POLYMER COMPOSITION FOR SELECTIVE SINTERING

Abstract

The present invention relates to a polymer composition for production of shaped objects via selective laser sintering wherein the polymer composition comprises a thermoplastic material having: a crystallisation half time of 30 s and 12 min at a supercooling of 50 C. below the peak melt temperature, wherein the crystallisation half time t.sub.1/2,c as determined via differential scanning calorimetry in accordance with ISO 11357-1 (2009); a glass transition temperature T.sub.g of 50 C. as determined in accordance with ISO 11357-2 (2013); a peak melt temperature T.sub.p,m of 200 C. as determined in accordance with ISO 11357-3 (2011), first heating nm; an extrapolated first heating run melt onset temperature T.sub.ei,m of 5 C. above the extrapolated first cooling run crystallisation end temperature T.sub.ef,c as determined in accordance with ISO 11357-1 (2009), first heating and cooling run; and a degree of crystallinity of 10.0% as determined according to the formula (I), wherein: D=degree of crystallinity of the thermoplastic material (%); H.sub.f=enthalpy of fusion of the thermoplastic material as determined in accordance with ISO 11357-3 (2011); H.sub.f,100=enthalpy of fusion of the thermoplastic material in a 100% crystalline state. Such polymer composition has a continuous use temperature of 100 C., and a low change of molecular weight during exposure to selective laser sintering processing temperatures.

[00001]$\begin{array}{cc}D=\frac{.Math..Math.H_f}{.Math..Math.H_{f,100}}100.Math.\%& \left(1\right)\end{array}$

Claims

1. A polymer composition for production of shaped objects via selective sintering wherein the polymer composition comprises a thermoplastic material having: a crystallisation half time of 30 s and 12 min at a supercooling of 50 C. below the peak melt temperature, wherein the crystallisation half time t.sub.1/2,c as determined via differential scanning calorimetry in accordance with ISO 11357-1 (2009); a glass transition temperature T.sub.g of 50 C. as determined in accordance with ISO 11357-2 (2013); a peak melt temperature T.sub.p,m of 200 C. as determined in accordance with ISO 11357-3 (2011), first heating run; an extrapolated first heating run melt onset temperature T.sub.ei,m of 5 C. above the extrapolated first cooling run crystallisation end temperature T.sub.ef,c as determined in accordance with ISO 11357-1 (2009), first heating and cooling run; and a degree of crystallinity of 10.0% as determined according to the formula: $D=\frac{.Math..Math.H_f}{.Math..Math.H_{f,100}}100.Math.\%$ wherein: D=degree of crystallinity of the thermoplastic material (%); H.sub.f=enthalpy of fusion of the thermoplastic material as determined in accordance with ISO 11357-3 (2011); H.sub.f,100=enthalpy of fusion of the thermoplastic material in a 100% crystalline state.

2. The polymer composition according to claim 1 wherein the polymer composition is a powder having an mean particle volume size of 10 and 300 m as determined in accordance with ISO 9276-2 (2014).

3. The polymer composition according to claim 1, wherein the polymer composition is a powder having a D.sub.10 of 5 and 50 m, a D.sub.50 of 60 and 150 m, and a D.sub.90 of 160 and 300 m as determined in accordance with ISO 9276-2 (2014).

4. The polymer composition according to claim 1, wherein the polymer composition comprises 80.0 wt % of the thermoplastic material with regard to the total weight of the polymer composition.

5. The polymer composition according to claim 1, wherein the thermoplastic material is a polyester selected from poly(ethylene terephthalate), poly(ethylene naphthalate), poly(ethylene furanoate), poly(trimethylene terephthalate), poly(ethylene succinate), or poly(hydroxyl butyrate).

6. The polymer composition according to claim 1, wherein the thermoplastic material is poly(ethylene terephthalate).

7. The polymer composition according to claim 5, wherein the thermoplastic material has an intrinsic viscosity of 0.55 and 2.50 dl/g as determined in accordance with ASTM D2857-95 (2007).

8. The polymer composition according to claim 1, wherein the polymer composition further comprises 0.01 wt % and 5.00 wt % with regard to the total weight of the polymer composition of a flow agent selected from silica, alumina, phosphate, borate, titania, talc, mica, kaolin, attapulgite, calcium silicate, magnesium silicate or a combination thereof.

