Hartmut Widdecke

Enzymatic degradation of a model polyester by lipase from Rhizopus delemar

Abstract Enzymatic degradation of a model polyester was studied under varying conditions. Poly(trimethylene succinate) was hydrolyzed by the use of lipase from Rhizopus delemar . An enzyme assay was adjusted for the use of insoluble substrates and gave well-reproducible data. Ester bond cleavage was measured with respect to time. Comparison of ester cleavage and weight loss—a commonly used technique in the evaluation of polymer biodegradation—indicated that oligomers with an average length of five to six monomers are released from polymer bulk. Thus, weight loss as well as dissolved organic carbon measurements will not give information on real enzymatic degradation activity, because solubility properties of oligomers are superimposed. Time-dependent degradation profiles are strongly influenced by the materials surface (film or polydispers powder) as well as the addition of surfactants. The use of Triton X-45 did not assist the degradation of the insoluble substrate, as it did with commonly applied emulsions of liquid substrates. On the contrary, at concentrations above 0.5% (vol/vol), the addition of Triton X-45 inhibited enzymatic degradation to a great extent.

A rapid evaluation plate-test for the biodegradability of plastics

Solid-media agar-plate tests were investigated for their potential to evaluate the biodegradation of polymeric particles by certain strains of microorganisms. A reliable test was developed. Stable suspensions of 1-μm globules of two poly(3-hydroxyalkanoates) were prepared. These were mixed with liquified agar-agar to form turbid plates. Inoculation was carried out by plate puncturing. Seven strains isolated from sewage sludge formed clear zones. These zones were distinct, circular, and reproducible in outlook and growth. The maximal duration of single experiments was 192 h. A growth rate was defined. It allowed the classification of the polymers, and of the microorganisms used. Poly(3-hydroxybutyrate-co-valerate) was degraded faster by all the strains used than was the homopolyester poly(3-hydroxybutyrate). Strains achieving high zone growth rates generally did so on both of the polymers. This led to the assumption of similar enzymatic processes being active. Zone formation was concluded to be dependent on the amount of enzyme production plus the enzyme activity. The technique provides a means of either distinguishing the degradation abilities of a microorganisms, or the degradability of materials.

THE CONCEPT OF VARIABLE ACTIVE CENTRES IN ACID CATALYSIS PART I. ALKYLATION OF BENZENE WITH OLEFINS CATALYZED BY ION-EXCHANGE RESINS

Abstract The interaction of olefins with sulfonic acid macroporous ion-exchange resins in nonpolar medium has been investigated by measuring the acidity and the catalytic activity of the adsorbed olefin towards benzene. At low olefin concentrations a sharp maximum of reactivity was found, whereas the acidity continuously decreased with increasing olefin concentration. This substrate-inhibition has been described by the model of variable active centres: The homogeneously distributed accessible acid groups form clusters surrounding the adsorbed olefin. Increasing ratios of acid groups per adsorbed olefin operate to enhance the reactivity exponentially. In the case of more polar olefins, the maximum of reactivity is sharper and shifted to lower olefin concentrations.

Synthesis and application of new microcarriers for animal cell culture. Part II: Application of polystyrene microcarriers

In this work (Part II) the application of new polystyrene based microcarriers in cell culture technology is demonstrated. Carriers with a variety of surface modifications were tested as a growth support for cell line BHK 21. The growth behavior of the cells and cell to surface attachment were compared to Cytodex 3 (Pharmacia), which was used as a reference carrier. To select carriers with growth supporting surfaces, broad screening in petri dish experiments was carried out. Candidates with the highest growth rates were investigated in spinner flash experiments in further detail. Polystyrene carrier with a surface modification like triethylamine, maltamine or N-methylglucosamine were able to support growth as good or better as the reference carrier Cytodex 3. Economies of ingredients and ease in laboratory handling could make amine-modified polystyrenes a competitive alternative to currently commercially available microcarrier types.

