Coatings 2023 , 13 , 195
2of 16
on DOW’s styrene-butadiene latices, for example, on DL 966 grade; however, such specific grade is no more available on the market. Moreover, previous studies focused on the addition of functional inorganic fillers, which are already widely used in the paper-based packaging industry [13–15,19–22] as a top coat to improve printability and glossiness or to improve moisture barrier properties of the coated substrates. On the contrary, recent academic studies focused their attention on biobased polymers and additives, such as polysaccharides, proteins, and fatty acids [22–27]. However, at present, such solutions are produced mostly at a laboratory scale, with some EU-granted projects trying to scale them up, for example, R3PACK (https://www.r3pack.eu/ (accessed on 1 December 2022)), CelluWiz (http://www.celluwiz.eu/ (accessed on 5 June 2022)), and Ecofunco (https://www.ecofunco.eu/ (accessed on 5 June 2022)). Current issues may be related to feedstock availability, extraction process, or its yield, as well as—generally— higher cost. Focusing on the readily available solutions for a large-scale application—that is, based on already-industrialized latices and fillers—this paper aims to formulate and test new experimental formulations involving styrene-butadiene latices filled with kaolin as a func- tional filler to improve barrier properties; at the same time, the authors benchmark such performance against current formulations available commercially. 2. Materials and Methods 2.1. Substrates In this work, two virgin kraft fiber substrates were considered: • Mondi Group (Weybridge, UK) ProVantage Komiwhite (125 g/m 2 ), a white top kraft liner (KB); • MetsäBoard (Espoo, Finland) MetsäBoard Pro WKL (145 g/m 2 ), a double-coated white top kraft liner (KP). Such paper grades are already used in paper- and corrugated-board-based packaging and represent solutions for both flexible packaging and rigid packaging, if processed as top liners for corrugated board. The main difference between the two papers is in the porosity of the side to be coated, that is, lower porosity for KP due to the double top coating. 2.2. Commercial Coatings and Experimental Coatings Formulation In order to compare performances with those of present commercial products, two commercial barrier-coating grades were considered in this work: • SB-B: styrene-butadiene dispersion coating with a dry solid content of 50% (on a weight basis); the formulation does not involve inorganic fillers. • SA-B: styrene acrylate dispersion coating with a dry solid content of 46% (on a weight basis); the formulation does not involve inorganic fillers. Both commercial coatings were used as provided. Stirring with a magnetic anchor at 500 rpm occurred for 30 min before the coating application. Fourier-transform infrared spectroscopy (FTIR) analyses using a Thermo Scientific (Waltham, MA, USA) Nicolet iS 10, and differential scanning calorimetry and thermogravimetric analyses (DSC-TGA) using a TA Instruments (New Castle, DE, USA) SDT Q600 are reported in Appendix A. Regarding the experimental formulation, two styrene-butadiene latices were kindly provided by Trinseo (Horgen, Switzerland): • HPH 39: styrene-butadiene latex, T g ∼ = 0 ◦ C, dry solid content 54%. • HPH 40: styrene-butadiene latex, T g ∼ = 15 ◦ C, dry solid content 53%. This grade is reported by Trinseo to be similar to DL 966, the grade widely reported in previous literature [14,15]. Kaolin was used as a filler in experimental formulations. The specific grade was Cam- Coat 80 from Amberger Kaolinwerke (Hirschau, Germany), provided as pellets. Particle distribution is reported in Table 1. EXOlat C40 sodium polyacrylate, kindly provided by
Made with FlippingBook - professional solution for displaying marketing and sales documents online