9. A process for production of shaped objects using the polymer composition according to claim 1, wherein the process comprises the steps of: (a) providing a quantity of a powder comprising the polymer composition; (b) irradiating a portion of the polymer composition with an irradiation source such that the particles in that portion of the polymer composition absorb sufficient heat to reach a temperature above T.sub.p,m; (c) terminating the exposure of the portion of the polymer composition to the irradiation source so that the temperature of the particles of the polymer composition decreases to below T.sub.p,m; and (d) removal of the portion of the polymer composition that has not been subjected to irradiation by the energy source; wherein steps (a) through (d) are executed in this sequence.

10. The process according claim 9, wherein the process comprises the steps of: (a) providing a quantity of a powder comprising the polymer composition; (b) irradiating a portion of the polymer composition with a laser energy beam such that the particles in that portion of the polymer composition absorb sufficient heat to reach a temperature above T.sub.p,m; (c) terminating the exposure of the portion of the polymer composition to the irradiation of the laser energy beam so that the temperature of the particles of the polymer composition decreases to below T.sub.p,m; and (d) removal of the portion of the polymer composition that has not been subjected to irradiation by the energy source; wherein steps (a) through (d) are executed in this sequence.

11. The process according to claim 10, wherein: step (a) comprises placing a quantity of powder comprising the polymer composition in a powder bed comprising a horizontal surface and a frame for holding the powder positioned on the surface; step (b) comprises irradiating the portion of the polymer composition by a moving laser energy beam; steps (a), (b) and (c) are repeated in this order to form stacked layers of the polymer composition sintered onto each other prior to execution of step (d).

12. The process according to claims 9-11 wherein the process is performed in an atmosphere comprising 1.0 wt % of oxygen.

13. (canceled)

14. A shaped object produced via the process of any one of claims 9-12.

15. A shaped object according to claim 14, wherein the shaped object has a porosity of 5.0%.

Description

[0056] A particular embodiment of the invention relates to a polymer composition for production of shaped objects via selective laser sintering having a change of Mw of powder before and after selective laser sintering of 25%, more preferable 15%, even more preferable 10%. The Mw after selective laser sintering is to be determined using non-sintered powder.

[0057] Particularly preferably, the invention relates to a polymer composition for production of shaped objects via selective laser sintering having a change of Mw of powder before and after selective laser sintering of 25%, more preferable 15%, even more preferable 10%, wherein the polymer composition comprises a polyester selected from poly(ethylene terephthalate), poly(ethylene naphthalate), poly(ethylene furanoate), poly(trimethylene terephthalate), poly(ethylene succinate), or poly(hydroxyl butyrate). Even more particularly preferably, the invention relates to a polymer composition for production of shaped objects via selective laser sintering having a change of Mw of powder before and after selective laser sintering of 25%, more preferable 15%, even more preferable 10%, wherein the polymer composition comprises a polyester being a poly(ethylene terephthalate) having an intrinsic viscosity of 0.80 dl/g, and 1.50 dl/g, as determined in accordance with ASTM D2857-95 (2007). Using such composition, the crystallinity of the powder does not significantly change despite exposure to high temperature. The first DSC melting peak and the heat of fusion are similar to that of the virgin powder.

[0058] Such polymer composition is advantageous in that it can be used as raw material for a further SLS process in quantities of >50 wt % of the raw material used in such further SLS process, or even >70 wt %.

[0059] A further advantage of a polymer composition comprising such poly(ethylene terephthalate) is that it allows for the selective laser sintering process to be performed at relatively low processing temperatures, which is beneficial as it brings about a reduced electrical power consumption as well as a reduction of charring of the polymer materials.

[0060] The polymer composition according to the present invention may for example comprise a poly(ethylene terephthalate). For example, the polymer composition may comprise 80.0 wt %, alternatively 90 wt %, alternatively 95.0 wt % of a poly(ethylene terephthalate) with regard to the total weight of the polymer composition. The poly(ethylene terephthalate) may be a homopolymer or copolymer. In case the poly(ethylene terephthalate) is a copolymer, the poly(ethylene terephthalate) may for example comprise 15.0 wt %, alternatively 10.0 wt %, alternatively 5.0 wt %, alternatively 2.0 wt %, of units derived from a comonomer, with regard to the total weight of the poly(ethylene terephthalate). Preferably, the poly(ethylene terephthalate) comprises 0.1 wt % and 10.0 wt %, alternatively 0.5 wt % and 5.0 wt % of units derived from a comonomer, with regard to the total weight of the poly(ethylene terephthalate). The units derived from a comonomer may for example be units derived from an aliphatic diol other than ethanediol, for example cyclohexane dimethanol. The units derived from a comonomer may for example be units derived from an aromatic dicarboxylic acid other than terephthalic acid. For example, the aromatic dicarboxylic acid other than terephthalic acid may be isophthalic acid. It is preferred that where the poly(ethylene terephthalate) is a copolymer, it comprises 0.5 wt % and 5.0 wt % of units derived from isophthalic acid, with regard to the total weight of the poly(ethylene terephthalate).