Synthesis and application of new microcarriers for animal cell culture. Part I: Design of polystyrene based microcarriers

In this work (Part I), surface modified styrene polymers as new microcarrier material for animal cell culture were extensively investigated. The first synthesis steps--carried out by chloromethylation, sulphonation and nitration of the polystyrene matrix--resulted in precursors with a defined surface layer thickness. The obtained hydrophobic bulk phase showed a limited absorption of hydrophilic media components compared to polysaccharides matrices like dextran. By varying reaction conditions for microcarrier synthesis and/or by using similar styrene type polymer matrices like polyvinyltoluene, the specific density (1.028-1.05 g/cm3) of the microcarrier matrix was adjusted without problems. Chemical varying of the microcarrier surface by reaction of the precursors with different amines, saccharides or proteins led to new microcarriers with optimal conditions for cell adhesion and cell growth. All biological investigations were carried out with a BHK 21 (c-13) cell line. Detailed results will be discussed and summarized in Part II of this work.

Measurement of acidity of polymeric solid acids

Abstract Acidity measurements using Hammett indicators have been applied to macroporous sulfonic acid ion-exchange resins in nonpolar media. The acidity was varied by partial ion-exchange. It has been proven that the adsorption of the indicator molecules is reversible in the case of a thermally pretreated resin. From the measurement of the adsorption data, the ionization ratio of the indicators can be calculated and correlated to the reactivity in the alkylation of benzene with propene and to the degree of ion-exchange. Using these correlations, a relative acidity scale can be defined. The accessibility of acid groups in different solvents must be determined as a prerequisite for the application of the theory developed in this study.

Sulfonic acid ion-exchange resins as catalysts in nonpolar media: II. Influence of conditioning methods on the acidity and catalytic activity

Abstract The behaviour of macroporous sulfonated styrene-divinylbenzene copolymers has been investigated in relation to their acidity and catalytic efficiency in the alkylation of benzene with propene. In order to optimize catalyst activity, the following separate parameters have to be taken into account: Adsorbed water lowers the catalytic activity, but after an induction period the poisoning effect of water is at least partially offset by the interaction of the sulfonic acid groups with the olefin. The optimal drying temperature is 100°C; higher temperatures cause a sharp decrease in catalyst acidity and therefore lower catalyst activity. In addition, the perfusion of the dried resin with benzene can produce a considerable decrease in catalyst activity. The deactivation caused by elevated drying temperatures and by interaction with benzene is discussed in terms of their effect on the flexibility of the polymer backbone.

Sulfonic acid ion-exchange resins as catalysts in nonpolar media: I. Drying of the catalyst

Abstract The retention of adsorbed water upon drying of sulfonated macroporous styrene-divinylbenzene copolymers in vacuo was investigated gravimetrically and by Karl Fischer titration. The residual water content θ w decreased with increasing degree of crosslinking and was related quantitatively to the temperature, pressure and duration of drying. The increase of the drying temperature was limited with respect to the thermal stability of the resins, and the reduction of θ w was effective only down to certain values θ w . θ w was found to depend on the degree of proton exchange by K + and Ca 2+ in different ways and to decrease in the sequence La 3+ ≈ Ca 2+ > H + > K + .

Structure-breaking effect of metal ions influencing the acidity of an anhydrous acid

Abstract A model is proposed describing the acidity of an anhydrous acid whose protons are partially exchanged by different metal ions. The acidity is related to a defined structure-breaking effect of the ions. The ions cause a decrease in the proton activity Δ log a H+ which is related to the degree of exchange x according to Δ log a H+ = A [ K 0 -log( x /(1- x ))] where K o is a constant depending on the degree of self-ionization of the pure acid. The parameter A is proportional to the radius and inversely proportional to the valence of the metal ion. The model is applied to a sulfonic acid ion-exchange resin partially exchanged by alkali and alkaline-earth ions. The acidity is measured both using kinetic data of an acid-catalyzed model reaction and by the adsorption equilibria of basic indicators.