Abstract
This study investigates chemical grafting with fatty acid chlorides as a method for the surface modification of hydrophilic web materials. The resulting changes in the water repellence and barrier properties were studied. For this purpose, different grades of polyvinyl alcohol (PVOH) were coated on regenerated cellulose films (“cellophane”) and paper and then grafted with fatty acid chlorides. The PVOH grades varied in their degree of hydrolysis and average molecular weight. The surface was esterified with two fatty acid chlorides, palmitoyl (C16) and stearoyl chloride (C18), by chemical grafting. The chemical grafting resulted in water-repellent surfaces and reduced water vapor transmission rates by a factor of almost 19. The impact of the surface modification was greater for a higher degree of hydrolysis of the polyvinyl alcohol and for shorter fatty acid chains. Although the water vapor barrier for palmitoyl-grafted PVOH was higher than for stearoyl-grafted PVOH, the contact angle with water was lower. Additionally, it was shown that a higher degree of hydrolysis led to higher water vapor barrier improvement factors after grafting. Furthermore, the oxygen permeability decreased after grafting significantly, due to the fact that the grafting protects the PVOH against humidity when the humidity is applied on the grafted side. It can be concluded that the carbon chain length of the fatty acid chlorides is the limiting factor for water vapor adsorption, but the grafting density is the bottleneck for water diffusing in the polymer.
Highlights
The currently widely applied principle of sustainability, which is important in today’s world, covers products for fast moving consumer goods (FMCG), such as packaging materials
The increase in OP when the relative humidity is increased is a huge drawback for using polyvinyl alcohol (PVOH) as an oxygen barrier material, in particular for wet foods and foods that are stored at high relative humidity
The chemical grafting performed in this study resulted in water-repellent surfaces and reduced the water vapor transmission rates by a factor of almost 19
Summary
The currently widely applied principle of sustainability, which is important in today’s world, covers products for fast moving consumer goods (FMCG), such as packaging materials. The utilization of biopolymers in packaging applications is increasing, with biopolymers substituting or complementing conventional fossil-based polymers [1,2,3,4,5,6,7,8]. Biopolymers are defined as being based on renewable resources and/or being biodegradable [9]. The most available renewable raw material is cellulose, which is mainly acquired from wood, cotton and annual plants [1]. The properties of cellulose-based fabrics (textiles) and layers (paper, cardboard, corrugated board) are strongly influenced by the macroscopic shape of the cellulose fibers and the strong intramolecular and intermolecular hydrogen bonds [10]. Cellulose-based materials have several advantages: high availability, printability, good mechanical properties, high thermal stability and relatively low costs
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