[0061] In a preferred embodiment of the invention, the poly(ethylene terephthalate) has an intrinsic viscosity of 1.00 dl/g and 1.50 dl/g.

[0062] For example, the polymer composition may comprise a thermoplastic material having: [0063] a crystallisation half time of 30 s and 12 min at a supercooling of 50 C. below the peak melt temperature, wherein the crystallisation half time t.sub.1/2,c as determined via differential scanning calorimetry in accordance with ISO 11357-1 (2009); [0064] a glass transition temperature T.sub.g of 50 C. as determined in accordance with ISO 11357-2 (2013); [0065] a peak melt temperature T.sub.p,m of 200 C. as determined in accordance with ISO 11357-3 (2011), first heating run; [0066] an extrapolated first heating run melt onset temperature T.sub.ei,m of 5 C. above the extrapolated first cooling run crystallisation end temperature T.sub.ef,c as determined in accordance with ISO 11357-1 (2009), first heating and cooling run; and [0067] a degree of crystallinity of 10.0% as determined according to the formula:

[00004]$D=\frac{.Math..Math.H_f}{.Math..Math.H_{f,100}}100.Math.\%$

[0068] wherein: [0069] D=degree of crystallinity of the thermoplastic material (%); [0070] H.sub.f=enthalpy of fusion of the thermoplastic material as determined in accordance with ISO 11357-3 (2011); [0071] H.sub.f,100=enthalpy of fusion of the thermoplastic material in a 100% crystalline state

[0072] wherein the thermoplastic material is selected from poly(ethylene terephthalate), poly(ethylene naphthalate), poly(ethylene furanoate), or poly(trimethylene terephthalate), and wherein the polymer composition comprises 90.0 wt % of the thermoplastic material with regard to the total weight of the polymer composition.

[0073] Preferably, the polymer composition comprises 90.0 wt % of poly(ethylene terephthalate) having an intrinsic viscosity of 0.50 dl/g and 1.50 dl/g or 1.00 dl/g and 1.50 dl/g, and the polymer composition is a powder having a mean average particle volume size of 50 m and 200 m as determined in accordance with ISO 9276-2 (2014).

[0074] The polymer composition may in certain embodiments further comprise a flow agent. For example, the polymer composition may comprise 0.01 wt % and 5.00 wt % with regard to the total weight of the polymer composition of a flow agent. Alternatively, the polymer composition may comprise 0.05 and 3.00 wt %, alternatively 0.10 and 1.50 wt, or a flow agent, based on the total weight of the polymer composition. The flow agent may for example be selected from silica, alumina, phosphate, borate, titania, talc, mica, kaolin, attapulgite, calcium silicate, magnesium silicate or a combination thereof. For example, the polymer composition may comprise 0.01 wt % and 5.00 wt % with regard to the total weight of the polymer composition of a flow agent selected from silica, alumina, phosphate, borate, titania, talc, mica, kaolin, attapulgite, calcium silicate, magnesium silicate or a combination thereof.

[0075] In a further embodiment, the present invention also relates to a process for production of shaped objects using the polymer composition according to the invention, wherein the process comprises the steps of: [0076] (a) providing a quantity of a powder comprising the polymer composition; [0077] (b) irradiating a portion of the polymer composition with an irradiation source such that the particles in that portion of the polymer composition absorb sufficient heat to reach a temperature above T.sub.p,m; [0078] (c) terminating the exposure of the portion of the polymer composition to the irradiation source so that the temperature of the particles of the polymer composition decreases to below T.sub.p,m; and [0079] (d) removal of the portion of the polymer composition that has not been subjected to irradiation by the energy source; [0080] wherein steps (a) through (d) are executed in this sequence.

