Table 4 PLC criteria and their relevance for 3D printing materials
PLC criterion | Specification according toa | Classification of the tested polymers |
|---|---|---|
No reactive functional groups | amino groups, epoxide groups, unsubstituted positions ortho- to phenolic hydroxyl (ecotoxicological concern only for amino groups) | The molecular structure of polymers used in 3D printing powders do not include any of these groups. The measured reactivity is very low |
Molar mass | Molecular weight above 10.000 g/mol | Product specification of the thermo-plastics typically used for 3D printing |
Extractivity in water | 10 mg/L is seen as acceptable | Such test was not performed in the present project. |
Metal content | No fixed limit is given by the OECD concept | The analysis of the polymer powders by XRF confirmed metal content below 0.1%, containing metals such as Al Si P K Fe. One material had Al Si K up to 1%, most probably from cryo-milling. |
Cationic charge density | not more than one cationic charge in 5000 monomer units (EPA definition) | The molecular structure of PA and PU does not contain cationic groups |
Stability | Stable under the conditions of use | PU materials are stable under aquatic conditions, as intended. PUs are susceptible to partial biodegradation during the harsher conditions of industrial composting [14]. Consideration of degradation products from marine conditions is challenging via identification and toxicity prediction [56]. |
Swelling | 100% water uptake | Not relevant for 3D printing powders |