Promotion of molecular diffusion and/or crystallization in fused deposition modeled poly(lactide) welds

• Published in: Polymer (Guilford) 2020-08, Vol.202, p.122637, Article 122637
• Main Authors: Srinivas, Varun, van Hooy-Corstjens, Catharina S.J., Rastogi, Sanjay, Harings, Jules A.W.
• Format: Article
• Language: English
• Subjects: Additives; Calorimetry; Composition; Crystallization; Crystals; Diffusion; Diffusion rate; Fused deposition; Fused deposition modeling (FDM); Interfaces; Interlayers; Low molecular weights; Mechanical properties; Molecular diffusion; Molecular structure; Molecular weight; Nucleation; PLA additives; Plasticization; Polymer blends; Polymers; Rheological properties; Rheology; Stiffening; Stiffness; Weld interface; Welded joints; Welding
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2020.122637

Fused deposition modeled parts of polymeric origin exhibit inferior interlayer mechanical properties. To enhance interfacial weld stiffness, poly(lactide) blends containing low molecular weight polymers of chemically identical but enantiomerically different nature are explored. The enantiomeric composition of the low molecular weight fraction is either random or opposite, promoting molecular diffusion or nucleation respectively. The structure-relationship of the interfaces is studied using torsional stiffness, calorimetry, and rheology. Fully miscible, non-crystallizable low molecular weight additives of random L and D enantiomeric composition reduce melt viscosity and crystallization rate, promoting molecular diffusion. Nevertheless, incomplete entangling and crystallization upon interfacial mixing induce poor interfacial stiffening. Poly(lactide) stereocomplex enriched interfaces promote crystallization. Chains across weld interfaces may be mechanically anchored in crystals, but hindered diffusion limits molecular mixing and thus the extent of mechanical stiffening. Ultimately, combining melt plasticization and increased crystallization rates distinctly increases weld stiffness and thermodynamic/geometrical stability of fused deposition modeled poly(lactides). [Display omitted] •Selective enantiomeric design of bi- and multimodal PLAs stiffens FDM interfaces.•Random poly(DL-lactide) low molar mass additives promote interfacial diffusion.•Low molar mass stereocomplex enriched blends enhances crystallization in FDM .•PDLLA plasticization with stereocomplex nucleation stiffen FDM interfaces.