Preparation of polyamide 12 powder for additive manufacturing applications via thermally induced phase separation

Dandan Su; Jingkui Yang; Shan Liu; Lulu Ren; Shuhao Qin

doi:10.1515/epoly-2022-0050

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Preparation of polyamide 12 powder for additive manufacturing applications via thermally induced phase separation

Dandan Su , Jingkui Yang , Shan Liu , Lulu Ren und Shuhao Qin

Veröffentlicht/Copyright: 9. Juni 2022

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Abstract

Spherical polyamide 12 (PA12) powder for selective laser sintering (SLS) was prepared by thermally induced phase separation (TIPS) method. It was authenticated that the mixed solvent can regulate the liquid–liquid phase separation (LLPS) process by changing the ratio of diluent to non-diluent. The polymer droplets mainly coalesced in the solution, and then the crystal nucleus of PA12 was formed in the droplets. Finally, high crystallinity PA12 powder was precipitated. The morphology, particle size distribution, thermal properties, the change of crystal structure, and powder spreading performances of the obtained powder were characterized. The powder had a narrow particle size distribution, an average particle size of 55.2 μm, and a broad sintering window of 29°C. The results exhibited that the powders prepared by TIPS had excellent sintering properties, and TIPS method provided more choices for SLS technology.

Keywords: polyamide 12; selective laser sintering; thermally induced phase separation; cloud point; polymer powder

1 Introduction

Additive manufacturing (AM), known as a technology for manufacturing parts with complex shapes in a molding cycle with high production efficiency, is applied to a variety of materials, such as metals and polymers (1,2). Selective laser sintering (SLS) is one of the most extensively used technologies to fabricate mechanical parts of various shapes layer-by-layer by melting and sintering polymer powder. Compared with other AM technologies, SLS can reduce cost and improve production efficiency (3–7). In the SLS process, the particle size of the powder material is mainly distributed in the range of 10–100 μm (8,9). Among them, the average particle size distribution of commercial powder is 50–70 μm.

In SLS technology, polyamide 12 (PA12) is a commercially widely used material (10,11), which has excellent comprehensive properties, good thermal stability, low melt viscosity, and low water absorption rate (12). The preparation methods of polyamide-based powder are mainly in the following three ways: emulsion polymerization (13,14), mechanical crushing (15,16), and solvent precipitation (17). Commercial PA12 powdered potato forms currently were prepared by solvent precipitation. At present, ethanol is often used as the solvent for the preparation of PA12 powder by solvent precipitation method (17,18), and the conditions of high temperature and high pressure are required. However, the choice of solvent and non-solvent is a difficulty that restricts the application of solvent precipitation. Mechanical crushing is a physical method to prepare the powder with narrow particle size distribution. The rough surface and irregular shape of the prepared powder bring poor fluidity during the laser sintering process. Monomers and emulsifiers are often used as raw materials for emulsion polymerization. After complete aggregation, cumbersome post-processing steps are required. The production cost of emulsion polymerization is high and the residue in the product is difficult to remove. Therefore, a new and efficient method for preparing PA12 powder is urgently needed.

Thermally induced phase separation (TIPS) method is one of the main methods for preparing membranes (19), which is driven by thermal energy in the phase transition process. In recent years, TIPS method is applied to the preparation of laser sintered powder. TIPS is non-mechanical, rapid, and efficient compared to other powder preparation methods (20).

