WO2009154569A1

WO2009154569A1 - Method and system for producing artificial skin

Info

Publication number: WO2009154569A1
Application number: PCT/SG2008/000219
Authority: WO
Inventors: Chonlada Lewis
Original assignee: The Thailand Research Fund; The Prince Of Songkla University; Axis Ip Holding Pte Ltd
Priority date: 2008-06-20
Filing date: 2008-06-20
Publication date: 2009-12-23
Also published as: CN102076365A; CN102076365B

Abstract

Rubber can generally be classified into natural rubber or synthetic rubber. In the field of medical science, one of the more important products manufactured from synthetic rubber is artificial skin. Artificial skin has various uses such as for educational media, for making training aids and phantoms and for covering surfaces of prosthetic limbs. However, it is expensive to produce artificial skin from synthetic rubber. The present invention relates to the utilisation of natural rubber for producing artificial skin for at least reducing the cost of producing artificial skin. A processing method described according to an embodiment of the invention is disclosed. The processing method comprises providing latex, adding a peroxide and a per-compound to the latex for providing depolymerised latex and compounding the depolymerised latex for providing compounded latex whereby the compounded latex is pre-vulcanisable and subsequently vulcanisable into artificial skin.

Description

METHOD AND SYSTEM FOR PRODUCING ARTIFICIAL SKIN

Field Of Invention

The present invention relates generally to rubber technology and utilisation of rubber material. Specifically, the present invention relates to the utilisation of natural rubber for producing artificial skin.

Background

Rubber can generally be classified into two types, namely, natural and synthetic. Natural rubber is obtainable from latex of hundreds of different plant species. However, the most important source of natural rubber is the rubber tree, Hevea brasiliensis. Synthetic rubber, on the other hand, is artificially made from petrochemical feedstock such as crude oil. There exist many types of synthetic rubber for different uses, such as styrene- butadiene rubber, butyl rubber and silicone rubber. Consequently, there exists a wide spectrum of products that range from catheters and condoms to tyres and wetsuits, which are manufactured from both natural and synthetic rubber.

In the field of medical science, one of the more important products manufactured from synthetic rubber is artificial skin. Artificial skin is suitable for use as educational media for medical personnel to practice certain medical procedures including wound sutures, venipuncture and cricothyrotomy. Artificial skin is also an important component in the making of training aids, such as manikins and intravenous (IV) injection arms. The training aids are a good alternative to cadavers for medical personnel to perform dissections and practice procedures.

In the rubber industry today, it is expensive to produce artificial skin from synthetic rubber, such as silicone rubber. As such, many universities and institutions are unable to afford sufficient training aids for their students in the medical science field. Nevertheless, artificial skin is still being manufactured from synthetic rubber instead of natural rubber due to its improved material properties over those of natural rubber.

Besides utilising artificial skin in making training aids and educational media, artificial skin can also be used for making phantoms and for covering surfaces of prosthetic limbs for aesthetic reasons. Prosthetic limbs that appear lifelike and natural enable amputees to cope with emotional trauma associated with limb deficiencies. They also enable amputees to develop a rewarding and satisfying social life. However, phantoms and prosthetic limbs are generally costly as artificial skin is produced from synthetic rubber.

Therefore, there is a need for a method and a system to produce artificial skin from natural rubber for at least reducing the cost of producing artificial skin.

Summary The present embodiment of the invention disclosed herein provides a processing method and a processing system for producing artificial skin from natural rubber for at least reducing the cost of producing artificial skin.

In accordance with a first aspect of the invention, there is disclosed a processing method for processing latex for producing artificial skin. The processing method comprises providing latex having a pre-determined dry rubber content. The processing method also comprises adding a peroxide and a per-compound to the latex for promoting depolymerising thereof and for providing depolymerised latex therefrom. The depolymerised latex has substantially the pre-determined dry rubber content. The processing method further comprises compounding the depolymerised latex for providing compounded latex in which the compounded latex is pre-vulcanisable for providing pre-vulcanised rubber, whereby the pre-vulcanised rubber is initially moldable into a pre-determined shape and subsequently vulcanisable into artificial skin having substantially the pre-determined shape.

