Citation: Nejström, M.; Andreasson, B.; Sjölund, J.; Eivazi, A.; Svanedal, I.; Edlund, H.; Norgren, M. On Structural and Molecular Order in Cellulose Acetate Butyrate Films. Polymers 2023, 15, 2205. https:// doi.org/10.3390/polym15092205 Academic Editors: Jungmok You, Jeonghun Kim and Carmelo Corsaro Received: 3 January 2023 Revised: 4 April 2023 Accepted: 15 April 2023 Published: 6 May 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article On Structural and Molecular Order in Cellulose Acetate Butyrate Films Malin Nejström 1,2 , Bo Andreasson 2 , Johanna Sjölund 3 , Alireza Eivazi 1 , Ida Svanedal 1 , Håkan Edlund 1 and Magnus Norgren 1, * 1 FSCN, Surface and Colloid Engineering, Mid Sweden University, 85170 Sundsvall, Sweden 2 Nouryon, 85467 Sundsvall, Sweden 3 FibRe-Centre for Lignocellulose-Based Thermoplastics, Fibre and Polymer Technology, KTH Royal Institute of Technology, 10044 Stockholm, Sweden * Correspondence: magnus.norgren@miun.se Abstract: Cellulose acetate butyrate (CAB) is a possible candidate, being a raw material derived from renewable resources, to replace fossil-based materials. This is due to its thermoplastic properties and the relative ease with which it could be implemented within the existing industry. With a significant amount of variation in CAB on the market today, a knowledge gap has been identified regarding the understanding of the polymer structural arrangement in films. This relates to the underlying mechanisms that regulate CAB film material properties, insights that are important in product development. In this study, commercially available CAB was investigated with XRD, SEM, AFM, and TOPEM DSC in order to obtain physicochemical information related to its micro-structural features in solvent-cast films. The film-forming ability relates mostly to the number of hydroxyl groups, and the semi-crystallinity of the films depends on the type and position of the side groups along the cellulose backbone. The appearance of signs of possible cholesteric ordering in the films could be connected to higher amounts of hydroxyl groups along the backbone that disturb the helix arrangement, while the overall order was primarily related to the butyrate substitution and secondarily related to the molecular weight of the particular CAB studied. Cold crystallization was also observed in one CAB sample. Keywords: cellulose acetate butyrate; cholesteric ordering; TOPEM DSC; crystallinity; film; commercial 1. Introduction Biobased plastic, originating from cellulose raw materials, is identified by the Eu- ropean Commission as a possible solution to replace oil-based plastics. Materials with properties similar to those of traditional plastics, but with a lower carbon footprint, are urgently needed [1]. Being an abundant, naturally occurring polymer with interesting prop- erties [2], cellulose constitutes a promising source for the development of more sustainable thermoplastic materials. Unfortunately, in the native form of cellulose, some important physicochemical properties of plastics are absent—for example, the glass transition state, T g , is so high that it is of no practical use [3]. Therefore, cellulose as a raw material can- not provide the fast-paced change that is needed. On the other hand, several cellulose derivatives exhibit T g at reasonable temperatures and could be useful as replacements for oil-based plastics [4–6]. Cellulose acetate butyrate (CAB) is a cellulose ester, where the hydroxyl groups at- tached to the glycoside rings in cellulose are substituted, partially or fully, by acetyl and butyryl groups [7]. The ratio between acetyl and butyryl substitution can be varied in their synthesis, and somewhat different properties can be obtained [8]. The total degree of substitution (DS) is regarded as a maximum of three; however, for a degree of poly- merization (DP) of less than 134, a slightly higher DS can occur due to the end-group Polymers 2023, 15, 2205. https://doi.org/10.3390/polym15092205 https://www.mdpi.com/journal/polymers