Exploring the interactions between starches, bentonites and plasticizers in sustainable barrier coatings for paper and board

Abstract

Effective food packaging is a major factor in the current global drive to minimise food waste. Starch is an excellent oxygen barrier for packaging but it is brittle and moisture sensitive. The addition of layered minerals and plasticizers can significantly improve the moisture barrier and flexibility of the resulting composite. Some combinations of starch and plasticizer are incompatible but our results show that the addition of bentonite ensures the formation of coherent starch films with much improved moisture barrier regardless of the starchplasticizer compatibility. It was clearly demonstrated that improvement of the moisture barrier was critically dependent on the layer charge of the bentonite used. Starch was readily accommodated in the interlayer space of bentonites with a layer charge of < 0.4 electrons per formula unit but was not adsorbed if the layer charge was above this value. Starchbentonite-plasticizer coatings prepared using bentonites with the lower layer charge routinely produced higher barriers to water vapour. The water vapour transmission rate (WVTR) of the base paper was reduced from 780 to 340 ± 20 g m 2 day-1 when coated with starch alone. This was further reduced to 48 or 66 g m 2 day-1 if glycerol or lower charge bentonite, respectively, was added to the starch. Optimised coatings of starch-lower charge bentoniteplasticizer provided WVTR values of ≤ 10 g m 2 day-1 whereas WVTR values for comparative coatings prepared using the higher charge bentonites were three to four times higher (35 ± 7 g m 2 day-1). Scanning electron micrographs provided clear evidence for the presence of 60 nm thick supramolecular layers formed from starch-bentonite-plasticizer in the samples 2 coated on either glass or paper. The WVTR values for these low-eco footprint coatings are competitive with proprietary coatings prepared using petroleum derived resins.

A review on cationic starch and nanocellulose as paper coating components

“…William R. Collings and Harold C. Kelly developed greaseproof paper by coating with methylcellulose, sodium cellulose glycolate and hydroxyethylcellulose, besides plasticizers like sorbitol, ethyl sorbitol and glycerine [189]. Plasticizers such as bentonite along with starch [190], starch-silver nanoparticles [191], soybean oil-based coating materials plus other polymer emulsions [192], curdlan and chitosan [193], xylans [194], and nanocrystalline cellulose-AKD emulsion [43] were also tested in paper coating formulations to improve both barrier and mechanical properties.…”

Characterization and properties of nanocellulose-enhanced pulp-molded lunch boxes

“…2(d) is the SEM photo of the enhanced box spin-coated with nanocellulose functional materials. The surface is very smooth, and the morphology of plant fibers cannot be seen, indicating that the nanocellulose functional materials have uniformly filled the pores of the fibers, and formed a coating layer on the surface [7][8].…”

Hybrid paper sheets with improved barrier properties

“…WFP was selected as the control sample of the study and its properties were also tabulated. In literature, usually platelet shaped clays [17][18][19][20][21][22], and colloidal or agglomerated particles [23][24][25][26][27][28][29][30] are used to enhance the barrier properties of the coated substrates against water or air. Since the aim of the study was to enhance the barrier properties of the samples as much as possible, no sample with just PDMS coating layer was tabulated.…”