In accordance with a second aspect of the invention, there is disclosed a processing system for processing latex for producing artificial skin. The processing system comprises means for receiving latex having a pre-determined dry rubber content and means for adding a peroxide and a per-compound to the latex for promoting depolymerising thereof and for providing depolymerised latex therefrom. The depolymerised latex has substantially the pre-determined dry rubber content. The processing system also comprises means for compounding the depolymerised latex for providing compounded latex in which the compounded latex is pre-vulcanisable for providing pre-vulcanised rubber, whereby the pre-vulcanised rubber is initially moldable into a pre-determined shape and subsequently vulcanisable into artificial skin having substantially the pre-determined shape.

Brief Description Of The Drawings

An embodiment of the invention is described hereinafter with reference to the following drawings, in which:

FIG. 1 shows a process flow diagram of a processing method for processing latex to obtain artificial skin according to an embodiment of the invention;

FIG. 2 shows a flow diagram of latex being processed into artificial skin using the processing method of FIG. 1 ;

FIG. 3 shows a table of average relative molecular masses of depolymerised latex under different conditions using the processing method of FIG. 1 ;

FIG. 4 shows a table of amounts of chemical substances added to the depolymerised latex of FIG. 3;

FIG. 5 shows a table of strength properties of artificial skin obtained using the processing method of FIG. 1 ; and

FIG. 6 shows a system flow diagram of a processing system for processing latex to obtain artificial skin for the processing method of FIG. 1.

Detailed Description

A processing method and a processing system for producing artificial skin from natural rubber are described hereinafter for addressing the aforementioned disadvantage.

For purposes of brevity and clarity, the description of the invention is limited hereinafter to applications relating to producing artificial skin from natural rubber. This however does not preclude various embodiments of the invention from other applications. The fundamental inventive principles of the embodiments of the invention shall remain common throughout the various embodiments.

Exemplary embodiments of the invention described in the detailed description provided hereinafter is in accordance with Fig. 1 to Fig. 6 of the drawings, in which like elements are numbered with like reference numerals.

With reference to Fig. 1 and Fig. 2, a processing method 100 for processing latex 22 is described according to a first exemplary embodiment of the invention. In a step 102, the latex 22 having a pre-determined dry rubber content is provided. The latex 22 has a dry rubber content of preferably 60%. The latex 22 is obtainable from a variety of plants, such as the poinsettia, milkweed plants, rubber figs and rubber trees.

Next in a step 104, a preservation compound 24, such as sodium dodecyl sulphate (C]₂H_2SNaO₄S), is added to the latex 22 for preserving the latex 22. The concentration and amount of sodium dodecyl sulphate added to the latex 22 are preferably 20% m/m aqueous solution and four parts of sodium dodecyl sulphate per hundred parts of the latex 22 by dry mass (4 phr), respectively. The latex 22 is filtered with a sieve prior to adding sodium dodecyl sulphate to the latex 22. The latex 22 and sodium dodecyl sulphate mixture is then stirred for preferably five minutes and is subsequently left to stand for preferably twenty minutes.

Following the step 104, a peroxide 26 and a per-compound 28 are added to the latex 22 mixed with sodium dodecyl sulphate to obtain depolymerised latex 30 therefrom in a step 106. The depolymerised latex 30 has a dry rubber content that is substantially similar to the pre-determined dry rubber content of the latex 22. The peroxide 26 and the per-compound 28 are for promoting depolymerisation of the latex 22. Examples of the peroxide 26 and the per-compound 28 are hydrogen peroxide (H₂O₂) and potassium persulphate (KiS₂Os), respectively. The concentration and amount of hydrogen peroxide added are preferably 30% m/m aqueous solution and two to four parts of hydrogen peroxide per hundred parts of the latex 22 by dry mass (2-4 phr), respectively. Further, the concentration and amount of potassium persulphate added are preferably 10% m/m aqueous solution and five to nine parts of potassium per-sulphate per hundred parts of the latex 22 by dry mass (5-9 phr), respectively.

