Compatibilizing Degradable Polymer Blends for Recycling Applications Using Nanocellulose

Mixed sorting of plastics at recycling facilities limits the capacity for recycling, because many synthetic organic compounds are incompatible with others at the molecular level, resulting in high interfacial tensions and immiscible blends. Consequently, less than 9% of United States plastic is recycled annually.¹ While research has displayed blend enhancement by organoclays, phyllosilicates functionalized with organic molecules, and silica-coated cellulose nanofibers (sCNF) and microfibers (sCMF), phase separation in nanocomposites still poses extensive limitations for recycling competence.² Thus, this study aims to understand the mechanical and interfacial impact of adding organoclay, clay combined with resorcinol bis(diphenyl phosphate) (RDP), which is a flame retardant, sCMF, and sCNF to commonly recycled nanocomposite blends, exploring potential solutions to polymer incompatibility. We hypothesized that organoclay application would decrease interfacial tension while sCNF and sCMF treatment would enhance mechanical strength and flame retardance.<br/>50-gram blends of 35 g polylactic acid (PLA) and 15 g polystyrene (PS) were composited with various copolymers (e.g., C-20A, C-30B, acryl-sCMF, sCMF, RDP-clay) at various concentrations (1%, 3%, 5%) in a Brabender at 180°C for 10 minutes and molded into necessary formats for experimentation (rectangular prisms, dogbones, notched for impact strength testing). Differential scanning calorimetry was initially conducted on the control, C-20A, and C-30B samples, revealing slight convergence in polymer glass transition (T_g) temperature: C-20A induced a -0.41°C alteration in Tg difference between PLA and PS compared to the control while the C-30B displayed a -1.13°C change, two statistically-insignificant modifications. Dynamic mechanical analysis revealed that C-30B also boosted amalgam elasticity. Transmission electron microscope (TEM) imaging qualified these results, however, because C-20A was found at the PLA-PS interfaces more than C-30B, which was commonly in the PLA domain. Sample impact strength findings demonstrated that clay increased composite brittleness, while sCMF and sCNF affected impact strength insignificantly within error. Tensile testing imitated these conclusions: Incorporating 3% acryl-sCNF in the PLA:PS resulted in ultimate tensile strength of 37.16 MPa and Young’s modulus of 1.37 MPa compared to 37.96 MPa and 1.33 MPa for the control sample. Similarly, including 3% acryl-sCMF in PLA:PS blends insignificantly altered tensile results.<br/>Similar compounding of 35 g PLA and 15 g polycaprolactone (PCL) occurred next, and impact strength testing revealed the PCL sample’s superiority in this category. The inclusion of cellulose nanotubes (sCNF) in PLA:PCL blends consistently increased blend impact strength. However, we found that the incorporation of 5% sCNF into the PLA:PCL blends improved impact strength most significantly (+95.5 ± 15.13 (J/m)). Tensile testing also displayed PCL’s augmentation of PLA ductility<br/>In order to understand the improved performance of 5% sCNF PLA:PCL blends, further studies are planned of the interfacial structures between the different nanocomposites, using TEM on thin cryo-microtome sections, as well as contact angle measurements to correlate the results to the force of adhesion and its modification using the different nanoparticles. Finally, the impact of flame retardance on the blends will be measured using the UL-94 testing protocols.<br/>We would like to thank the Louis Morin Charitable Trust for supporting this research. We also gratefully acknowlege Professor Young-Soo Seo and Sejong University, South Korea, for providing the CelluloSys utilized during this study.<br/><br/>1Bourtsalas, Yepes, I. M., & Tian, Y. (2023). Journal of Environmental Management, 344, 118604. https://doi.org/10.1016/j.jenvman.2023.118604<br/>2Dorigato, A. (2021). Advanced Industrial and Engineering Polymer Research, 4(2), 53–69. https://doi.org/10.1016/j.aiepr.2021.02.00