[0081] In a preferred embodiment, [0082] step (a) comprises placing a quantity of powder comprising the polymer composition in a powder bed comprising a horizontal surface and a frame for holding the powder positioned on the surface; [0083] step (b) comprises irradiating the portion of the polymer composition by a moving irradiation source; and [0084] steps (a), (b) and (c) are repeated in this order to form stacked layers of the polymer composition sintered onto each other prior to execution of step (d).

[0085] Particularly, the present invention also relates to a process for production of shaped objects using the polymer composition according to the invention, wherein the process comprises the steps of: [0086] (a) providing a quantity of a powder comprising the polymer composition; [0087] (b) irradiating a portion of the polymer composition with a laser energy beam such that the particles in that portion of the polymer composition absorb sufficient heat to reach a temperature above T.sub.p,m; [0088] (c) terminating the exposure of the portion of the polymer composition to the irradiation of the laser energy beam so that the temperature of the particles of the polymer composition decreases to below T.sub.p,m; and [0089] (d) removal of the portion of the polymer composition that has not been subjected to irradiation by the energy source; [0090] wherein steps (a) through (d) are executed in this sequence.

[0091] In a preferred embodiment, [0092] step (a) comprises placing a quantity of powder comprising the polymer composition in a powder bed comprising a horizontal surface and a frame for holding the powder positioned on the surface; [0093] step (b) comprises irradiating the portion of the polymer composition by a moving laser energy beam; and [0094] steps (a), (b) and (c) are repeated in this order to form stacked layers of the polymer composition sintered onto each other prior to execution of step (d).

[0095] It is preferred that the process is performed in an atmosphere comprising 1.0 wt % of oxygen. In particular it is preferred that the process is performed in an atmosphere comprising 1.0 wt % of oxygen and less than 50 ppm of moisture, more preferably less than 10 ppm oxygen and less than 50 ppm of moisture.

[0096] The thermoplastic materials in the powder bed that is subjected to irradiation are commonly pre-heated to a temperature such that the irradiation energy and time needed to soften the material is minimized, whilst the material remains in a condition that the powder particles that are not subjected to irradiation do not fuse. If the powder bed temperature is too high, it may lead to fusing of the thermoplastic material in undesired locations, resulting in amongst others dimensional inaccuracy of the shaped object. If the powder bed temperature is too low, the thermoplastic material may insufficiently melt in the desired locations, which may result in amongst others undesired porosity of the shaped object. For example, the powder bed temperature may be kept 60 C., more preferable 40 C., even more preferable 10 and 60 C. or 20 and 40 C., below T.sub.p,m.

[0097] In the process according to the present invention, further additives may be applied that may contribute to the selective sintering process. For example, coalescing agents may be added. Such coalescing agents may for example comprise agents that enhance the absorption of the electromagnetic radiation and the conversion of the absorbed energy into thermal energy, thus contributing to the sintering process.

[0098] The present invention also relates to the use of a polymer composition comprising a thermoplastic material having: [0099] a crystallisation half time of 30 s and 12 min at a supercooling of 50 C. below the peak melt temperature, wherein the crystallisation half time t.sub.1/2,c as determined via differential scanning calorimetry in accordance with ISO11357-1 (2009); [0100] a glass transition temperature T.sub.g of 50 C. as determined in accordance with ISO 11357-2 (2013); [0101] a peak melt temperature T.sub.p,m of 200 C. as determined in accordance with ISO 11357-3 (2011), first heating run; [0102] an extrapolated first heating run melt onset temperature T.sub.ei,m of 5 C. above the extrapolated first cooling run crystallisation onset temperature T.sub.ef,c as determined in accordance with ISO 11357-1 (2009), first heating run; and [0103] a degree of crystallinity of 10.0% as determined according to the formula:

[00005]$D=\frac{.Math..Math.H_f}{.Math..Math.H_{f,100}}100.Math.\%$

[0104] wherein: [0105] D=degree of crystallinity of the thermoplastic material (%); [0106] H.sub.f=enthalpy of fusion of the thermoplastic material as determined in accordance with ISO 11357-3 (2011); [0107] H.sub.f,100=enthalpy of fusion of the thermoplastic material in a 100% crystalline state

[0108] in the production of shaped objects via a process comprising the steps of: [0109] (a) providing a quantity of a powder comprising the polymer composition; [0110] (b) irradiating a portion of the polymer composition with a laser energy beam such that the particles in that portion of the polymer composition absorb sufficient heat to reach a temperature above T.sub.p,m; [0111] (c) terminating the exposure of the portion of the polymer composition to the irradiation of the laser energy beam so that the temperature of the particles of the polymer composition decreases to below T.sub.p,m; and [0112] (d) removal of the portion of the polymer composition that has not been subjected to irradiation by the energy source; [0113] wherein steps (a) through (d) are executed in this sequence.