In the step 106, hydrogen peroxide is added to the latex 22 mixed with sodium dodecyl sulphate and the resulting mixture is stirred for preferably thirty minutes at a speed of preferably sixty revolutions per minute (rpm) and at a temperature of preferably 50-

55⁰C. Subsequently, potassium persulphate is added to the resulting mixture and the resulting mixture mixed with potassium persulphate is stirred for preferably six hours to twenty-four hours at a temperature of preferably 50-55⁰C. The duration of stirring is dependent on the desired relative molecular mass (molecular weight) of the depolymerised latex 30.

The relative molecular mass of the depolymerised latex 30 is obtainable from the intrinsic viscosity of the depolymerised latex 30. The intrinsic viscosity of the depolymerised latex 30 is measurable by an Ubbelohde viscometer. With measurements of the intrinsic viscosity of the depolymerised latex 30, the relative molecular mass of the depolymerised latex 30 can be calculated from the Mark-Houwink Equation as follows:

η = KM^a

in which η represents intrinsic viscosity of a polymer, M represents average relative molecular mass of the polymer, and K and a are experimentally determinable constants.

Fig. 3 shows a table of average relative molecular masses of the depolymerised latex 30 obtained from the intrinsic viscosity of the depolymerised latex 30 corresponding with different durations of stirring the resulting mixture mixed with potassium persulphate at room temperature and at a temperature of substantially 50-55^ϋC. In this specific example, the intrinsic viscosity of the depolymerised latex 30 is measured by an Ubbelohde viscometer. Additionally, the amount of hydrogen peroxide added to the latex 22 mixed with sodium dodecyl sulphate is substantially two parts of hydrogen peroxide per hundred parts of the latex 22 by dry mass (2 phr) whereas the amount of potassium persulphate added is substantially 8.1 parts per hundred parts of the latex 22 by dry mass (8.1 phr).

The average relative molecular mass of the depolymerised latex 30 is reduced to a greater extent when stirring of the resulting mixture with potassium persulphate is carried out at a temperature of substantially 50-55⁰C than at room temperature. With reference to Fig. 3, when the duration of stirring is 6 hours, the average relative molecular masses of the depolymerised latex 30 at room temperature and at a temperature of substantially 50-55⁰C are 490,800 and 160,886, respectively. When the duration of stirring is increased to twelve hours, the average relative molecular masses of the depolymerised latex 30 at room temperature and at a temperature of substantially 50- 55⁰C are 432,600 and 101,582, respectively. The average relative molecular masses of the depolymerised latex 30 are 296,450 and 88,524 at room temperature and at a temperature of substantially 50-55⁰C, respectively, when the duration of stirring is further increased to eighteen hours. Further, when the duration of stirring is increased to twenty-four hours, the corresponding average relative molecular masses of the depolymerised latex 30 are 266,200 and 68,400 at room temperature and at a temperature of substantially 50-55⁰C, respectively.

The desired average relative molecular mass of the depolymerised latex 30 is substantially between 60,000 to 100,000. To obtain an average relative molecular mass of the depolymerised latex 30 that falls between 60,000 to 100,000, the duration of stirring needs to be substantially more than twenty-four hours when stirring is carried out at room temperature. However, at a temperature of substantially 50-55⁰C, the duration of stirring takes between twelve to twenty-four hours to obtain an average relative molecular mass of the depolymerised latex 30 that falls between 60,000 to 100,000. Thus, the temperature at which the stirring is carried out is preferably at a temperature of substantially 50-55⁰C instead of at room temperature, as the duration of stirring is shorter.

