L.P.B.M. Janssen’s research while affiliated with University of Groningen and other places

The use of a combined stirrer-torque meter allows for monitoring viscosity during polymerizations and other reactions, much faster and more continuous than off-line viscosity measurements. This method was applied in previous research about the grafting of acrylic acid onto cassava starch using Fenton’s initiator. In this article the method is used to assess the effect of Fenton's initiator on gels of cassava starch in the absence of the monomer. The intention here is to activate the starch selectively first, which could improve graft selectivity. The interaction of a redox graft copolymerization initiator with starch gels when there is no monomer in the system yet, is hardly ever addressed in grafting literature. Remarkably, the present experimental study shows a rapid viscosity decrease of the starch gel, in the order of 70% in less then 2 minutes, at conditions reflecting graft copolymerization. This result must be considered a major setback for the application of pre-initiation. Torque measurement also allows to identify the important steps in the reaction of Fenton's reagent with starch without the need to do other, more intensive analyses on the chemistry. For example, it could be concluded that the second stage of Fenton's reaction, the slower decomposition of hydrogen peroxide by Fe³⁺ ions, accounts for another 20% loss of the original gel viscosity but over a longer period, some 30-60 minutes. Possible further decrease over a longer period is too slow or small relative to the measuring accuracy of the torque meter. FTIR analyses show the occurrence of peaks at 1730-1740 cm⁻¹ in starch which has been subjected to reaction with Fenton's. These peaks are in the range of the vibrational frequencies associated to C=O bonds, that are not present in the original starch. This provides at least a strong indication for oxidative degradation of the starch chains.

Literature data on the rheological behavior of a reaction mixture during the graft copolymerization of acrylic acid onto gelatinized starch are scarce. Yet, such information is important for process design. In this work, continuous torque recording was found to be a suitable method to monitor the apparent viscosity. Reactions were performed in a bench scale reactor at ambient conditions with the monomer to starch ratio as the main variable. Apparent viscosity of the reaction mixture increased rapidly, which could be fitted with good accuracy with a first order exponential growth model. The maximum viscosity of 18 Pa⋅s was seen at the intermediate monomer to starch ratio of 1.0, a phenomenon that is in accordance with literature data. Starch thixotropy is influenced by the grafting of poly-acrylic acid, until it has almost disappeared at the highest monomer to starch molar ratio of 2.0. POLYM. ENG. SCI., 2017.

Chemical engineering has made a substantial contribution to the improvement of the environment during the last decades. Many processes have become more sustainable and harmful waste streams are minimised. However, considerable improvement of sustainability can still be obtained in product engineering and design. Especially the aspects that are important at the end of the life cycle of the product can be improved considerably. A priority list for the design of more sustainable products is presented and illustrated with examples of daily chemical engineering practice.

Graft copolymers of starch with acrylic acid are a promising green, bio based material with many potential applications. The grafting of acrylic acid onto cassava starch in an aqueous medium initiated by Fenton's reagent has been studied. Common grafting result parameters are add-on (yield) and graft efficiency (selectivity). However, the analysis of the reaction products and an accurate determination of these parameters stand or fall with a complete separation of the entangled but ungrafted homopolymer from the grafted product. Therefore, this separation is the core of the newly developed analytical procedure. An appropriate solvent has been selected with dedicated testing from the range methanol, ethanol, acetone, dioxane, 2-propanol, and 1-propanol. Acetone showed the best performance in many respects. It has a high dissolving power for the homopolymer, as well as the highest yield of precipitation for the starch derivatives and it is the most economical in use. After the successful separation, the precipitated graft copolymers could be analyzed quantitatively by nuclear magnetic resonance. The liquid with homopolymer and unreacted monomer was analyzed by high pressure liquid chromatography. Proof of grafting has been found by FTIR and TGA analyses. The mass balance calculation shows a systematic error which appears fairly consistent: 18.0±2.5wt%. This was used as a correction factor in the calculation of the grafting parameters but more importantly, it means that the method we developed has a high level of repeatability, in the order of 97%.

Thermoplastic starch (TPS) as fully biodegradable biopolymer appeared to be one of the most useful and promising materials for packaging purpose. To obtain TPS thermal and mechanical processing should disrupt semi-crystalline starch granules. As the melting temperature of pure starch is substantially higher than its decomposition temperature, there is a necessity to use plasticizers, e.g. a glycerol.Various blends of potato starch mixed with glycerol were extrusion-cooked to obtain different range of TPS pellets, then processed using film blowing and injection molding techniques. Starch modification under high temperature, glass transition temperature, visco-elastic properties of TPS samples (DMTA), the storage modulus E′ and loss modulus E″ were evaluated for several frequencies. The mechanical properties, the texture and the structure of the obtained materials were measured using standard methods.