# Closed Circuit of 3-Dimensional Polymer Powders
## 2 Literature Review, Introduction  
Popular additive manufacturing technologies are assigned to specific groups and dominant processing phenomena [4; 26; 27]: FDM--Fused Deposition Modeling melted material; RC--Robocasting; MJS--Multiphase Jet Solidification; SFF--Solid Freeform Fabrication; SLA--Stereolithography; DLP--Digital Lamp Processing; LAMP--Large Area Maskless Photopolymerization; ZPP--Two-Photon Polymerization; DOD--Drop On Demand; MJ--Material Jetting; NP--NanoParticle Jetting; BJ--Binder Jetting binders; SLS--Selective Laserintering; SLM--Selective Laser Melting; DMLS--Direct Metal Laser Sintering; EBM--Electron Beam Melting; MJF--Multi Jet Fusion; LENS--Laser Engineered Net Shaping; EBAM--Electron Beam Additive Manufacturing; DMT--Direct Metal Tooling; LOM--Laminated Object Manufacturing; and UC--Ultrasonic Consolidation.  
According to the study by the Production Engineering Committee of the Polish Academy of Sciences, Production Digitization Section [3], additive manufacturing methods are divided according to the type of bonding of materials, i.e., chemical bonds, sintering and gluing. Most often, they are referred to using abbreviations derived from their English names. The most popular methods are [3]: SLA (Stereolithography); FDM (Fused Deposition Modeling--shaping with plastic material); JM (English: Jet Modeling--stream modeling); 3 DP (3D Printing)--3D printing by combining powder with a binder; SLS (Selective Laser Sintering)--selective laser sintering of plastic and metal powders; and LOM (Laminated Object Manufacturing)--production of products by lamination.  
One of the standards defines the nomenclature that should be used in issues related to additive technologies, as well as the method of dividing these technologies in accordance with the current state of knowledge (ISO/ASTM 52900:2021 [28]). The standard specifies division technology molding additive on seven main groups: forming by spraying binder (binder jetting); forming with a directed energy deposition; material extrusion; material spraying (material jetting); powder fusion (powder bed fusion); lamination (sheet lamination); polymerization in a vat (vat polymerization).  
Based on a review of the current bibliography of the problem, it can be concluded that: firstly, different process efficiencies, product quality and non-toxicity of products and processes do not indicate the dangers of closed-loop engineering, but do indicate that there is an urgent need to develop and implement a new approach for recycling polymer powders for 3D additive manufacturing; secondly, there is a need for the creation of the structure of machines and devices for geometric stabilization of post-consumer powders; thirdly, there is a need for a systemic approach to the topic in terms of further development of a specific, intelligent system for regenerating polymer powders (RePTP) based on original techniques, ideas, and designs of machines and devices for their preparation (processing). Connections and structural changes between green and conventional energy markets supplying CO\({}_{2}\) emission cycles need to be clarified [29].  
A new method of recycling polyamide powders for reuse in the selective laser sintering process is a new idea, a new automated design of a machine installation [30], new process parameters and new configuration of the input powder composition for the additive manufacturing of technical elements. In addition to available technologies, home 3D printing devices using waste polymers are a new, potential solution with the highest possible degree of future implementation, e.g., compare [31; 32; 33].