FIELD OF INVENTION

[0001] The present invention generally relates to self-healing materials, and more particularly to a wearable self-healing article and method of making the wearable self-healing article.

BACKGROUND

[0002] Commercially available rubber gloves’ longevity or lifespan depends on the type of work they are used for, in which typically these gloves do not last long especially if worn daily or for handling heavy loads and hazardous substances. Justifiably, wear and tear results to shorter lifespan of the glove. Further physical damages may cause dermal exposure to chemicals or abrasive materials that could be hazardous to the wearer’s health. The surging awareness towards glove wearer’s safety - particularly forthose who are employed in the chemical, food, agriculture or healthcare industry - have boosted the demand for industrial gloves of superior features and reusable benefits.

[0003] Accordingly, there is a need to find a sustainable and facile way of making reusable gloves to meet the increasing demand.

SUMMARY

[0004] In one aspect the present invention provides a method for making a self-healing glove comprising the steps of: a) dipping a former in a coagulant mixture to deposit a coagulant layer on the former; b) drying the former with the deposited coagulant layer; c) dipping the former with the deposited coagulant layer in a rubber mixture to deposit a rubber layer on the former; d) drying the former with the deposited rubber layer; characterised in that: steps a-d are repeated for more than two cycles to form a single rubber layer; the rubber layer including a nanofiller comprising cellulose nanofiber.

[0005] Advantageously, the nanofiller allows self-healing of the article if it is damaged. [0006] In one embodiment, the method further includes the steps of subjecting the former to a beading process; drying the former; dipping the former in a polymer coating to form an article; and stripping the article from the former.

[0007] In one embodiment, the rubber mixture comprises epoxidized natural rubber, natural rubber, a surfactant, a vulcanizer, an accelerator, an organic peroxide and a nanofiller. Typically, the nanofiller comprises Zinc Oxide Carbon Nano Fiber (ZnO-CNF).

[0008] In an embodiment, the nanofiller is prepared from oil palm empty fruit bunches.

[0009] In an embodiment the coagulant mixture comprises calcium nitrate ((CaNO ) and calcium carbonate (CaCOa).

[0010] In one embodiment step (a) of dipping the former in the coagulant mixture includes a dwelling time of 20 seconds. Typically, the former with the deposited rubber layer is dried for 30 minutes at a temperature of 100°C.

[0011] In a further aspect, the present invention provides a wearable self-healing article comprising a rubber layer that reconstructs under a thermal condition of 80°C temperature for a duration of one hour.

[0012] In an embodiment, the thermal treatment further includes subsequently relaxing the article in room temperature.

[0013] Advantageously, relaxing in room temperature allows the article to self-heal.

[0014] In an embodiment, the rubber layer comprises epoxidized natural rubber (ENR)

[0015] Advantageously, the ENR chains restriction diminishes under the thermal condition which accelerates the self-healing process.

[0016] In yet another embodiment, the rubber layer further comprises a nanofdler. The nanofiller includes cellulose nanofiber. Typically, the nanofiller is ZnO-CNF.

[0017] Advantageously, the Zn ²⁺ salt ions from the ZnO-CNF interacts with the oxygenous groups along the ENR chain once the restriction of ENR chain is diminished and a bond between the ENR chain and Zn ²⁺ salt ion is created during the self-healing process. BRIEF DESCRIPTION OF DRAWINGS

[0018] The invention will be more understood by reference to the description below taken in conjunction with the accompanying drawings herein:

[0019] FIG. 1 provides a flowchart of the method in accordance with an embodiment of the present invention;

[0020] FIG. 2 shows the self-healing mechanism in accordance with an embodiment of the present invention;

[0021] FIG. 3 depicts self-healing assessment results based on experimental examples: (A) Stressstrain curve of varying durations of thermal (80°C) and room temperature healing. (B) Repeated self-healing cycles. Optical microscopy photograph of (C) freshly cuts sample. (D) healed sample after thermal exposure. Field emission scanning electron microscope (FESEM) image (E) freshly cut sample and (F) FESEM image after heal

[0022] FIG. 4 depicts another self-healing assessment based on an experimental example: (A) Glove air leakage experimental setup. (B) NR and self-healing (S-H) gloves were inflated with air, indicating no holes before the experiment. (C) S-H and NR gloves were cut across, approximately 50 mm in length. (D) The cut surfaces of both gloves were marked. (DI) Focused image of S-H glove cut surface. (E) Air escaping through the cut. (F) Healed surface after 1 hour at 80 °C, and 3 hours relaxed at room temperature. (Fl) Focus image of healed S-H glove. (G) Deflated S-H glove.

