Effect of filler additions on pilot-scale extrusion coating of paperboard with PLA-based blends

Abstract

We study the incorporation of minerals (talc, kaolin and surface-treated calcium carbonate) in paperboard coatings based on PLA to improve their performance, often limited by the low crystallinity and moderate gas barrier of the polymer. Masterbatches of PLA-based blends mixed with the mineral fillers were melt-blended in a twin-screw extruder and applied as a coating on paperboard in a pilot-scale unit operating at velocities up to 140 m/min. Thermal imaging was used during the extrusion coating and the effect of the fillers was investigated as far as processability and their effect on the mechanical performance. A reduction of neck-in and improved adhesion between the coating and the substrate were achieved at intermediate mineral loadings. Excess filler and low coating weight generated pinholes, leading to a reduction of the integrity and mechanical properties of the coatings. Overall, we define the performance window for continuous, pilot-scale coating of paperboard with a biopolyester filled with mineral particles, opening the opportunity to realize operations in industrial settings.

Mineral-filled biopolyester coatings for paperboard packaging materials: barrier, sealability, convertability and biodegradability properties

“…Compounding and extrusion coating has been executed as described in our previous study (Helanto et al 2022). Masterbatches of 70 wt% of matrix polymer and 30 wt% of mineral filler were melt compounded with twin-screw extruder (counter-rotating 25 mm Coperion ZSK 26 Mc, 32 L/D ratio with K-Tron gravimetric side feeder K-ML-KT20, 200 rpm).…”

“…The hydrophobicity of the fillers plays also a role (Yu et al 2012) as being part of a material against water vapor. As the fillers have also had negative impact on the barrier results, those could be explained by minor defects (Helanto et al 2022) or by filler level that has not been optimal working as compatibilizer in the PLA based blend. For example, similarly increased WVTR were observed with the same Mater-Bi polymer and 3 wt% of talc compared to the 1 wt% and 4 wt% additions in our earlier study (Helanto et al 2021b).…”

“…Nevertheless, one of the key drivers for the packaging industry are the sustainability and regulatory aspects (Cameron 2020), and alternative barrier coating materials have been widely researched (Helanto et al 2019). PLA, has offered a bio-based and biodegradable alternative for paper and paperboard barrier coatings (Lahtinen et al 2011, Lahtinen et al 2012, Cheng et al 2015, Khajeheian et al 2016, Koppolu et al 2019, Sundar et al 2020, Helanto et al 2022). PLA has disadvantages e. g. its poor thermal and gas resistance and brittleness (Sonjui and Jiratumnukul 2014, Zou et al 2015, Khuenkeao et al 2016, Phetwarotai and Aht-Ong 2016, Amirabadi et al 2018, which have been enhanced e. g. by blending with flexible polymers, plasticizers or fillers (Zou et al 2015, Khuenkeao et al 2016, Phetwarotai and Aht-Ong 2016.…”

“…Mineral fillers such as platy talc (Mg 3 Si 4 O 10 (OH) 2 ) (Courgneau et al 2012, Jain et al 2012, Ouchiar et al 2015, Buzarovska et al 2016, Ouchiar et al 2016, Ghassemi et al 2017, Amirabadi et al 2018, Lee et al 2020, Helanto et al 2021a, Helanto et al 2021b, Helanto et al 2022, platy kaolin (composed mainly of kaolinite (Al 2 Si 2 O 5 (OH) 4 )) (Matusik et al 2011, Ouchiar et al 2015, Segura González et al 2015, Ouchiar et al 2016, Helanto et al 2021a, Helanto et al 2022, and more irregularly shaped calcium carbonate (CaCO 3 ) (Sabzi et al 2012, Piekarska et al 2017, Rocha et al 2018, Aliotta et al 2019, Helanto et al 2021a, Helanto et al 2022) have been combined with PLA matrix to improve its properties. Fillers have multiple ways of enhancing the barrier properties.…”

“…In addition, fillers have also been seen beneficial promoting compatibility of immiscible polymer blends (Jain et al 2010, Helanto et al 2021b or increased the hydrophobicity of the matrix (Yu et al 2012), and therefore having a positive effect on the barrier properties. Negative effects of filler additions in barrier point of view are naturally e. g. unfavorable filler orientation (Evstatiev et al 2013), pinhole generation and agglomerates (Massey 2003, Helanto et al 2022.…”