0.259 mol · kg^?1) of three different conductive additives to aqueous solutions of polyvinyl alcohol has been investigated. The salts were HMICl (a room temperature ionic liquid), TEBAC (a quaternary ammonium salt) and KCl. Addition of these salts caused a steady increase in the solution conductivity but the fiber diameter was typically greater than that of PVA alone, and exhibited an oscillatory trend. The oscillatory trend on the fiber diameter is attributed to fiber backbuilding and fusion that occurs prior to deposition on the collector.

     

Reactive Compatibilizer Precursors for LDPE/PA6 Blends, 4

Summary: The effectiveness of some thermoplastic elastomers grafted with maleic anhydride (MA) or with glycidyl methacrylate (GMA) as compatibilizer precursors (CPs) for blends of low density polyethylene (LDPE) with polyamide‐6 (PA) has been studied. The CPs were produced by grafting different amounts of MA or GMA onto a styrene‐block‐(ethylene‐co‐1‐butene)‐block‐styrene copolymer (SEBS) (KRATON G 1652), either in the melt or in solution. A commercially available SEBS‐g‐MA copolymer with 1.7 wt.‐% MA (KRATON FG 1901X) was also used. The effect of the MA concentration and of other characteristics of the SEBS‐g‐MA CPs was also studied. The specific interactions between the CPs and the blends components were investigated through characterizations of the binary LDPE/CP and PA/CP blends, in the whole composition range. It was demonstrated that the SEBS‐g‐GMA copolymers display poor compatibilizing effectiveness due to cross‐linking resulting from reactions of the epoxy rings of these CPs with both the amine and the carboxyl end groups of PA. On the contrary, the compatibilizing efficiency of the MA‐grafted elastomers, as revealed by the thermal properties and the morphology of the compatibilized blends, was shown to be excellent. The results of this study confirm that the anhydride functional groups possess considerably higher efficiency, for the reactive compatibilization of LDPE/PA blends, than those of the ethylene‐acrylic acid and ethylene‐glycidyl methacrylate copolymers investigated in previous works.

SEM micrograph of the 75/25 LD08/PA blend (with 2 phr SEBSMA1).     

Melt Mixing of a Styrene/Butadiene Copolymer with an Aqueous Slurry of Zirconium Phosphate as a Route for the Preparation of Nanocomposites

The preparation of functional nanocomposites by dispersion of a synthetic lamellar α‐ZrP within a styrene/butadiene random copolymer during melt compounding is described. It is shown how the physical and chemical incompatibility of filler and polymer can be overcome, and problems arising from the low viscosity ratio between slurry and polymer matrix are discussed. The aqueous phase can easily be eliminated at the end of the process. The dispersion of the ZrP requires the use of intercalants, and alkylamines were used for this purpose. XRD and TEM are used to characterize the degree of organization of ZrP in the slurries and in the matrix. DMA helps to understand the origin of the limited reinforcing effect.

     

Thermal‐ and Sun‐Promoted Generation of Silver Nanoparticles Embedded into Poly(vinyl alcohol) Films

Nanocomposites based on poly(vinyl alcohol) and silver nanoparticles were efficiently prepared by sun‐ and thermal‐promoted reduction processes. Uniaxial drawing of the Ag/PVA nanocomposites favoured the anisotropic distribution of silver particles, providing oriented films with polarisation‐dependent tunable optical properties. These dichroic properties were more pronounced for nanocomposites produced by sun exposition, which provided more compact and interacting metal clusters. The results obtained suggest the nanocomposite films could find potential applications as colour polarising filters, radiation responsive polymeric objects and smart flexible films in packaging applications.

     

High Temperature Thermosets With a Low Coefficient of Thermal Expansion

Summary: Polymeric thermosetting composites can be used as metal substitutes for certain applications if they possess high temperature stability in air, low coefficient of thermal expansion (CTE), and sufficient flexural strength, in combination with competitive costs. Commercial bismaleimide, bisnadimide, and cyanate ester thermosetting materials were selected due to their excellent thermal stability. Low CTEs were achieved by adding high loading levels of fused silica or silicon nitride fillers. Several optimized composites were fabricated by varying the materials, composition, and cure conditions. Characteristic composite properties, such as CTE, thermal stability, glass transition temperature (T_g), flexural strength, and filler distribution were investigated. The best system developed consists of Matrimide 5292, a commercial two‐component bismaleimide resin, filled with 75% Silbond FW100EST, and additionally reinforced with 0.5% Twaron short fibers. This composite is distinguished by a CTE around 15 ppm · K⁻¹, a T_g around 340 °C, flexural strength above 100 MPa, and attractive material costs.

Matrimid 5292 (75%)/Silbond FW100AST (24.5%), and Twaron 2 mm short fibers (0.5%). Three fibers are visible, embedded and well dispersed in the matrix.     

