bioresources. com
PEER-REVIEWED REVIEW ARTICLE
PROSPECTS Barrier materials have an important role in different types of packaging applications, considering the protection from the environment and shelf life that they provide. Conversely, in some instances, the barrier material protects the environment from the product. Several barrier materials in today’s industry are manufactured either from oil resources or metals. Driven by both the increase in environmental awareness, as well as the resource scarcity, novel and environmentally benign alternatives have been sought. This review covered wood and fermentation-based materials, which display interesting barrier properties and offer a potential for utilization in packaging. Wood-based products have received great attention in a wide variety of fields. Hemicellulose-based barriers have been reported to display resistance against oil, grease, aroma and oxygen. Moreover, hydrophilic hemicelluloses offer promising barrier properties, and are easily modified. For polysaccharides streams, the main challenges include their mechanical properties, processability, and low water resistance. A relatively weak heat stability and narrow processing window may be challenging, and lower running speeds may be needed compared to oil based alternatives. Also, the adhesion may be challenging, depending on the substrate. Derivatives of cellulose render it soluble in various solvents that are widely used in industry. Their thermal properties and facile application on surfaces are great advantages. However, a more detailed discussion is needed, especially if focused on processing of eco-friendly barrier films at speeds relevant to industrial production. A few essential variables are critical when considering cellulose derivatives and structure-property-process relationships for upscaling novel cellulose derivatives. These variables include the degree of substitution that is linked with water vapor permeability. The reaction conditions of cellulose derivatives regulate their DS, DP, and final properties, which include film-forming and barrier properties. There is interest for developing novel cellulose derivatives, due to a trend aiming for methods to replace petroleum-based packaging materials. Firstly, there have been suggestions for blends with other materials that compensate the poor WVP and enhance other barrier properties. Simultaneously, novel cellulosic solvents may bring promise, together with homogeneous modification methods, for increased regioselectivity leading to improved and more end- use-specific properties of the cellulose derivatives. The interest towards lignin has been based on its availability and cost as well as its possibilities for chemical modification. Considering potential barrier applications, the properties of interest in lignin include its antioxidant behavior and UV-light resistance. However, challenges with technical lignins involve its poor film-forming properties and dark color. There have been several publications covering heat treatment of nanocellulose. The crystallinity is important for oxygen permeability, whereas material density is decisive for water vapor permeability. In addition, the combination of hydrophobic, thermoformable matrices with nanocellulose is under study, and some promising solutions exist regarding compatibility, but also challenges, such as the low WVP of nanocellulose. The economic aspects and upscaling potential in nanocellulose production has been reported, and a few nanocellulose-containing end-use products are already commercialized. Nevertheless, several challenges remain to be resolved prior to large- scale industrial production, such as the hygroscopic tendency of nanocellulose to absorb moisture from its surroundings, swelling, and others.
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Helanto et al. (2019). “ Bio-based barriers ,” B io R esources 14(2), Pg #s to be added.
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