Method for making a three dimensional object

Abstract

The present invention relates to a method for making a three dimensional carbon structure and also to a sintered article comprising pyrolysed carbon particles. The method comprises sintering a powdered organic material, preferably using selective laser sintering, to form a sintered three dimensional structure having a desired shape. The sintered structure is then pyrolysed to form the final carbon structure. The method is particularly useful in the production of biomedical implants such as bone scaffolds and joint replacements. In some embodiments, the powdered organic material is lignin which provides a renewable and highly cost effective starting material for the method of the present invention.

Claims

1. A method of making a carbon structure, the method comprising sintering a powdered organic polymer to form a sintered first structure and pyrolysing the sintered first structure to convert it to the carbon structure, wherein the sintering step is an additive manufacturing process and wherein the powdered organic polymer comprises, at 50% or more by weight of the total material that is sintered, (i) a carbohydrate and/or (ii) lignin or a salt or derivative thereof.

2. The method of claim 1, wherein the carbohydrate is cellulose or a derivative thereof.

3. The method of claim 1, wherein the powdered organic polymer has a particle size of no more than 0.125 mm.

4. The method of claim 1, wherein an additive is included with the powdered organic polymer prior to sintering, which additive comprises at least one of: (i) a reinforcement (ii) a filler intended to remain in the final structure and (iii) an additive that is degradable to form pores.

5. The method of claim 4 wherein the reinforcement is selected from carbon fibre, a material that will form carbon fibres at the sintering temperature, and titanium, and/or wherein the filler is selected from ceramic, glass and carbon particles.

6. The method of claim 4, wherein the additive is degradable and the method comprises degrading the additive to form pores in the carbon structure.

7. The method of claim 1, wherein sintering is carried out using a laser or an electron beam.

8. The method of claim 1, wherein sintering is carried out at a temperature of from 130 C. to 300 C.

9. The method of claim 1, wherein pyrolysis is carried out at a temperature of from 200 C. to 3000 C., and/or for a period of from 30 seconds to 48 hours.

10. The method of claim 1, further comprising heating the carbon structure at a temperature greater than the temperature used to convert the sintered first structure to the carbon structure, thereby producing a structure comprising pyrolytic carbon.

11. The method of claim 1, wherein the carbon structure is at least 95% carbon by weight.

12. The method of claim 1, wherein the carbon structure comprises an outer shell that is at least 95%, carbon by weight and an inner core comprising sintered organic polymer that has not undergone pyrolysis.

13. A method of making a carbon structure, comprising: sintering a powdered organic polymer to form a sintered first structure using an additive manufacturing process, wherein the powdered organic polymer comprises, at 50% or more by the weight that is sintered, (i) a carbohydrate and/or (ii) lignin or a salt or derivative thereof; and pyrolysing the sintered first structure to convert it to the carbon structure.

14. The method of claim 13, further comprising: heating the carbon structure at a temperature greater than the temperature used to convert the sintered first structure to the carbon structure, thereby producing a structure containing pyrolytic carbon.

Description

EXAMPLE 1SINTERING OF ORGANIC POLYMERS

(1) Materials

(2) Two types of organic polymer powder were used for comparison: Arboform 45 (available from Tecnaro GmbH) and Lignabond DD (available from Borregaard AS). Arboform 45 consists largely of lignin and cellulose. Lignabond DD consists of lignosulphonate.

(3) Preparation of Organic Polymer Powder

(4) Both powders were sieved using 120 weight mesh resulting in particle sizes of no more than 0.125 mm in diameter.

(5) Preparation of Airtight Container

(6) The melting point and combustion point of Lignobond DD are within 30 C. and therefore it was decided that powder should be heated in a controlled environment in the absence of oxygen.

(7) In order to prepare an airtight container, small tinfoil pouches were filled with organic polymer powder and sealed so that the powder formed a layer approximately 0.5 to 3 mm thick. The opening of the pouch was folded until it was tight against the powder in order to prevent oxidation as a result of exposure to free oxygen in the airspace of the container. However, the pouch provided no significant compressive force on the powder.

(8) Sintering Method

(9) An oven was pre-heated to 175 C. and eight airtight tinfoil pouches filled with organic polymer powder (four of each brand) were inserted and left in the ambient heat. After six hours four pouches were removed (two of each brand). After twelve hours the remaining four pouches were removed (two of each brand).

(10) Results

(11) All eight samples were successfully sintered (i.e. the particles of powder had fused to form a single mass). This was determined using a visual inspection. There was no significant difference between the six hour and twelve hour samples except for a darkening of the powder in the twelve hour samples. Some difference between the Arboform 45 and Lignabond DD samples was observed. This is believed to result from additives present in Arboform 45 which are incorporated to make it appropriate for an injection moulding process.

EXAMPLE 2PYROLYSIS OF SINTERED ORGANIC POLYMER

(12) Method

(13) Four of the sintered samples produced in Example 1 (one of each brand from each duration in the sintering oven) were placed in an airtight container (this held a pocket of approx. 300 ml of air hence 370 mg of available O.sub.2) and placed into an oven preheated to 200 C. for two hours.

(14) Results

(15) All samples pyrolysed successfully, as determined by visual inspection, and had turned to carbon. There is no discernible difference between the Arboform 45 or Lignabond DD samples once pyrolysed.

(16) Summary

(17) The above Examples demonstrate that a powdered organic polymer can be sintered and pyrolysed to form a sintered, pyrolysed carbon structure. In these Examples, it was found that the powder should be housed in a controlled environment with insufficient oxygen to allow any substantial oxidation/combustion to occur. Both brands of organic polymer powder appeared to sinter equally well with no discernible difference in the carbon produced once they had gone through the process of pyrolysis. In addition, comparison of the sintered lignin powder and pyrolysed carbon with low level sintered titanium shows a very similar consistency across all three materials at this low temperature sintering point.