DETAILED DESCRIPTION

[0023] In line with the above summary, the following description of a number of specific and alternative embodiments is provided to understand the inventive features of the present invention. It shall be apparent to one skilled in the art, however that this invention may be practiced without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures. [0024] Embodiments of the invention are described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the scope of the present invention. It should be noted that the drawings include schematic description of how the process in accordance with the preferred embodiments can be carried out. The standard equipment which may be used to carry out the method of the present invention may have not been illustrated since they are known in the art.

[0025] In one embodiment, the present invention provides a method for making a self-healing article, whereby the article includes a single rubber layer that reconstructs under athermal condition. The rubber layer is formed from a rubber mixture that includes a nanofiller as a base reinforcement material for the self-healing article.

[0026] The rubber mixture comprises ENR, natural rubber, a surfactant, a vulcanizer, an accelerator, an organic peroxide and a nanofiller prepared from sustainable resources. In the preferred embodiment, the rubber mixture may be prepared in accordance with a formulation as shown in TABLE 1 below:

TABLE 1

Example of Formulation for Rubber Mixture

[0027] In accordance with the preferred embodiment, the chemicals above are added and mixed in a container consisting of latex overnight prior to the dipping process. The method further includes preparing a coagulant mixture in the form of a solution comprising 15% calcium chloride (CaNCh ) and 5% calcium carbonate (CaCCF).

[0028] The nanofiller is a cellulose-based nanofiller prepared from oil palm empty fruit bunches, whereby in the preferred embodiment, the nanofiller comprises Zinc Oxide (ZnO) and cellulose nanofiber (CNF). The ZnO-CNF nanofiller may be prepared according to known or conventional methods for producing ZnO-CNF slurry to be added to the rubber mixture. In a preferred embodiment, the average particle width or diameter of cellulose is 25 nm and fibre length ranges between 900 nm - 1000 nm.

[0029] An example of preparing the nanofiller is as shown in EXAMPLE 1 below.

EXAMPLE 1

Synthesis Of The Cellulose-Based Nanofiller For The Rubber Reinforcement

[0030] In brief, 1 g of freeze-dried CNF was measured and stirred in 200 ml of ultrapure water0.44 g of Zn(CH3COO)2 -2H2O was then added to the CNF suspension, magnetically stirred at a speed of 500 rpm for 1 h. The CNF mixture was then treated with pulsed ultrasonication at 20 kHz and 100 W for 5 minutes. The CNF suspension was transferred into a three-necked refluxing flask comprised of a Liebig condenser and refluxed at 90 °C for 1 h using a heating mantle. The temperature of the CNF suspension was monitored using a digital thermometer. Next, 100 mM of NaOH was added to the suspension, and the pH of the adjusted to 10 using 1 M HC1 and 1 M NaOH solutions. The mixture was then continuously stirred for 30 minutes at a speed of 500 rpm and later subjected to ultrasonication treatment for an additional 5 minutes. The obtained ZnO-CNF suspension was fdtered using standard vacuum fdtration apparatus. The filtered ZnO-CNF was rinsed with ethanol and ultrapure water for at least four cycles to remove any residual chemicals. The wet ZnO-CNF slurry was immediately added to ENR latex mixture for further processing.

[0031] In accordance with the preferred embodiment of the present invention, the concentration of the coagulant and rubber mixture may vary, and additives (not mentioned herein) may be added if required. The parameters and conditions of the method for making the self-healing article may be calculated using known or conventional methods. [0032] According to a preferred embodiment, the polymer coating comprises com flour and distilled water. The coating is applied as an interior layer for ease of glove stripping from the former and during glove donning.

