Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
Food packages containing products such as fruit juices, coffee, snacks and spices need to have barriers that can prevent oxygen, aroma substances and grease to diffuse through the packages in order to maintain or extend a certain quality of the product. Today those barriers consist of aluminium and ethylene-vinyl alcohol (EVOH) plastics, based on petroleum. The prices for these materials are raising and the growing shortage of fossil fuels eager the needs for an alternative to existing barriers.
It has been shown that hemicelluloses can be treated to form films with low permeability to oxygen, greases and aroma substances. Hemicelluloses are one of the must abundant biopolymers and can be isolated from for example annual plants. Isolation of hemicelluloses is preferably performed with alkali extraction, by recycling and reusing of alkali, the production process could be more cost effective and less burdensome for the environment. The alkali is separated from the hemicelluloses by ultrafiltration.
The study was divided in two parts. The purpose of the first part was to examine how the oxygen permeability of the barrier was affected when alkali was recovered directly from an effluent waste stream from the ultrafiltration and with the addition of some fresh alkali reused for extraction in another batch. The second part of the study was dedicated to investigate how nanofiltration membranes could be used to recover pure alkali from the effluent stream. The membranes studied were NF97, NF99 and NF99HF, all three manufactured by Alfa Laval. By varying pressure, flow and temperature it was investigated which membrane that gave the highest fluxes through the membrane, the permeate fluxes, and highest concentrations of alkali.
Recycling alkali directly from one batch to the following could not be proved to affect the oxygen permeability negatively, although the concentration of the recovered alkali was rather low. The nanofiltration membrane that gave the highest permeate fluxes was NF99 while NF97 gave the highest concentrations of alkali.
2009. , 42 p.