[0114] In further embodiments, the invention relates to shaped objects produced via the process according to the present invention, preferably wherein the shaped object has a porosity of 5.0%. More preferably, the shaped object has a porosity of 4.0%, alternatively 3.0%. The porosity may be determined by comparing the density of an article of the same composition and the same crystallinity produced using the material via SLS (.sub.SLS) with the density of an article produced via injection moulding (.sub.IM). The porosity (P) in % may for example be calculated as:

[00006]$P=\frac{{}_{\mathrm{IM}}-{}_{\mathrm{SLS}}}{{}_{\mathrm{IM}}}100.Math.\%$

[0115] In yet another embodiment, the invention relates to a polymer composition for production of shaped objects via selective sintering wherein the polymer composition comprises a thermoplastic material having: [0116] a crystallisation half time of 30 s and 12 min at a supercooling of 50 C. below the peak melt temperature, wherein the crystallisation half time t.sub.1/2,c as determined via differential scanning calorimetry in accordance with ISO 11357-1 (2009); [0117] a glass transition temperature T.sub.g of 50 C. as determined in accordance with ISO 11357-2 (2013); [0118] a peak melt temperature T.sub.p,m of 200 C. and 300 C. as determined in accordance with ISO 11357-3 (2011), first heating run; [0119] an extrapolated first heating run melt onset temperature T.sub.ei,m of 5 C. above the extrapolated first cooling run crystallisation end temperature T.sub.ef,c as determined in accordance with ISO 11357-1 (2009), first heating and cooling run; and [0120] a degree of crystallinity of 10.0% as determined according to the formula:

[00007]$D=\frac{.Math..Math.H_f}{.Math..Math.H_{f,100}}100.Math.\%$

[0121] wherein: [0122] D=degree of crystallinity of the thermoplastic material (%); [0123] H.sub.f=enthalpy of fusion of the thermoplastic material as determined in accordance with ISO 11357-3 (2011); [0124] H.sub.f,100=enthalpy of fusion of the thermoplastic material in a 100% crystalline state.

[0125] In yet a further embodiment, the invention relates to a polymer composition for production of shaped objects via selective sintering wherein the polymer composition comprises a thermoplastic material having: [0126] a crystallisation half time of 30 s and 12 min at a supercooling of 50 C. below the peak melt temperature, wherein the crystallisation half time t.sub.1/2,c as determined via differential scanning calorimetry in accordance with ISO 11357-1 (2009); [0127] a glass transition temperature T.sub.g of 50 C. as determined in accordance with ISO 11357-2 (2013); [0128] a peak melt temperature T.sub.p,m of 200 C. as determined in accordance with ISO 11357-3 (2011), first heating run; [0129] an extrapolated first heating run melt onset temperature T.sub.ei,m of 5 C. above the extrapolated first cooling run crystallisation end temperature T.sub.ef,c as determined in accordance with ISO 11357-1 (2009), first heating and cooling run; and [0130] a degree of crystallinity of 10.0% as determined according to the formula:

[00008]$D=\frac{.Math..Math.H_f}{.Math..Math.H_{f,100}}100.Math.\%$

[0131] wherein: [0132] D=degree of crystallinity of the thermoplastic material (%); [0133] H.sub.f=enthalpy of fusion of the thermoplastic material as determined in accordance with ISO 11357-3 (2011); [0134] H.sub.f,100=enthalpy of fusion of the thermoplastic material in a 100% crystalline state;

[0135] wherein the polymer composition comprises a polyester selected from poly(ethylene terephthalate), poly(ethylene naphthalate), poly(ethylene furanoate), poly(trimethylene terephthalate), poly(ethylene succinate), or poly(hydroxyl butyrate).

[0136] Preferably, the polymer composition comprises 75.0 wt % of the polyester, more preferable 90.0 wt % or 95.0 wt %, with regard to the total weight of the polymer composition.

