Influence of the filler material on the thermal stability of one‐component moisture‐curing polyurethane adhesives

Filler materials are part and parcel for the adjustment of adhesives, in particular, their rheological and mechanical properties. Furthermore, the thermal stability of adhesives can be positively influenced by the addition of an expedient filler, with inorganic types common practice in most cases. In this study, one‐component moisture‐curing polyurethane adhesives for engineered wood products based on isocyanate prepolymers with different polymer‐filled polyether polyols were investigated with regard to the filler's potential to increase the thermal stability of bonded wood joints. The property changes due to the addition of fillers were determined by means of mechanical tests on bonded wood joints and on pure adhesive films at different temperatures up to 200°C. Additional analyses by atomic force and environmental scanning electron microscopy advanced the understanding of the effects of the filler. The tested organic fillers, styrene acrylonitrile, a polyurea dispersion, and polyamide, caused increases in the cohesive strength and stiffness over the whole temperature range. However, the selected filler type was hardly important with regard to the tensile shear strength of the bonded wood joints at high temperatures, although the tensile strength and Young's modulus of the adhesive films differed over a wide range. Prepolymers with a lower initial strength and stiffness resulted in worse cohesion, in particular, at high temperatures. This disadvantage, however, could be compensated by means of the filler material. Ultimately, the addition of filler material resulted in optimized adhesive properties only in a well‐balanced combination with the prepolymer used. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Online LC-NMR – From an expensive toy to a powerful tool in polymer analysis

The present review is the latest and most comprehensive summary on advanced developments in the field of LC-NMR of polymers. Different from LC-NMR applications in biochemistry, pharmaceutics and other fields that target at the identification and quantitative determination of specific molecules, LC-NMR of polymers is aimed at the analysis of the molecular heterogeneity of complex macromolecular mixtures. Using LC-NMR the distributions in molar mass, chemical composition and molecular microstructure can be addressed. Although LC-NMR is the most expensive version of LC-spectroscopy couplings, it provides a wealth of qualitative and quantitative information that cannot be matched by any other coupling technique. The review presents the latest results on the coupling of NMR with SEC, HPLC, 2D-LC and field-flow fractionation (FFF) for the analysis of oligomers, copolymers and polymer blends. The given examples clearly prove that LC-NMR of polymers has matured and is now a powerful tool in advanced analytical polymer science.     

Phospholipases A<Subscript>1</Subscript> from <Emphasis Type="Italic">Armillaria ostoyae</Emphasis> Provide Insight into the Substrate Recognition of α/β-Hydrolase Fold Enzymes

Four enzymes with phospholipase A₁ (PLA₁) activity were purified from the fruiting bodies of the basidiomycete Armillaria ostoyae. The enzymes (PLA₁-1, -2, -3 and -4) showed similar isoelectric points (4.3, 3.9, 4.0 and 4.0) and apparent molecular masses in the range of 35–47 kDa. Mass spectrometric analyses of proteolytic fragments revealed sequences homologous to α/β-hydrolase fold enzymes. The enzymes share one conserved region with fungal phospholipases B and the active site sequence with bacterial esterases and PLA₁s. PLA₁-1 cleaves phospholipids and lysophospholipids with an optimum activity at pH 5.3. In contrast, PLA₁-2, -3 and -4 are characterized by broad pH optima in the slightly acidic to neutral range and are additionally capable of hydrolyzing mono- and diglycerides as well as fatty acid methyl esters. All enzymes favor glycerol-based lipids with a single medium-sized fatty acid moiety in the sn-1 position but show reduced activity towards the corresponding 1,2-diacyl derivatives with bulky long-chain or inflexible saturated fatty acid moieties in the sn-2 position. The enzymes prefer zwitterionic phospholipid substrates and are unable to hydrolyze triglycerides. From the selectivity of these broad-spectrum α/β-hydrolase fold enzymes towards the different classes of their substrates a regiospecific steric hindrance and a head group recognition are concluded.     

Photopolymerized low‐surface‐energy coatings based on a novel fluorinated ether acrylate

The synthesis, characterization, and polymerization of a perfluoroalkyl ether substituted methacrylic acid (C8F7) were investigated. C8F7 was photopolymerized at different temperatures, higher double‐bond conversions being achieved at higher polymerization temperatures. The polymerization rates were fast in comparison with those of typical methacrylate esters. Thermogravimetric analysis of the obtained polymers showed thermal stabilities up to 270–290°C. The initial degradation at 200°C involved the loss of water and the partial loss of the perfluoroalcohol via the intramolecular formation of anhydride and lactone groups. The surface properties of coatings obtained with C8F7 coatings on various substrates were evaluated with water and hexadecane contact‐angle measurements, which confirmed that low‐surface‐energy polymeric coatings were obtained. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3301–3314, 2004     

Nitroxide‐Controlled Grafting by an Insertion Mechanism using a Polymerizable N‐Oxyl

Summary: The polymerizable nitroxide 4‐acryloyloxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (AOTEMPO) was utilized in a two step polymerization to prepare alkoxyamine‐functionalized backbone polymers. These backbones were then used as initiators for stable free‐radical graft polymerizations in bulk at 125 °C. The products were cleaved into their linear components by reaction with L ‐(+)‐ascorbic acid allowing a reproducible analysis of the molecular weights. The influences of the backbone concentration and the graft density on the polymerization were investigated. Graft polymers purely consisting of styrene were produced as well as polymers with a backbone based on 2‐ethoxyethyl acrylate (EOEA). In addition a graft polymer with block copolymer side chains was prepared by extending a preformed graft polymer. In all cases the controlled course of the reaction was confirmed by the linear increase of the molecular weights over conversion and the low polydispersities of the products.