Development of a Portable Online Rheometer for the Characterization of PVC Melts

Poly(vinyl chloride) (PVC) is a standard polymer with a world‐wide sales quantity of more than 20 Mio. t. From a rheological point of view, PVC is much more difficult to classify than for example polyethylene. Standard thermoplastics can be plasticized by the input of thermal energy, whereas for a sufficient plastification of PVC shear energy is needed. Hence, the PVC melt properties measured with the help of standard lab‐scale rheometers are not taking the shear history into account. Therefore, the melt behavior within an extruder cannot be described. In addition, PVC melts show wall slipping effects. A new rheometer concept especially developed to characterize PVC melt is presented. The rheometer takes a representative melt stream between the screw tip and the inflow of the die. The pressure gradient of this melt stream is measured within the geometry of the rheometer. Due to this the shear history and the wall slipping effects can be accounted for. Experimental data and results are presented and the application possibilities such as the design of profile dies and the development of PVC recipes are discussed.

The portable online rheometer in the assembled state.     

Post‐Crosslinkable Blends: Reactions Between a Linear Poly(hydroxyl‐amino ether) and a Diepoxy

Summary: A thermoplastic poly(hydroxyl‐amino ether) polymer (BLOX) was blended with a diglycidyl ether of bisphenol A monomer (DGEBA). This system may be used as a crosslinkable thermoplastic. It means that it may be processed in an extruder like a classic thermoplastic, and cured by etherification reactions initiated by tertiary amine groups of the BLOX in a second step, to produce a material with good mechanical properties. In order to understand and quantify the etherification reactions occurring at high temperature (135 °C), between epoxy groups of the diepoxy and hydroxyl groups of the thermoplastic, a model system was studied based on DGEBA in excess and ethanolamine. In the model system the rate of the etherification reaction was well described by a second‐order kinetic equation. The specific rate constants and the epoxy conversion at the gel were related to the polarity of the reactive medium. The polyetherification occurring in the DGEBA‐BLOX system could also be fitted with a second‐order kinetics. A significant increase in the reaction rate was observed when using high BLOX concentrations.

     

Injection Moulding: Evaluation of Appropriate Melt Injection Points for the Gas Injection Technique

In gas assisted injection moulding the melt front advancement has a considerable effect on the gas penetration. The evaluation of an appropriate melt filling is an important step to avoid instabilities in the process sequence. Taking a sample moulded part a procedure is presented that enables the part designer to evaluate required melt and gas injection points according to the gas injection technique. Using finite element simulations, different calculations for the melt front advancement lead to the correct gate location.

Presentation of different degrees of filling for the optimised article geometry.     

Study of Reaction Between a Low Molecular Weight,Highly Functionalized Polyethylene and Hexamethylenediamine

Reactions were carried out between a low molecular weight, highly functionalized maleic anhydride‐grafted polyethylene and hexamethylenediamine in a melt blender at 150 °C for various stoichiometric ratios of functional groups. For all compositions, two peaks were observed in the mixing torque data. The appearance of the first peak, observed soon after the introduction of the reactive mixture to the melt blender, was independent of composition. The second peak was composition‐dependent. Gel content and FTIR analyses suggest that the first peak is a result of melting functionalized polyethylene and a reaction of the anhydride and amine functionalities, while the second was mainly a result of crosslinking. The time between the first and second peak defines a processing window, in which the reaction mixture is thermoplastic. Higher temperature melt processing of the thermoplastic reaction products converted these materials to thermosets. During this conversion, the progress of the anhydride–amine reaction was studied using FTIR, as well as by measuring the generation of the insoluble crosslinked material. The FTIR results reveal that the reaction between anhydride and amine moieties results in the formation of an amide intermediate, which then converts to cyclic imide at higher temperatures. The analysis suggests that the use of the FTIR anhydride absorption to assess the degree of reaction is misleading in these reactions.

     

Tremorgenic Indole Alkaloids. 10. An Improved Asymmetric Synthesis of a Tricyclic Common Intermediate

An efficient third-generation asymmetric synthesis of tricyclic lactone (+)-1, designed to serve as the common intermediate for construction of the indole tremorgens, has been developed. The major challenge was stereocontrolled introduction of the vicinal quaternary methyl groups. Our initial approaches employed enolate chemistry to install the second methyl moiety; herein we exploit instead a hydroxyl-directed Simmons-Smith cyclopropanation followed by reductive opening of the three-membered ring. The new 15-step synthesis proceeds in 8.3% overall yield, nearly an eightfold increase over the second-generation route, and is amenable to large-scale production of (+)- 1.      