Following the step 106, pH of the depolymerised latex 30 is adjusted to substantially pH 9 in a step 108. The depolymerised latex 30 is preferably cooled from a temperature of substantially 50-55⁰C to room temperature prior to the adjustment of pH. Determination of the dry rubber content of the depolymerised latex 30 is preferably carried out after the pH of the depolymerised latex 30 is adjusted for calculating the amounts of chemical substances 32 that need to be added to the depolymerised latex 30. Alkalis, such as potassium hydroxide (KOH), are used to adjust the pH of the cooled depolymerised latex 30 and the concentration of potassium hydroxide used is substantially 10% m/m aqueous solution.

Next in a step 1 10, after adjusting the pH of the depolymerised latex 30, chemical substances 32 are compounded with the depolymerised latex 30 to obtain compounded latex 34. The chemical substances 32 are in the form of dispersion or emulsion before the chemical substances 32 are mixed with the depolymerised latex 30. The chemical substances 32 comprise sulphur in the form of dispersion, zinc diethyldithiocarbamate (ZDEC) in the form of dispersion, sodium dithiocarbamate in the form of liquid, spindle oil in the form of emulsion, calcium carbonate (CaCO₃) in the form of dispersion, zinc oxide (ZnO) in the form of dispersion and Vulkanox BKF in the form of dispersion. The concentration of dispersion of sulphur, ZDEC, CaCO₃, ZnO and Vulkanox BKF are substantially 50% m/m, and the concentration of emulsion of spindle oil is substantially 50% m/m.

Fig. 4 shows a table illustrating the preferably amounts of each of the chemical substances 32 described above to be added to the depolymerised latex 30. Firstly, the depolymerised latex 30 is stirred for preferably five minutes before the chemical substances 32 are added. Subsequently, substantially 1.5 parts of dispersion of sulphur per hundred parts of the depolymerised latex 30 by dry mass (1.5 phr) is added to the depolymerised latex 30 and stirred for substantially five minutes. Next, substantially one part of dispersion of ZDEC per hundred parts of the depolymerised latex 30 by dry mass (1 phr) and one part of liquid of sodium dithiocarbamate per hundred parts of the depolymerised latex 30 by dry mass (1 phr) are added and stirred for substantially five minutes.

Subsequently, substantially 7.5 parts of emulsion of spindle oil per hundred parts of the depolymerised latex 30 by dry mass (7.5 phr) is added and stirred for preferably five minutes. This is followed by the addition of substantially twenty parts of 50% CaCO₃ dispersion per hundred parts of depolymerised latex 30 by dry mass (20 phr) and stirring for substantially five minutes thereafter. Finally, substantially 5 parts of dispersion of ZnO and one part of dispersion of Vulkanox BKF per hundred parts of depolymerised latex 30 by dry mass (5 phr and 1 phr), respectively, are added to the depolymerised latex 30 and stirred for substantially thirty minutes to obtain the compounded latex 34. The compounded latex 34 is then continuously stirred for substantially 24 hours and filtered with a sieve thereafter.

Next in a step 1 12, the compounded latex 34 is pre-vulcanised at a temperature of preferably 70⁰C for substantially one hour to provide pre-vulcanised rubber 36. Following the step 1 12, the pre-vulcanised rubber 36 is initially moldable into a predetermined shape and subsequently vulcanisable into artificial skin 38 having the predetermined shape in a step 1 14. The pre-vulcanised rubber 36 is moldable using a mold of a desired shape. The pre-vulcanised rubber 36 is heated at a temperature of preferably between 50⁰C to 100⁰C after the pre-vulcanised rubber 36 is cast in the mold of the desired shape to obtain the artificial skin 38.

The artificial skin 38 obtained from the processing method 100 has a shore hardness of preferably 42-47 Shore A, a tensile strength of preferably 5-10 MPa and a stiffness of preferably 20-35 N/mm. Fig. 5 shows a table of strength properties of the artificial skin 38 after the pre-vulcanised rubber 36 is heated at a temperature of substantially 70⁰C for substantially ten hours. In this example, the artificial skin 38 has strength properties of a shore hardness of substantially 42 Shore A, a tensile strength of substantially 4.03 MPa, an elongation before breakage of substantially 434% and a stiffness of substantially 21.81 N/mm.