[0137] Preferably, the polymer composition comprises 75.0 wt % of the polyester, more preferable 90.0 wt % or 95.0 wt %, with regard to the total weight of the polymer composition, wherein the polyester is a poly(ethylene terephthalate).

[0138] Even further preferably, the polymer composition comprises 75.0 wt % of the polyester, more preferable 90.0 wt % or 95.0 wt %, with regard to the total weight of the polymer composition, wherein the polyester is a poly(ethylene terephthalate) having an intrinsic viscosity of 0.8 dl/g and 1.5 dl/g.

[0139] The invention will now be illustrated by the following non-limiting examples.

TABLE-US-00001 TABLE 1 Materials used Example 1 2 (C) 3 (C) 4 (C) Material type PET PA12 PC PBT D.sub.10 (m) 39 32 40 23 D.sub.50 (m) 94 51 87 60 D.sub.90 (m) 188 82 153 123 Mean particle volume size (m) 107 54 Heat of cold crystallisation None None None None Extrapolated melt onset temperature, first 225 169 214 heating run T.sub.ei,m ( C.) Extrapolated melt end temperature, first 263 184 238 heating run T.sub.ef,m ( C.) Peak melt temperature, first heating run 250 175 226 T.sub.p,m ( C.) Heat of fusion (J/g) 60 91 None 54 Extrapolated crystallisation end temperature, 218 146 * 200 first cooling run T.sub.ef,c ( C.) Peak crystallisation temperature T.sub.p,c ( C.) 210 142 * 191 M.sub.w prior to use in SLS (kg/mol) 124 M.sub.n prior to use in SLS (kg/mol) 47 * The polycarbonate that was used is an amorphous polymer. PET: Polyethylene terephthalate homopolymer, intrinsic viscosity 1.12 dl/g PA12: Polylaurolactam, Duraform PA, obtainable from 3D Ssytems PC: Polycarbonate, Lexan HFD1910, obtainable from SABIC PBT: Polybutylene terephthalate, Valox 195, obtainable from SABIC

[0140] Example 1 presents an embodiment of the present invention, example 2-4 are included for comparative purposes.

[0141] The above materials were subjected to a selective laser sintering process using a Mini-SLS machine comprising a CO.sub.2 laser source. During each laser sintering process, 4 square plates of 30302 mm were produced. To each powder, 0.05 wt % Aerosil 200 flow promoter was added. The materials were pre-dried prior to processing via SLS. The SLS process was conducted in an atmosphere having an oxygen content of 1.0 wt %. The SLS process conditions are presented in table 2. The moisture content of the atmosphere was <50 ppm.

TABLE-US-00002 TABLE 2 SLS processing conditions Example 1 2 (C) 3 (C) 4 (C) Powder bed temperature ( C.) 225 173 140 213 Piston temperature ( C.) 185 135 65 170 Cylinder temperature ( C.) 145 110 65 180 Feed temperature ( C.) 160 120 70 160 Laser power (W) 30 21 21 9 Scan speed (m/s) 4 4 4 4 Hatch distance (m) 150 150 100 100 Layer thickness (m) 100 100 100 100 Laser scanning time (min) 20 20 20 Cooling time (min) 60 10 60

[0142] Of the objects produced via that process, material and article properties were determined as presented in table 3.

TABLE-US-00003 TABLE 3 Material and article properties. Example 1 2 (C) 3 (C) 4 (C) Cold crystallisation temperature ( C.) 133 Heat of cold crystallisation (J/g) 4.2 Peak melting temperature ( C.) 250 Heat of fusion (J/g) 36.7 None Crystallisation half time, supercooling to T.sub.p,m- 10 min 30 s >100 min* 20 s 50 C. Degree of crystallinity 15% * Glass transition temperature T.sub.g midpoint ( C.) 75 Crack resistance + + Dimensional accuracy + + Layer delamination + + + Porosity + + Continuous use temperature + + Powder re-usability + Flexural modulus (MPa)** 2486 1140 Flexural stress (MPa)** 68 67 Gloss at 60 C., in gloss units** 15 1.9 M.sub.w of unused (unsintered) powder (kg/mol) 115 M.sub.w change (%) (decrease) 7.3 M.sub.n of unused (unsintered) powder (kg/mol) 47 M.sub.n change (%) 0 * The polycarbonate was an amorphous polymer. **determined using shaped object

[0143] Wherein:

[0144] The cold crystallisation temperature, the heat of cold crystallisation, the degree of crystallinity, the glass transition temperature, the peak melting temperature, the heat of fusion and the crystallisation half time were determined in accordance with ISO 11357-1 (2009).

