Extrusion Coating of Paper with Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)—Packaging Related Functional Properties

Abstract

Taking into account the current trend for environmentally friendly solutions, paper coated with a biopolymer presents an interesting field for future packaging applications. This study covers the application of the biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) on a paper substrate via extrusion coating. The intention of this study is to analyse the effect of a plasticiser on the processability (melting point, film thickness) and the final properties (crystallinity, elongation at break) of PHBV. Up to 15 wt.% of the plasticisers triethyl citrate (TEC) and polyethylene glycol (PEG) were used as additive. The processing (including melt flow rate) as well as the structural properties (melting and crystallisation temperature, surface structure by atomic force microscopy (AFM), polarisation microscopy, scanning electron microscopy (SEM)), mechanical properties (elongation at break, tensile strength, elastic modulus, adhesion), and barrier properties (grease) of these blends and their coating behaviour (thickness on paper), were tested at different extrusion temperatures. The melting temperature (Tm) of PHBV was reduced by the plasticisers (from 172 °C to 164 resp. 169 °C with 15 wt.% TEC resp. PEG). The minimal achieved PHBV film thickness on paper was 30 µm owing to its low melt strength. The elastic modulus decreased with both plasticisers (from 3000 N/mm2 to 1200 resp. 1600 N/mm2 with 15 wt.% TEC resp. PEG). At 15 wt.% TEC, the elongation at break increased to 2.4 length-% (pure PHBV films had 0.9 length-%). The grease barrier (staining) was low owing to cracks in the PHBV layers. The extrusion temperature correlated with the grease barrier, mechanical properties, and bond strength. The bond strength was higher for films extruded with a temperature profile for constant melt flow rate at different plasticiser concentrations. The bond strength was max. 1.2 N/15 mm. Grease staining occurs because of cracks induced by the low elongation at break and high brittleness. Extrusion coating of the used specific PHBV on paper is possible. In further studies, the minimum possible PHBV film thickness needs to be reduced to be cost-effective. The flexibility needs to be increased to avoid cracks, which cause migration and staining.

A review on cationic starch and nanocellulose as paper coating components

“…Most of the recent research on coating solutions is conducted towards truly biodegradable paper. Poly-3-hydroxybutyrate, poly(lactic acid), casein, beeswax, chitosan with palmitic acid, and poly(3hydroxybutyrate-co-3-hydroxyvalerate), for instance, have been proposed as green alternatives to conventional plastics [48,49,53]. These materials, nonetheless, are less economically feasible than their petrobased counterparts.…”

Improvement of Paper Resistance against Moisture and Oil by Coating with Poly(-3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and Polycaprolactone (PCL)

“…All the coatings improved base paper resistance (resistance ranging between 0 and 10 min), but performances were not comparable with fluorinated and polyethylene-coated papers, which did not show any failure after 72 h. Resistance times recorded for PHBV coated papers were generally lower than 20 min; only PHBVpeg5 showed resistance ranging between 40 and 60 min. The few studies available in literature report variable grease resistance data and ascribe this variability to the presence of cracks or to lack of uniformity in the material [23]. PCL coated samples showed in all cases a resistance of more than 4 h, but less than 12 h, except one sample showing a higher resistance between 12 and 24 h. As shown in Figures 7 and 8, fluorinated paper resulted far more hydrophobic than other samples, possibly because of the epichlorohydrin treatment.…”

“…Other authors [23,31] characterized PHBV paper coatings by SEM, but the different techniques, polymers and base support used do not allow a reliable comparison of results.…”

“…The addition of plasticizer seemed to progressively mitigate this phenomenon (Figure 2d-f). In both PHBV with PEG at 10% and PCL with PEG at 10% and 20% coatings (shown at 1500× Other authors [23,31] characterized PHBV paper coatings by SEM, but the different techniques, polymers and base support used do not allow a reliable comparison of results.…”

Reactive Water Vapor Barrier Coatings Derived from Cellulose Undecenoyl Esters for Paper Packaging

“…Although the ubiquitous plastic packaging materials have excellent moisture barrier performance, they result in environmental, energy and health problems [3,4]. In this case, paper packaging materials have emerged due to their biodegradability, recyclability, renewability, flexibility, low cost, lightweight, good mechanical strength, and printability [5,6]. However, on one hand, the hygroscopicity is the intrinsic weakness for paper packaging materials due to the abundant hydroxyl groups; on the other hand, the existing porous structure of paper itself also caused its poor barrier performance.…”