The artificial skin 38 is suitable for use as education media for medical personnel to practice certain medical procedures including wound sutures, venipuncture and cricothyrotomy. The artificial skin 38 is also suitable for making training aids, such as manikins and intravenous (IV) injection arms.

According to a second exemplary embodiment of the present invention, a processing system 400 is provided for the implementation of the processing method 100. The processing system 400 comprises means for receiving the latex 402. The processing system 400 also comprises means for adding the preservation compound to the latex 404 for performing the step 104, and means for obtaining the depolymerised latex 406 for performing the step 106. The processing system 400 comprises means for adjusting the pH of the depolymerised latex 408 for performing the step 108, as well as means for obtaining the compounded latex 410 for performing the step 1 10. The processing system 400 further comprises means for pre-vulcanising the compounded latex 412 and means for obtaining the artificial skin 414 for performing the step 1 12 and the step 1 14, respectively.

In the foregoing manner, a processing method and a processing system for processing latex are described according to exemplary embodiments of the invention for addressing the foregoing disadvantage of conventional methods and systems. Although only a few embodiments of the invention are disclosed, the invention is not to be limited to the specific forms or arrangements of parts so described and it will be apparent to one skilled in the art in view of this disclosure that numerous changes and/or modification can be made without departing from the scope and spirit of the invention.

Claims

1. A processing method for processing latex for producing artificial skin, comprising: providing latex having a pre-determined dry rubber content; adding a peroxide and a per-compound to the latex for promoting depolymerising thereof and for providing depolymerised latex therefrom, the depolymerised latex having substantially the pre-determined dry rubber content; and compounding the depolymerised latex for providing compounded latex, wherein the compounded latex is pre-vulcanisable for providing pre- vulcanised rubber, whereby the pre-vulcanised rubber is initially moldable into a predetermined shape and subsequently vulcanisable into artificial skin having substantially the pre-determined shape.

2. The processing method as in claim 1 , providing latex having a pre-determined dry rubber content comprising: adding a preservation compound to the latex.

3. The processing method as in claim 1 , wherein the pre-determined dry rubber content is substantially sixty percent.

4. The processing method as in claim 2, wherein the preservation compound is sodium dodecyl sulphate.

5. The processing method as in claim 4, wherein the preservation compound is used in an amount of substantially four parts per hundred parts of the latex by dry mass.

6. The processing method as in claim 2, providing latex having a pre-determined dry rubber content further comprising: filtering of the latex prior to adding the preservation compound to the latex.

7. The processing method as in claim 1, wherein the peroxide is hydrogen peroxide and the per-compound is potassium per-sulphate.

8. The processing method as in claim 7, wherein the peroxide is used in an amount of from substantially two to four parts per hundred parts of the latex by dry mass and the per-compound is used in an amount of from substantially five to nine parts per hundred parts of the latex by dry mass.

9. The processing method as in claim 1, adding a peroxide and a per-compound to the latex for promoting depolymerising thereof comprising: obtaining the depolymerised latex having an average relative molecular mass of from 60,000 to 100,000.

10. The processing method as in claim 9, further comprising: adjusting the pH of the depolymerised latex to substantially pH 9 prior to compounding the depolymerised latex for providing the compounded latex.

1 1. The processing method as in claim 1, compounding the depolymerised latex for providing compounded latex comprising: adding sulphur, zinc diethyldithiocarbamate, sodium dithiocarbamate, spindle oil, calcium carbonate, zinc oxide and vulkanox BKF to the depolymerised latex.

12. The processing method as in claim 1 1 , wherein the sulphur, zinc diethyldithiocarbamate, sodium dithiocarbamate, spindle oil, calcium carbonate, zinc oxide and vulkanox BKF are used in amounts of substantially 1.5 parts, 1 part, 1 part, 7.5 parts, 20 parts, 5 parts and 1 part per hundred parts of the depolymerised latex by dry mass, respectively.