Fang et al. (21) successfully prepared spherical polypropylene (PP) powder via TIPS using xylene as solvent. The particle size distribution of obtained PP powder was narrow, and the suitable particle size was 42.7 μm. The products obtained by laser sintering had good morphology and dimensional accuracy. Dechet et al. (22,23) used acetophenone as solvent to produce polyformaldehyde (POM) powder. POM powder with good fluidity was suitable for powder bed fusion even without any fluidity enhancer. Polybutylene terephthalate (PBT) powder was appropriated for laser beam sintering powder bed which was prepared by liquid–liquid phase separation (LLPS) and precipitation. The solvent cyclopentanone was determined by the screening method of solubility parameters. PBT powder with high crystallinity, narrow particle size distribution, and average particle size of 36 μm were obtained by phase separation. Zhu et al. (24) successfully prepared polyetherimide (PEI) nanoparticles ranging from 200 nm to 1 μm with dimethyl sulfoxide solution. Then, Zhu et al. (25) also prepared PEI nanoparticles by TIPS method and studied the effect of droplet evaporation on the nanoparticles. It was found that droplet evaporation and TIPS process were carried out simultaneously, which was helpful to prepare polymer nanoparticles with small and uniform particle size. So far, the TIPS method for the preparation of polymer powder mostly uses a single solvent. The regulation range and degree of single diluent on the system are limited. The use of mixed diluent not only expands the selection range of diluent but also adjusts the interaction between polymer and diluent by changing the ratio of the mixed diluent.

In this study, spherical PA12 powder was prepared by TIPS with N,N-dimethylacetamide (DMAC) and polyethylene glycol 400 (PEG400) as mixed diluent. The advantage of preparing nylon powder by TIPS was that the preparation process of PA12 powder was affected by changing the interaction between solvent and polymer. DMAC is a widely used polar solvent. PEG400 is a solvent employed for the preparation of PA12 membrane. The implementability of DMAC and PEG400 was determined by Hansen solubility parameters. The interaction between polymer and solvents was affected by regulating the proportion of mixed solvent. In the process of preparing PA12 powder with different morphology and particle size distribution by LLPS, the ratio of solvent affected the nucleation and growth time.

2 Mechanism of TIPS

The simplified phase diagram is depicted in Figure 1. The polymer dissolves in the solvent at high temperature and becomes homogeneous. With the decrease of temperature, the system enters the unstable stage through the binodal line, and LLPS occurs. The system reverts to plateau via debasing free energy. The metastable region is located between the binodal line (solid line) and the spinodal line (dotted line). When the polymer concentration is lower than the critical point, LLPS occurs in the metastable region on the left side and the poor polymer phase droplets disperse in the rich diluent phase. On the right side of the critical point, the polymer concentration is relatively high, and the poor diluent phase disperses in the rich polymer phase (26,27). In the metastable region, the growth of polymer droplets is based on mechanization of coalescing or Ostwald ripening. The polymer crystal nucleus is formed in the droplet, the crystals grow until they are precipitated from the solvent, and the solution becomes an emulsion (28). The particle size of the powder depends on the droplets. At a constant cooling rate, there is enough time for the growth of powder particles with the expansion of the metastable phase region (29,30). In this study, the phase separation is determined to locate on the left side of the critical point owing to the lower concentration of PA12. The metastable region is altered by changing the solvent ratio to control the particle size of PA12 powder.

Figure 1

Phase diagram of binary polymer–solvent systems (39–41).

3 Materials and methods

3.1 Materials

Raw material PA12 pellets (Evonik Industries AG). DMAC was purchased from BASF, Germany. PEG400 was provided by Jiangsu Hai’an Petrochemical Co. Ltd. (China).

3.2 Experimental

3.2.1 Preparation of PA12 powder

The whole process of preparing PA12 powder by TIPS is shown in Figure 2. The proportions of experimental samples are shown in Table 1. PA12 pellets and mixed solvents were added in a three-port flask in proportion. The mixture was heated with stirring at 160°C for 30 min until the polymer was completely dissolved, then the solution was cooled to 120°C and maintained for 2 h. The stirring speed was 380 rpm and the whole process was stirred at this speed. The TIPS process began with the decrease of temperature, LLPS occurred in PA12/DMAC/PEG400 system, and PA12 rich phase droplets appeared. With the continuous decrease of temperature, polymer droplets coalesced, and small droplets became larger droplets. When the temperature was further reduced below the crystallization temperature, PA12 nucleated homogeneously in the system, and finally solidified and precipitated. At this point, the TIPS process ended. After that the solution was cooled to ambient temperature, the primary powder was completely washed with pure water many times, and then filtered and dried at 60°C for 12 h.

