PARTICULARIDADES EN LA ENTREGA DE ALGUNOS PRODUCTOS

In the barrier research, new coating materials for achieving grease resistance of paperboard in packaging applications were developed. One aim was to obtain the coating materials as water-based dispersions. Six different types of bio-based derivatives were developed and tested during the project. These were modified GGM (Åbo Akademi University), modified xylan (VTT), TOFA esters and TOFA alkyd acrylates (University of Helsinki), dialdehyde cellulose alginates (University of Oulu) and cellulose- copolymer blends (Aalto University). Additionally, the barrier coatings were up-scaled from lab to pilot scale and the multi-layer paperboard packaging structures with good grease barrier properties were demonstrated. More than 60 derivatives were tested during the project. Centralized coating tests were performed at VTT facilities (Figure 2) and pilot coated samples were further sent to TUT for extrusion coating and LUT for conversion into tray form.

Sample characterisation was also conducted in a centralized testing environment, including grease, water vapour transmission (WVTR) and oxygen barrier (OTR) measurements.

When considering the grease barrier, the most promising coatings are cellulose-copolymer blends (CePE) and hydroxypropylated xylan coatings. Figure 3 shows the results for the best candidate of these two (CePE and xylan) as well as TOFA hybrid latex (HL) derivative families as normalized to 20 µm thickness. In grease resistance measurements our target was to attain extended resistance, i.e. high values when measured in days (y-axis) as well as low water vapour and oxygen transfer rates (WVTR and OTR, respectively). The blue circle represents the combined target value

area with respect to 3a) grease resistance and water vapour barrier or 3b) oxygen and water vapour barrier.

Regarding the cellulose-copolymer blends (CePE), grease resistance of over 65 days was obtained with a dissolved cellulose/ poly(ethylene-co-acrylic acid) blend with a 95/5 polymer/polymer ratio. After dispersion coating, the best OTR achieved was 130 cc/ (m2_{d bar); however after PE extrusion OTR the} value was as low as 2 cc/(m2_{d bar). The WVTR} target was also achieved. In this group, the blending capability of commercial co-polymers with alkaline aqueous cellulose solution was studied and the mixing procedure and blend compositions developed. This was done in order to obtain the best morphology of the solutions/ suspensions for the coating trials.

TOFA-based hybrid latexes (HL) were synthesized and applied on paperboard and water and grease barrier properties were analysed. Good water and water vapour barrier properties were achieved, whereas the grease barrier was moderate. Oxygen barrier property was improved when talc or cellulose was used as filler. The materials were also heat-sealable. However, some process scale-up issues (e.g. adhesion problems) remained unresolved. The xylan derivatives – in particular hydroxypropylated xylan (HPX) dispersions – could be coated as such, cross-linked, plasticized and filled with talc or nanoclay and showed good grease barrier properties in all cases. The barrier-enhancing fillers concept was demonstrated and WVTR of 46 g/(m2_d) and OTR of 72 cc/(m2_{d bar) were achieved.} In addition, the concept of low DS combined with external plasticization, enabling a bio content of up to 90%, was tested successfully. The colour of the coating material colour was white and remained stable during drying and converting. Heat sealability was achieved, and

Figure 2. Pilot trial equipment at VTT.

PE extrusion coating was possible leading to OTR values below 10 cc/(m2_{d bar). Die-cutting} and press-forming into trays was successful. In conclusion, several potential barrier dispersion coatings were developed and demonstrated

and multi-layer paperboard structures with several beneficial characteristics, especially grease barrier properties, were produced. All of the derivatives require further optimization according to the target end use, but can be readily utilized at the industrial scale.

Figure 3. Best barrier properties of the three most promising derivatives normalized at 20 µm thicknesses,

measured at 23 o_{C, 50%RH. The targeted area in Figure a) is in the top left corner and in Figure b) in the}

bottom left corner.

Improving grease resistance of starch-based coatings

When synthetic polymer was added to modified starch-based dispersion (dual- polymer system) at optimized amounts, efficient grease resistance was achieved. The addition of synthetic polymer to starch-based coatings improved the elastic properties and plasticity and, subsequently, the mechanical convertability of the product. Addition of plate- like like pigment to the renewable dispersion coating increased the grease resistance of the non-converted blanks, whereas micro- scale cracks in the barrier were frequently observed after tray conversion, resulting in poor grease resistance.

Effect of hemicellulose removal on convertability

The effect of fibre composition on convertability was studied by preparing a novel papermaking fibre with cellulose-rich fibre surfaces by enzymatic hemicellulose removal. Xylanase treatment of refined never- dried bleached birch kraft pulp demonstrated selective hydrolysis of xylan from the outermost fibre layers, reducing 14.2 wt% of the total amount of xylan in the studied pulp. The mechanical properties of paperboard at 180 g/m2 _{grammage were mainly preserved} despite a 14.2 wt% reduction in xylan content. Press-forming of the produced materials revealed differences related to the end moisture content of the produced paperboard (i.e. drying severity), fibre composition (i.e. hemicellulose content), and press-forming parameters. Consequently, the suitability of the paperboard could be optimized for flexible packaging by tailoring the carbohydrate composition of the base substrate.

4.2 Improving formability of paper-based