Recent Progress on Nafion‐Based Nanocomposite Membranes for Fuel Cell Applications

Proton exchange membrane fuel cells (PEMFCs) have attracted tremendous attention because of their high efficiency compared to other types of fuel cells. Nafion is the most commonly used polymer for membranes used in PEMFCs. A large variety of nanoparticles of different natures and sizes can be blended with a Nafion matrix, generating a new class of nanostructured electrolyte membrane with interesting physical properties. In this paper, we discuss the recent progress in the field of Nafion‐based nanocomposite membranes. They exhibit a significant improvement in thermo‐mechanical and thermal stability as well as proton conductivity at very low filler contents. The preparation, characterization, and properties of various types of Nafion‐based nanocomposite membranes are critically reviewed, and detailed examples are summarized.

     

Photoinduced Polymerization in the Wall of Hollow Capsules

Summary: Novel light‐sensitive hollow capsules were fabricated from the small molecule 3‐sulfopropylacrylate potassium (SPA) and poly(allylamine hydrochloride) (PAH). With UV irradiation, SPA could be photopolymerized in the wall of hollow capsules. After photopolymerization the capsule size and surfaces showed pronounced differences. The capsules became much more rigid as indicated by an increase in the modulus of more than a factor of 5.

CLSM image of SPA/PAH hollow capsule emission at 554 nm, from rhodamine B after photopolymerization.     

Formaldehyde Resins Bearing Diaminodiphenylmethane Groups: Synthesis,Characterization and Properties

Summary: Novel formaldehyde resins bearing diaminodiphenylmethane groups were synthesized by the polymerization of a mixture of diaminodiphenylmethane (DDM), cyclohexanone (CHx) and o‐cresol (o‐Cz) with formaldehyde (FA) in the presence of an acid catalyst (HCl). The resins obtained were characterized by spectral, elemental and thermal analysis and used as a hardener for epoxy resins. The curing and temperature behavior of these epoxy resin/formaldehyde systems were investigated using differential scanning calorimetry and thermogravimetry techniques. The resins had good thermal stability and the activation energies of degradation reactions had values between 70–98 kJ · mol^?1.

The curing reaction of epoxy resins with the DDM/CHx/o‐Cz/formaldehyde resins.     

In‐Line Monitoring and Control of Conversion and Weight‐Average Molecular Weight of Polyurethanes in Solution Step‐Growth Polymerization Based on Near Infrared Spectroscopy and Torquemetry

Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.

Proposed control scheme.     

The Effects of Different Plasticizers on the Properties of Thermoplastic Starch as Solid Polymer Electrolytes

Plasticizers with amide groups (urea and formamide) and polyols (glycerol, glucose, and sorbitol) were used to prepare thermoplastic starch (TPS) containing NaCl salt as solid polymer electrolytes (SPE). Fourier Transform infrared (FT‐IR) spectroscopy revealed that both plasticizers and Na⁺ could form the interaction with starch, and plasticizers containing amide groups had stronger hydrogen bond‐forming abilities with starch than polyols. These interactions prevented starch molecules from crystallizing again, indicated by X‐ray diffraction (XRD). Scanning electron microscope (SEM) showed that starch granules were in a molten state and a continuous phase of TPS was formed. Among TPS as SPE, formamide‐plasticized TPS (FPTPS) had the largest elongation at break and lowest tensile stress. The conductance of TPS was sensitive to water. TPS plasticized by solid plasticizers had the higher sensitivity of the conductance to water contents at the low water contents (<0.1). The relationship of the conductance and water contents was in agreement with the second‐order polynomial correlation when water contents were below 0.45. FPTPS had the best conductance as a whole. At the medium water content (0.2), the conductance of FPTPS containing NaCl was about 10^?3 S · cm^?1.

     

Heat Induced Structure Modifications in Polymer‐Layered Silicate Nanocomposites

Summary: The success of the use of layered silicates in polymer nanocomposites, to improve physical and chemical properties is strictly related to a deeper knowledge of the mechanistic aspects on which the final features are grounded. This work shows the temperature induced structural rearrangements of nanocomposites based on poly[ethylene‐co‐(vinyl acetate)] (EVA) intercalated‐organomodified clay (at 3–30 wt.‐% silicate addition) which occur in the range between 75 and 350 °C. In situ high temperature X‐ray diffraction (HT‐XRD) studies have been performed under both nitrogen and air to monitor the modifications of the nanocomposite structure at increasing temperatures under inert/oxidative atmosphere. Heating between 75 and 225 °C, under nitrogen or air, causes the layered silicate to migrate towards the nanocomposite surface and to increase its interlayer distance. The degradation of both the clay organomodifier and the VA units of the EVA polymer seems to play a key role in driving the evolution of the silicate phase in the low temperature range. The structural modifications of the nanocomposites in the high temperature range (250–350 °C), depended on the atmosphere, either inert or oxidizing, in which the samples were heated. Heating under nitrogen led to deintercalation and thus a decrease of the silicate interlayer space, whereas exfoliation was the main process under air leading to an increase of the silicate interlayer space.

Heat induced structural modification of EVA‐clay nanocomposite under nitrogen and air.