Figure 2

Schematic diagram of the preparation of PA12 powder (39).

Table 1

Sample number and composition of the experiment

Sample	PA12 (wt%)	DMAC (wt%)	PEG400 (wt%)
I	5	65	30
II	5	70	25
III	5	75	20
IV	5	80	15
V	5	85	10

3.2.2 Measurement of cloud point and crystallization temperature

The cloud point is at the beginning of phase separation of the system. Therefore, the cloud point temperature (T _cloud) plays an important role in detecting the phase separation behavior. In this experiment, the T _cloud and crystallization temperature (T _c) of different solvent ratio systems were observed by changing the content of DMAC. The measurement process of T _cloud and T _c was as follows: take a small piece of polymer diluent mixture sample and place it between two glass slides, heat the system to 190°C and keep it for 10 min to completely dissolve it. Gradually cool down at the rate of 1.5–2°C·min⁻¹, when the droplets appear, the temperature is recorded as T _cloud, then the temperature at which the crystal appears is recorded as T _c.

3.3 Characterization

3.3.1 Scanning electron microscope (SEM)

Powder morphology was observed by field emission scanning electron microscope (FE-SEM, FEI Quanta Feg250, USA). The powders were treated with gold spraying in advance.

3.3.2 Particle size distribution

For all samples, the particle size distribution was measured using a Bettersize 2600 laser particle size analyzer (wet), which used laser diffraction to determine the particle size distribution of powders suspending in water. The span was calculated according to the following equation:

(1) Span = χ 90 , 3 − χ 10 , 3 χ 50 , 3

where χ _90.3, χ _50.3, and χ _10.3 are the total volume distribution Q₃ below 90%, 50%, and 10%, respectively.

3.3.3 X-ray diffraction (XRD)

XRD spectra of PA12 pellets and powder were collected in the 2θ range of 5–60° using an X-pert PRO diffractometer (Philips, The Netherlands) with a copper Kα X-ray source.

3.3.4 Fourier transform infrared spectroscopy (FTIR)

The solvent effect on the molecular structure of polymers prepared via TIPS was determined using FTIR (Thermo Nicolet 6700, USA). PA12 pellets were tested as a reference material. The spectrometers of FTIR were recorded from 4,000 to 400 cm⁻¹, with a scanning frequency of 4 cm⁻¹.

3.3.5 Differential scanning calorimetry (DSC)

The melting and crystallization behavior of PA12 powder and pellets in nitrogen phenomenon were studied by DSC (Q20, TA instrument), and all samples were heated and cooled at a rate of 10°C·min⁻¹ in the temperature range of 40–220°C. The crystallinity χ _C of these samples can be calculated by the following equation:

(2) χ C = Δ H m Δ H m 0 × 100 %

where ΔH _m is the enthalpy of melting of the PA12 powder and PA12 pellets. Δ H m 0 = 209.3 J·g⁻¹, which is the theoretical melting enthalpy of 100% crystalline PA12 (31).

3.3.6 Bulk density

The test process of bulk density is to place the powder into the 100 mL receiver through the funnel, and scrape the sample along with the mouth of receiver with a ruler. The device of bulk density is shown in Figure 3. The weight of the receiver is accurately weighed before and after loading, and the bulk density can be calculated according to the following equation:

(3) ρ = W − W 0 V

where W is the weight of the receiver with a specimen, W ₀ is the weight of the receiver, and V is the volume of the receiver, 100 mL. Take the average of the results of five measurements.

Figure 3

Device for setting bulk density.