Structure of an extended graft copolymer.     

Crystallization of Nano‐Calcium Carbonate: The Influence of Process Parameters

Precipitated calcium carbonate was synthesized by carbonation of calcium hydroxide in the presence and absence of ultrasound (conventional stirring) at atmospheric as well as at elevated pressures and different initial concentrations of Ca(OH)₂. Spherical morphology of the formed calcite was favored at high Ca(OH)₂ concentrations and low CO₂ pressures. The presence of ultrasound did not show any influence on the reaction rate in case of efficient mixing. A small increase of the reaction rate was observed at lower CO₂ pressures. Elevated pressures in combination with ultrasound did not lead to notable changes of reaction rate or particle morphology.     

Populationsbilanzmodellierung mit einem Mehrphasen‐CFD‐Code und vergleichende Visualisierung

The Euler‐Euler multiphase approach multiphaseEulerFoam is extended by implementation of several population balance models to describe the variation of the dispersed phase bubble size. The different models are compared with each other and with experimental data. A new approach is developed, which allows, in addition to the representation of the bubble size, an accurate visualization of the bubble shape based on the Eötvös and Reynolds number as well as position probability and number of bubbles and therefore simplifies the comparison between simulation and experiment.     

Synthesis and Characterization of Poly(ethylene glycol) Methacrylate Based Hydrogel Networks for Anti‐Biofouling Applications

A series of hydrogels based on poly(ethylenglycol) methyl ether methacrylate (PEGMEMA) is synthesized using macromonomers of three different molecular weights, in combination with varied degrees of chemical crosslinking. The effects of PEGMEMA, initiator, and crosslinker concentrations on gel yield and swelling properties are studied. In addition, the chemical structure of the gels is characterized by FTIR and solid‐state NMR spectra. The swelling and rheological behaviors of hydrogels as well as protein partitioning into the gels are discussed in terms of the network mesh size. Low protein sorption and bacteria deposition tendencies indicate that PEGMEMA‐based hydrogels could be highly beneficial for uses as fouling‐resistant materials, for instance, as protective coatings for desalination membranes.

     

Thesis Summary: Theoretical and Experimental Investigation of a Solar-Biomass Hybrid Air Heating System for Drying Applications

The overall objective of this research was to design, develop, and investigate the performance of a renewable energy-based (solar-biomass) hybrid air heating system. The system consists of an unglazed transpired solar collector (UTC), a rock bed thermal storage, and a biomass gasifier stove with heat exchanger, to supply hot air at a required temperature and flow rate for a daily load fraction exceeding 90%. From a review of literature, an air heating system aimed at reducing the weather dependency and improving the temperature and flow rate stability without a conventional back-up heater was designed. Among the various types of solar collectors, thermal storage, biomass stoves, and heat exchangers that are generally used, specific designs were chosen and analyzed. Based on the analyses, individual components of the air heating system were designed and developed. The components were coupled, and detailed experimentation was carried out on the integrated system.     

Rheological studies on PNIPAAm hydrogel synthesis via in situ polymerization and on resulting viscoelastic properties

Bulk poly(N-isopropylacrylamide) hydrogels were prepared via free radical polymerization. Two different initiation methods were studied: redox- and photoinitiation. It was demonstrated that the desired final properties of resulting hydrogels, i.e., high monomer conversion (>95%) and adjustable swelling were only obtained by selecting best suited initiation conditions. For redox polymerization, this was achieved by tuning the ratio of accelerator N,N,N′,N′-tetramethylethylenediamine to initiator ammonium persulfate. The key parameters for achieving optimum photopolymerization conditions were photoinitiator concentration and UV irradiation time. With help of in situ rheological measurements, optimum conditions could be further verified and quantified by monitoring the liquid-to-gel transition. Overall, photoiniated crosslinking copolymerization was postulated to offer better options for in situ preparation of tailored functional hydrogels, in particular for the integration of smart soft matrices within membrane pores or other microsystems via a rapid reaction. Rheology was also used to investigate the hydrogel after ex situ preparation, revealing “perfect” soft-rubbery behavior. A good correlation between the mesh sizes determined from swelling and rheology was also found. In conclusion, rheology has been found to be a powerful tool because it provides valuable data on polymerization and gelation kinetics as well as information about the hydrogels microstructure based on their viscoelastic character.