Architecture of covalent bonds between filament layers to enhance performance of 3D printing biodegradable polymer blends. (February 2022) - Lyu, Yang
Abstract: Generally, the filament layer adhesion in articles 3D printed by Fused Deposition Modeling (FDM, one of 3D printing method) is completely provided by the diffusion and entanglement of molecular chains between adjacent layers. However, the poor layer adhesion and strong anisotropy in FDM due to the difficult movement of polymer chains and the complex thermal history during 3D printing have turned to be the main factors restricting the development of FDM. In this paper, poly (lactic acid)/poly (butylene adipate terephthalate)/poly (lactic acid) grafted glycidyl methacrylate biodegradable blend (PLA/PBAT/PLA-g-GMA, PLA-g-GMA was a self-made compatibilizer) was used as the matrix. A low molecular weight three-armed PLA (noted as U-PLA) was synthesized by ring opening polymerization of lactide which was initiated by trimethylolpropane (TMP) and end capping with double bonds. Then, U-PLA and phenylbis (2, 4, 6-trimethylbenzoyl) phosphine oxide (XBPO) was added in the matrix. The rheological results found that U-PLA acted as a low molecular weight plasticizer to promote the fluidity of the matrix during 3D printing process. On the other hand, compared with polymer chains in matrix, U-PLA was more prone to cross interlayer motion, resulting in stronger physical entanglements. With UV irradiation, XBPO was triggered to release free radicals and initiated crosslinking at terminal double bonds of U-PLA which rich concentrated between adjacent layers. Molecular dynamics and experimental results showed that with increase of U-PLA, the interlayer bonding strength of FDM specimens increased significantly. The maximum tensile strength of 3D printing specimens increased by 82.5% (printing direction at 90°). This work clearly showed that with UV irradiation covalent bonds were successfully architected between filament layers of FDM specimens. Highlights: A three-armed PLA (capping with double bonds) was synthesized and exploited to construct chemical bonds between interlayer adhesion during 3D printing. With UV irradiation, the maximum tensile strength of 3D printing specimens increased by 82.5% (3D printing direction at 90°). The specimens were almost isotropic. The mesoscopic DPD model was established to further prove the feasibility of constructing covalent bonds between layers during 3D printing process.