3.3.7 Angle of repose (AOR)

AOR is used for indicating the flowability of the material. The funnel is placed vertically. The powder is transferred to the funnel at an angle until the top of the powder pile reach the bottom of the funnel. The test process of AOR is shown in Figure 4. The angle between the powder pile slope and the horizontal plane is defined as AOR, which is calculated as follows:

(4) AOR = arctan H R

where H is the height of the conical pile and R is the average radius of the powder pile measured from five different positions.

Figure 4

Device for setting AOR.

4 Results

4.1 Determination of solvent

The compatibility of solvent and polymer is judged by the Hansen solubility parameters (32). The parameters of the dispersion forces δ _d, the polar interactions δ _p, the hydrogen bonding interactions δ _h, the total Hansen solubility parameters δ _t, and the difference in total Hansen solubility parameters Δδ _t between PA12 and solvent are summarized in Table 2. The total Hansen solubility parameters δ _t (33) can be calculated by the following equation:

(5) δ t 2 = δ d 2 + δ P 2 + δ h 2

Table 2

Hansen solubility parameters of PA12 and solvents (32)

Polymer/solvent	δ _d (MPa^1/2)	δ _p (MPa^1/2)	δ _h (MPa^1/2)	δ _t (MPa^1/2)	Δδ _t (MPa^1/2)
PA12	18.5	8.1	9.1	22.2	—
DMAC	16.8	11.5	10.2	22.7	0.5
PEG400	16.6	3.7	13.3	21.6	0.6

The parameter Δδ _t between PA12 and DMAC is 0.5 MPa^1/2 and the parameter Δδ _t between PA12 and PEG400 is 0.6 MPa^1/2. Smaller parameter Δδ _t indicates good compatibility. Polar polymers and solvents have good compatibility, which not only meet the principle of “similar compatibility,” but also “similar polarity.” The similar parameters of PA12 and solvents satisfy the principle of “similar solubility.” The values of δ _d and δ _h have little difference. The parameters δ _p of PA12 and DMAC are 8.1 MPa^1/2 and 11.5 MPa^1/2, while PEG400 is only 3.7 MPa^1/2, which shows that the polarity of PEG400 and PA12 is quite different. The increase of PEG400 content will reduce the polarity of the system and debase the compatibility between PA12 and solvents. Therefore, DMAC was selected as the good solvent and PEG400 as the poor solvent to form the mixed solvents to dissolve PA12 pellets. PA12 powders with different particle sizes were precipitated by regulating the proportion of DMAC and PEG400.

4.2 Preparation of PA12 powder for SLS with PA12/DMAC/PEG400 system

4.2.1 Cloud point curve of PA12/DMAC/PEG400 system

To gain more insight into the phase separation process of polymer–solvent system, the cloud point of components with different ratios during heating and cooling can be tracked by hot stage optical microscope.

The binary phase diagram is drawn from the data observed by the hot stage microscope. The content of DMAC changed from 65 to 85 wt%, and the T _cloud and T _c of PA12/DMAC/PEG400 system are recorded in Figure 5. It should be noted that TIPS usually needs a dissolution temperature above the melting point of the polymer. In this work, the solution temperature (160°C) was lower than the theoretical melting point (∼178°C) of PA12, which greatly reduced the energy consumption of powder preparation. In addition, it was found through the preliminary attempted experiments that when the content of PEG400 was higher than 35 wt%, PA12 pellets cannot be completely dissolved. Therefore, the content of PEG400 should be less than 35 wt%.

Figure 5

Phase diagram of PA12/DMAC/PEG400 samples and the phase separation image of Sample I.

The T _cloud is mainly influenced by polymer concentration and diluent ratio. In this work, the polymer concentration was defined at 5 wt%. From the phase separation image of Sample I, the phenomena of LLPS and crystallization can be obviously observed. The phase separation appearance of other samples was similar. The T _cloud decreased with the increase of DMAC content, while the T _c changed little. The higher the T _cloud, the more unstable the system was, and the LLPS process was prone to occur under lower external temperature or concentration perturbations. With the further decrease of temperature, the diluted phase and polymer phase continued to exchange materials, and the droplets gathered and grew until the polymer solidified.