[0145] The crack resistance, curling, dimensional accuracy and layer delamination were determined by visual observation.

[0146] Layer delamination is the extent to which the SLS shaped object is resistant to delamination of the formed layer. + indicates a good resistance to delamination, indicates a poor resistance to delamination.

[0147] Dimensional accuracy is the extent to which the obtained shape reflects the desired dimensions. + indicates good dimensional accuracy, indicates poor dimensional accuracy.

[0148] Crack resistance is the extent to which cracks such as cracks due to stress related to shrinkage occur. + indicates good crack resistance, indicates poor crack resistance.

[0149] Porosity was determined by comparing density as described above.

[0150] Flexural stress and flexural modulus were determined in accordance with ASTM D790-15e2 at 23 C.

[0151] Mw and Mn were determined in accordance with ISO 16014-1 (2012).

[0152] Continuous use temperature: + indicates a continuous use temperature 100 C., indicates a continuous use temperature <100 C.

[0153] The above presented examples show that polymer compositions according to the present invention are particularly suitable for the production of shaped objects via selective sintering.

[0154] The DSC curve (first melting) of the SLS printed article of Example 1 showed a T.sub.g at 76 C. (midpoint), a small cold crystallisation endotherm at 133 C. (peak) with heat of 4.2 J/g and a melting endotherm with peak at 250.1 C. and heat of fusion of 36.7 J/g. This confirmed the printed article was crystalline, albeit with a moderate degree of crystallinity. Had the PET article printed from crystalline PET powder been amorphous, the DSC first heating profile of the article would have shown a pronounced T.sub.g at 76 C, a strong cold crystallisation exotherm with typically a heat of 30-35 J/g (instead of 4.2 J/g) and a melting endotherm. Had the PET article been very highly crystalline (as the original PET powder for instance), the DSC curve would have shown a faint T.sub.g, no cold crystallisation peak, and only the melting peak (table 1). The as-printed article with moderate crystallinity was annealed at 200 C. for 2 h. This increased the crystallinity of the article without warpage; the DSC now showed a weaker Tg, no cold crystallisation exotherm, and only the melting peak. If crystallisable polymers with crystallisation half times greater than indicated are used, the resulting articles would be amorphous, thus limiting the softening point and/or continuous use temperature. If crystalline polymers with shorter crystallisation half times are used, the article would be crystalline but controlling warping would have been more difficult.

[0155] The SLS printed article obtained from example 1 showed desirable dimensional accuracy, having desired sharp corners and edges. No curling or delamination occurred. The surface finish was good. Surface gloss was higher than for PA12. The porosity was 3%, which compares to the porosity of SLS printed objects produced using PA12 (example 2), and which is suitable for the production of the desired articles. The dimensional accuracy was desirable, which may be attributed to the crystallisation half time, allowing the crystalline phase formation to proceed not so fast as to induce rapid shrinkage.

[0156] The unused powder obtained from the SLS process in example 1 showed little change of Mw and Mn, indicating that the molecular characteristics of the material were not changed by being subjected to the processing conditions; this indicates that the material can be re-used in a subsequent SLS process, allowing an efficient way of use of the material without extensive waste generation. The samples of example 1 were further subjected to 1H-NMR, which did not show any change of end-group content when comparing powder material before and after SLS.

[0157] When using PA12, as is the case in example 2, the material does show a significant change of molecular weight characteristics, as a result of which the material is rendered unsuitable for re-use in SLS. Furthermore, the low melting point results in the articles not being suitable to be used at desirable high use temperatures.

[0158] The article produced from polycarbonate in example 3 showed high porosity, which is undesirable for many applications of the produced articles. Further, it was amorphous.

[0159] The article produced from PBT in example 4 showed rapid crystallisation, as a result of which the shape stability was poor; undesirable shrinkage occurred, and furthermore the articles were prone to curling and delamination.

[0160] A further test was performed using a quantity of powder of example 1 after subjecting to the SLS process. A material composition comprising 70 wt % PET that was not prior subjected to SLS and 30 wt % PET powder that has been prior subjected to SLS was used to produce a shaped object via SLS according to the conditions presented in table 2. The object that was produced had high dimensional accuracy, sharp edged and low surface roughness.