Abstract
Polylactic acid (PLA) filaments are very popular as a thermoplastic source used in the 3D printing field by the “Fused Deposition Modeling” method in the last decade. The PLA market is expected to reach 5.2 billion US dollars in 2020 for all of its industrial uses. On the other hand, 3D printing is an expanding technology that has a large economic potential in many industries where PLA is one of the main choices as the source polymer due to its ease of printing, environmentally friendly nature, glossiness and multicolor appearance properties. In this review, we first reported the chemical structure, production methods, general properties, and present market of the PLA. Then, the chemical modification possibilities of PLA and its use in 3D printers, present drawbacks, and the surface modification methods of PLA polymers in many different fields were discussed. Specifically, the 3D printing method where the PLA filaments are used in the extrusion-based 3D printing technologies is reviewed in this article. Many methods have been proposed for the permanent surface modifications of the PLA where covalent attachments were formed such as alkaline surface hydrolysis, atom transfer polymerization, photografting by UV light, plasma treatment, and chemical reactions after plasma treatment. Some of these methods can be applied for surface modifications of PLA objects obtained by 3D printing for better performance in biomedical uses and other fields. Some recent publications reporting the surface modification of 3D printed PLA objects were also discussed.
Highlights
IntroductionPoly(lactic acid) is a biobased, biocompatible and biodegradable polymer which is generally produced from renewable sources (e.g., corn, sugar cane, wheat, and rice)
It is well-known that the use of Polylactic acid (PLA) filaments as the thermoplastic source in the Fused deposition modeling” (FDM) 3D printing practice has been expanding in the last decade since PLA polymer is one of the best choices as a source due to its ease of printing, environmentally friendly nature, glossiness and multicolor appearance properties
It was determined that many different methods have been proposed in the literature for the permanent surface modifications of PLA where covalent attachments were formed such as alkaline surface hydrolysis, atom transfer polymerization, photografting by UV light, plasma treatment, and chemical reactions after plasma treatment
Summary
Poly(lactic acid) is a biobased, biocompatible and biodegradable polymer which is generally produced from renewable sources (e.g., corn, sugar cane, wheat, and rice). The PLA polymer can be obtained by two different polymerization routes where the first one is the direct condensation of lactic acid using solvents under high vacuum and the second is the formation of the lactide which is a cyclic dimer intermediate where no solvent is used [8,9,10,11,12,13,14,15]. PLA is a relatively hydrophobic polymer with a static water contact angle in the range of 75–85◦ which results in a low cell affinity in biomedical applications and sometimes cause an inflammatory response from the surrounding tissue with direct contact [33,34] It has carbonyl and methyl groups as the pendant chemical groups on the backbone chain, PLA is somewhat a chemically inert polymer that lacks enough reactive side-chain groups, which prevents its easy surface and bulk modifications. These well-established additives are antioxidants, heat stabilizers, light stabilizers, impact modifiers and several others [10]
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