4.2.2 Interaction between PA12 and DMAC/PEG400 mixed diluent

The part between T _cloud and T _c belongs to the LLPS region. The region decreased with the increase of DMAC content. The interaction between PA12 and solvents can be calculated via the interaction parameter χ (34) with the following equations:

(6) χ = V i RT ( δ i − δ j ) 2 + 0.34

(7) V i = V 1 ϕ 1 + V 2 ϕ 2

(8) δ i = δ 1 ϕ 1 + δ 2 ϕ 2

where R = 8.314 is the ideal gas constant, T = 298 K (25°C), and V _i is the molar volume of diluent, which can be calculated by the equation V _i = M _i/ρ _i. δ _t is the solubility parameter of the solvent and δ _j is the solubility parameter of the polymer. V ₁, ϕ ₁, δ ₁ are the molar volume, volume fraction, and solubility parameter of DMAC, respectively. V ₂, ϕ ₂, δ ₂ are the molar volume, volume fraction, and solubility parameter of PEG400, respectively.

The interaction between PA12 and mixed diluent played an important role in the LLPS process. When the interaction between polymer and diluent was poor, the T _cloud of the system occurred at a higher temperature. When the interaction was strong, solid–liquid (S–L) phase separation occurred along with LLPS. The interaction parameters are summarized in Figure 6. The smaller χ values indicated stronger interaction and better compatibility (35). Figure 6 shows that the χ values decrease with the increase of DMAC content, and the result indicated that the compatibility of PA12 and solvents increased continuously.

Figure 6

The interaction parameters of the image about the PA12/DMAC/PEG400 system changed with the content of DMAC.

4.2.3 Effect of solvent ratio on powder morphology and particle size distribution

The SEM images of the morphology and particle size distribution of PA12 powder are shown in Figure 7. SEM shows that the powders have irregular morphology, poor dispersion, and large particle size. With the increase of DMAC content, the morphology of the powder improved gradually. The powder of Sample III has spherical morphology, while the powder shapes of Samples IV and V were relatively sharp.

Figure 7

Morphology and particle size distribution of PA12 powder.

The average particle size of the powder decreased with the increase of DMAC content. The D50 were 443.80, 81.52, 55.20, 51.08, and 41.93 μm. With the increase of DMAC content, the particle size distribution diagram showed that the distribution of PA12 powder was more uniform and scattered more evenly. These phenomena were also reflected in the SEM diagram. All samples had a single-peaked distribution except Sample IV, and the distribution of Sample III was very narrow.

In combination with Figure 5, the LLPS region gradually shrank with the increase of DMAC content, which shortened the growth time of polymer droplets and reduced the particle size of PA12 powder. Due to the shortening of coalescence time, the powder formed regular morphology and more uniform dispersion via nucleation and growth mechanism. The T _cloud differed greatly from the T _c, and the growth time of droplets became longer. Small droplets aggregated into larger droplets, which amplified the size of the powder. The LLPS region of Sample I was large, which means that the growth time was the longest. Besides, the powder of Sample I was agglomerated as shown in SEM. Therefore, the D50 value of Sample I was the largest. In addition, the high content of PEG400 made more nucleation points appear in the PA12 chain segment in the solvent, and the crystal growth space was compressed, which hindered the growth of spherulites and formed an imperfect spherulite structure. With the increase of DMAC content, phase diagram (Figure 5) showed that the LLPS region gradually narrows, which shortened the growth time of polymer droplets and reduced the particle size of PA12 powder. Due to the short coalescence time, the powder formed by nucleation growth mechanism had regular morphology and more uniform dispersion. Combined with the analysis of powder morphology and particle size, the powder of Sample III had good sphericity and moderate particle size, which was most suitable for SLS process requirements.

