# Closed Circuit of 3-Dimensional Polymer Powders
## 3 Materials and Methods
### Material Readiness Models  
Mixing and seasoning of material in the form of powders applies to polyamide-nylon--more precisely: PA12, PA11 and PA6; and PA12 + aluminum addition. This is the material group most often used in this technology: powder with a globular morphology ranging in size from 20 to 100 \(\upmu\)m, with a dominant fraction of 60 \(\upmu\)m. The material is very loose.  
The input to the basic 3D printing process is the result of mixing three components, i.e., post-process material (UM), new (fresh) (NM) and recycled (ReM). Examples of mixture proportions are, for example UM/NM/ReM, e.g., 50/40/10. The grading system sifts through 200 micro sieves. Ultrasonic sieves (e.g., 20-40 kHz) can be used to speed up this process. The mixed material is seasoned for approximately 24 h. During this time, the humidity must be stabilized in the range of 40-60%.  
Fineness Check under Target Operating Conditions (IRL-7)  
Measurement using the Dynamic Image Analysis method (ISO 13322-2) [36] with a system of two cameras working simultaneously allows for the analysis, assessment and verification of the polymer powder and the measurement of a wide range of geometric features, and the results obtained are repeatable and characterized by a resolution many times higher than the measurement results that are possible to be obtained by sieving.  
Figure 7: View of the RPW razor blade mill control panel: mill, feeder, opening and closing valves; with illustrations of these devices; analogue and digital meters; selected parameters of processing machines and equipment.  
The purpose of granulometric analysis of polymer powder is to find out the particle size distribution in the obtained sample (Figures 8-10). The polymer particles are too small and the material is naturally susceptible to electrostatic phenomena, so the traditional and popular analytical method of sieve analysis cannot be used here. The dynamic image analysis method was used (Method: Analyses of the form and geometric dimensions of polymer particles, ISO 13322-2) [36]. Device: CAMSIZER X2 (Microtrac Retsch GmbH, Haan, Germany), dry dispersion in an air stream (X-Jet). Material type: polymer in powder form. Sample quantity: approx. 5 mL per one measurement.  
TEST 1: Repeatability test: The test involved taking two measurements of the same material and then comparing the results to determine whether the tested measurement method and the device itself provide repeatable results.  
Measurement 1: Two samples with a volume of approximately 5 mL (2 teaspoons) taken from the same batch of material were measured successively.  
Summary and conclusions:  
1. The first look (Figure 9) allowed us to conclude that the same material was measured (and it was NM and ReM), and the measurement itself was highly repeatable.
2. A maximum difference of just over 0.4% appeared on the flattened curves, i.e., for the range of particles whose percentage share in the total volume is large.  
Such a deviation is practically negligible, especially when you consider random sampling (spoon collection without the use of a sample splitter).  
TEST 2: Repeatability test continued. It is possible to present the measurement result in tabular form for freely defined classes (virtual sieves). Table 5 presents the results for ten linearly arranged sieves ranging from 0 to 100 \(\upmu\)m for both measurements, where p3 and Q3 are the percentages of dimension classes p3--real, Q3--cumulative.  
TEST 3: Repeatability test continued. Because the device can save photos of analyzed particles (all or according to a given criteria), it can look at individual particles in terms of various parameters and geometric features, e.g., size and shape.