13. The processing method as in claim 1 1, further comprising: filtering the compounded latex.

14. The processing method as in claim 1, wherein the compounded latex is pre- vulcanisable at a temperature of substantially 70⁰C for providing the pre- vulcanised rubber.

15. The processing method as in claim 1, wherein the pre-vulcanised rubber is vvuullccaanniisable into artificial skin at a temperature of substantially from 50⁰C to 100⁰C.

16. The processing method as in claim 1 , further comprising: pre-vulcanising the compounded latex for providing the pre-vulcanised rubber.

17. The processing system as in claim 1 , further comprising: vulcanising the pre-vulcanised rubber into artificial skin.

18. A processing system for processing latex for producing artificial skin, comprising: means for receiving latex having a pre-determined dry rubber content; means for adding a peroxide and a per-compound to the latex for promoting depolymerising thereof and for providing depolymerised latex therefrom, the depolymerised latex having substantially the pre-determined dry rubber content; and means for compounding the depolymerised latex for providing compounded latex, wherein the compounded latex is pre-vulcanisable for providing pre- vulcanised rubber, whereby the pre-vulcanised rubber is initially moldable into a pre- determined shape and subsequently vulcanisable into artificial skin having substantially the pre-determined shape.

19. The processing system as in claim 18, means for receiving latex having a predetermined dry rubber content comprising: means for adding a preservation compound to the latex.

20. The processing system as in claim 18, wherein the pre-determined dry rubber content is substantially sixty percent.

21. The processing system as in claim 19, wherein the preservation compound is sodium dodecyl sulphate.

22. The processing system as in claim 21, wherein the preservation compound is used in an amount of substantially four parts per hundred parts of the latex by dry mass.

23. The processing system as in claim 19, means for receiving latex having a predetermined dry rubber content further comprising: means for filtering of the latex prior to adding the preservation compound to the latex.

24. The processing system as in claim 18, wherein the peroxide is hydrogen peroxide and the per-compound is potassium per-sulphate.

25. The processing system as in claim 24, wherein the peroxide is used in an amount of from substantially two to four parts per hundred parts of the latex by dry mass and the per-compound is used in an amount of from substantially five to nine parts per hundred parts of the latex by dry mass.

26. The processing system as in claim 18, means for adding a peroxide and a per- compound to the latex for promoting depolymerising thereof comprising: means for obtaining the depolymerised latex having an average relative molecular mass of from 60,000 to 100,000.

27. The processing system as in claim 26, further comprising: means for adjusting the pH of the depolymerised latex to substantially pH 9 prior to compounding the depolymerised latex for providing the compounded latex.

28. The processing system as in claim 18, means for compounding the depolymerised latex for providing compounded latex comprising: means for adding sulphur, zinc diethyldithiocarbamate, sodium dithiocarbamate, spindle oil, calcium carbonate, zinc oxide and vulkanox BKF to the depolymerised latex.

29. The processing system as in claim 28, wherein the sulphur, zinc diethyldithiocarbamate, sodium dithiocarbamate, spindle oil, calcium carbonate, zinc oxide and vulkanox BKF are used in amounts of substantially 1.5 parts, 1 part, 1 part, 7.5 parts, 20 parts, 5 parts and 1 part per hundred parts of the depolymerised latex by dry mass, respectively.

30. The processing system as in claim 28, further comprising: means for filtering the compounded latex.

31. The processing system as in claim 18, wherein the compounded latex is pre- vulcanisable at a temperature of substantially 70⁰C for providing the pre- vulcanised rubber.

32. The processing system as in claim 18, wherein the pre-vulcanised rubber is vulcanisable into artificial skin at a temperature of substantially from 50⁰C to

100⁰C.

33. The processing system as in claim 18, further comprising: means for pre-vulcanising the compounded latex for providing the pre- vulcanised rubber.

34. The processing system as in claim 18, further comprising: means for vulcanising the pre-vulcanised rubber into artificial skin.