Span value can be used to evaluate the particle size distribution. Powder with a span value of less than 1 can provide high fluidity, which is beneficial for powder spreading performance (36). The volume-weighted cumulative distribution Q₃ diagram is shown in Figure 8. The span values were 3.355, 1.364, 0.863, 1.174, and 0.933. It can be seen that the span value of Sample III was the smallest, and the powder spreading performance was the best.

Figure 8

Volume weighted cumulative distribution Q₃ of PA12 powder.

4.3 XRD

The changes of the crystal structure in PA12 powder and PA12 pellets were analyzed by XRD as shown in Figure 9. The main diffraction peak of the γ crystalline form of PA12 crystals appeared at 2θ = 21.4° (001) crystalline plane, which was found in the PA12 powder and pellets. The difference was α crystalline diffraction at 2θ = 20.2° (200) and around 2θ = 22.7° (010) crystalline plane occurred on the powders. While the γ-crystalline diffraction peak intensity of PA12 powders at 2θ = 11.2° (040) crystalline plane was higher than pellets, which may be due to the orientation of PA12 crystals caused by mechanical stirring shear action during TIPS process (37).

Figure 9

XRD diagram of PA12 powder and PA12 pellets.

4.4 FTIR

The TIPS method modulates the morphological structure of the product mainly via the interaction between solvent and polymer and may not change the molecular structure of the polymer. The FTIR absorbance of PA12 pellets and PA12 powder with different solvent ratios is shown in Figure 10.

Figure 10

FTIR spectra and the characteristic peaks of PA12 powder and PA12 pellet.

Many characteristic bands of γ-PA12 crystals are associated with polar amide and non-polar methylene. The hydrogen-bonded N–H stretching vibration was demonstrated at 3,300 cm⁻¹. The γ-PA12 characteristic peak of amide B was at 3,098 cm⁻¹, while the α-PA12 was at 3,094 cm⁻¹. The amide II bands of γ-PA12 and α-PA12 appeared at 1,565, 1,557, and 1,545 cm⁻¹, respectively. The γ characteristic peak of C═O out-of-plane curvature of the amide VI band appeared at 626 cm⁻¹ (10).

There was no difference in FTIR characteristic peak positions between the powder and pellets, which indicated that TIPS would not change the molecular structure of PA12.

4.5 Crystallization and melting behavior

Sintering window is an important parameter to predict the sintering temperature of the polymer, and the difference between the onset of melting temperature and crystallization temperature. Generally speaking, wide sintering window can improve the accuracy of sintered parts and reduce warpage deformation. The thermal and crystallization behavior of PA12 powders and pellets were characterized by DSC as shown in Figure 11 and Table 3.

Figure 11

DSC diagram of PA12 powder and PA12 pellets.

Table 3

Melting and crystallization characteristics for raw PA12 pellets and prepared PA12 powder

Sample	T _c (°C)	T _c,on (°C)	T _m (°C)	T _m,on (°C)	Melting enthalpy ΔH _m (J · g⁻¹)	SW^a (°C)	Crystallinity χ _c (%)
I	145	149	184	175	82	26	39
II	146	149	184	176	82	27	39
III	145	148	185	177	88	29	42
IV	146	150	187	176	83	26	40
V	146	150	187	176	85	26	41
PA12 pellets	149	151	179	174	51	23	24

^aSW means “sintering window” for SLS processing and was calculated as ΔT = (T _m,on − T _c,on).

According to the data in Table 3, five PA12 powder samples with lower T _c, higher T _m, wider sintering window, and higher melting enthalpy were compared with pellets. Large melting enthalpy can prevent unnecessary sintering of adjacent powders. The sintering window of Sample III was the widest at 29°C, which was higher than the commercially available powder at 19.1°C (PA2200, EOS) (17).

The χ _c of the powder also increased. The polymer chain with high chain mobility and sufficient chain diffusion time because of TIPS process is similar to annealing, which formed higher integrity crystals and thicker lamellae, so as to reduce or eliminate crystal defects to promote crystallization.

