Compositions comprising starch and/or modified starch and plasticizers

#The invention relates to compositions which comprise starch and/or modified starch and plasticizers and also, if desired, other additives, and which can be processed to give shaped articles, in particular to give shaped biodegradable articles, and to the use of the compositions for producing shaped articles.

#Constantly increasing awareness of the environment, together with continuing increases in the strictness of regulations relating to waste disposal or recycling, have led to a marked increase in efforts to use biodegradable materials for producing shaped articles. In addition to this, ever increasing efforts are being made to use, wherever possible, materials based on renewable raw materials rather than those based on mineral oil. In many cases substances from natural sources are also less physiologically hazardous.

#Starch and modified starch, alone or else mixed with other polymers, in particular with biopolymers, are renewable raw materials of constantly increasing importance, especially for producing shaped articles, such as foils or films. There are many problems here for processors. For successful shaping of starch, modified starch or else mixtures with other polymers, very intimate mixing, i.e. homogenization, of the components is required, in particular if the materials are to be processed thermoplastically. It is also important that during shaping the mixture has been sufficiently plasticized, in order to avoid having to accept excessively high shaping temperatures and the associated decomposition of the components. The shaped articles, furthermore, should not only have good biodegradability but also have a very homogeneous internal structure and good mechanical properties, such as strength and elasticity. In particular, a requirement for most applications is that brittleness and abrasion are very low. The plasticizer should also be environmentally friendly, i.e. biodegradable and physiologically nonhazardous.

#Preparation of a Thermoplastic Molding Composition Made From Potato Starch and Gluconolactone at Basic pH

#The materials are prepared in a kneading assembly (IKA Duplex kneader). The kneading assembly is heated to 140° C. 150 g of potato starch (Toffena from Südstärke) are added while the kneading assembly is in its operating condition. 22.5 g of δ-gluconolactone (15% by weight) are dissolved in about 70 g of deionized water (pH=7) (pH=from 3 to 4) and the pH value is set to 8 by adding 1 mol of NaOH solution. The total amount of water is set to 75 g by adding more deionized water. The pH is checked using a WTW (pH 538) pH meter (calibration against phosphate buffer). The solution is slowly transferred in a fine stream into the starch in the kneader. This is followed by kneading until the material becomes glassy (for about 20 to 30 minutes). Thermoplastification takes place with the cover closed, but it may be removed for short periods for observation. The kneader is stopped, the feed equipment is removed and the molding composition is removed while still hot. The molding composition is glassy, viscous and flexible. After cooling, the thermoplastic material can be further processed. The molding composition becomes increasingly hard as—it cools, but retains a certain flexibility.

#Preparation of Other Thermoplastic Molding Compositions From Potato Starch and Gluconolactone at Basic pH