The segment entanglement formed in the solvent will be maintained throughout the melting crystallization process. During crystal growth, polymer chains undergo entanglement and massive conformational rearrangement. Once chain entanglement occurs, the movement of polymer chain will be limited, and the crystal growth rate will decrease. The high mobility of the polymer chain in the solvent will disappear when the polymer crystal precipitated from the melt, and the lower crystallization speed of the powder will lead to the decrease of T _c.

4.6 Bulk density

In the SLS process, the bulk density is an important performance index to characterize the performance of PA12 powder. The higher the apparent density, the better the heat transfer performance of the powder in the SLS forming process; the higher the compactness of the formed parts, the better the mechanical properties of the formed parts. The bulk density of polymer powder is related to many factors, such as powder shape, particle size distribution, and the type of polymer material. The morphology of the powder has a great influence on the bulk density.

As shown in Figure 12, the powder of Sample III had the highest bulk density, combined with the morphology. From Figure 7, it can be seen that the powder morphology of Sample III was relatively regular and spherical, so the bulk density was the largest at this time. Therefore, the powder of Sample III had the excellent fluidity so that the sintering parts were more compact.

Figure 12

Plots of bulk density of PA12 powder prepared by TIPS.

4.7 AOR

AOR is often used to characterize the fluidity of powder. The smaller the AOR value, the better the fluidity of the powder in the SLS process, and the higher the precision of the sintered products. The AOR below 30° indicates good fluidity, 30–45° indicates certain adhesiveness. In general, AOR less than 30° represents good flowability in SLS process (38).

As shown in Figure 13, the AOR of the five samples all were lower than 30˚. Therefore, PA12 powder was prepared by the TIPS method with good powder spreading performance during SLS. It can be seen from Figure 13 that AOR values overlap partially within the error range. However, it can be seen only from the average analysis, the AOR of Sample III was the smallest, indicating that the powder of Sample III had the best fluidity. Corresponding to SEM (Figure 7), Sample III had the best sphericity. Conjunction with the bulk density of sample III can conclude that the powder of Sample III will be the most convenient for the desired application of SLS.

Figure 13

AOR of PA12 powder prepared by TIPS.

5 Conclusion

In this article, TIPS method was applied to prepare PA12 powder with suitable size and spherical shape for SLS. DMAC and PEG400 were used as mixed diluents, and the ratio of diluents was changed to control the droplet growth time in the LLPS process to prepare PA12 powder with different particle size distributions. Thermal behavior results and XRD analysis showed that the crystallinity of the powder prepared by TIPS was relatively improved, and the sintering window became wider at 29°C. FTIR results showed that the polymer structure remained unchanged via TIPS process. The AOR and bulk density data of Sample III were the best, indicating that Sample III had excellent powder spreading performance in SLS. This study provides an efficient method to prepare PA12 powder for SLS. Based on this research, the improvement of sintering properties will be further studied.

Funding information: Authors acknowledge the financial support from Science and Technology Program of Guizhou Province (ZK [2022] General 219), the Academic Novice Cultivation and Innovative Exploration Project (GZLGXM-22) supported by Guizhou Provincial Science and Technology Department, and the National Natural Science Foundation of China (Grant No. 52163011).
Author contributions: Dandan Su: writing – original draft, writing – review and editing, formal analysis; Shuhao Qin: writing – original draft, project administration; Jingkui Yang: conceptualization, writing – original draft, formal analysis, writing – review and editing; Lulu Ren: supervision; Shan Liu: date curation, writing – review and editing.
Conflict of interest: Authors state no conflict of interest.
Data availability statement: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Received: 2022-03-10

Revised: 2022-04-24

Accepted: 2022-04-27

Published Online: 2022-06-09

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

https://doi.org/10.1515/epoly-2022-0050

Schlagwörter für diesen Artikel

polyamide 12; selective laser sintering; thermally induced phase separation; cloud point; polymer powder

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