[0033] With reference to FIG.l, the method of the present invention comprises the steps of dipping a former in a coagulant mixture to deposit a coagulant layer on the former (S 101); drying the former with the deposited coagulant layer (SI 02); dipping the former with the deposited coagulant layer in a rubber mixture to deposit a rubber layer on the former (S 103); drying the former with the deposited rubber layer (S104); subjecting the former to a water leaching process (S105); subjecting the former to a beading process (S 106); dipping the former in a polymer coating to form an article (S107); and stripping the article from the former (S108). In the preferred embodiment, at least three cycles of dipping the former with coagulant in a rubber mixture to drying the former with deposited with rubber layer are carried out prior to a water leaching process.

[0034] In accordance with the preferred embodiment, the step of dipping the former in the coagulant includes a dwelling time of 20 seconds, followed by drying at a predetermined high temperature for lO minutes. The former is then dipped in the rubber mixture for 30 seconds to ensure uniform coating of the rubber mixture, prior to drying the former coated with rubber mixture for 30 minutes at high temperature. It should be noted however that the dipping and dwelling time in the coagulant and rubber mixture may vary.

[0035] The above three steps are repeated for at least three cycles before the former is subjected to the next steps, being a water leaching process, beading process, dipping the former in a polymer coating mixture and stripping the article from the former.

[0036] An experimental example of making the self-healing article is shown under EXAMPLE 2 below:

EXAMPLE 2

Preparing Self-Healing Glove

[0037] A small ceramic hand former with a length of 15 cm was used to fabricate the self-healable glove. The total wet weight of ENR latex used for the dipping process was 400 - 600 g. The latex dipping formulation was prepared following the same formulation in Table 1. The coagulation solution used in this experiment consists of 15% calcium nitrate (CaNCh and 5% calcium carbonate (CaCOft. The desired amount of com starch was dispersed in water and used as the polymer coating for ease of glove stripping from the hand former. Firstly, the hand former was thoroughly cleaned using acid (I M HC1), alkali (I M NaOH) and washed with water to remove any residues or dirt. Next, the cleaned ceramic former was dipped into the coagulant with a dwelling time of 20 seconds. Then, the former was dried in a non-aerated oven at 100 °C for 10 minutes. The ceramic former was then dipped into ENR/ZnO-CNF latex slurry for 30 seconds. The latex dipped former was then slowly rotated manually to ensure uniform coating of the ENR latex mixture. The former was dried again in the oven for 30 minutes at 100 °C. The coagulation dipping to latex dipping and drying process was repeated over three cycles. The dipping process was slightly modified in this study to obtain the prototype glove having a thickness of 0.40 - 0.50 mm, comparable to a general reusable glove. After the three cycles, the hand former was removed from the oven and proceeded with water leaching, at a temperature of 70 °C for 1 minute, and followed by the glove beading process. Next, the hand former was heated to 110 °C for 20 to 30 minutes till dryness. The former was then dipped into the polymer coating for 5 to 10 seconds. The glove prototype would subsequently be stripped off the hand former and left to dry at room temperature.

[0038] In another aspect, the present invention provides a wearable self-healing article that includes a single rubber layer which reconstructs under a thermal condition. In the preferred embodiment, the self-healing article is a glove.

[0039] The thermal condition includes a heat treatment at a temperature of at least 80°C for one hour after which the layer is reconstructed or healed at room temperature.

[0040] In a further aspect, the present invention provides a self-healing glove that includes a rubber layer in which the tensile strength can be recovered up to 65 - 69% and 85 - 90% respectively, at room temperature.

[0041] With reference to the experimental examples, it is observed that the recovery strength is increased up to 2.5 - 3.5 MPa, which was 65 - 69% of its original value of 4. 1 - 5.2 MPa and 85 - 92% of strain recovery was observed after the thermal treatment at 80 °C for 1 hour and subsequently at room temperature for 3 hours, compared to 32.5% of its original tensile strength after healing for 24 hours at room temperature. With respect to the self-healing cycle, the tensile strength and strain values of ENR/ZnO-CNF 5 per hundred rubber (phr) composite decreased to 1.3 MPa and 391.6% in the second healing cycle. After the third healing cycle, tensile strength and strain recoveries were maintained at 0.6 MPa and 272.5%, respectively. The microscopic images as shown in FIG. 3 depict the fresh cut and the thermally healed surface. A noticeable reduction in scar visibility and shrinkage of the scar was further observed post thermal treatment.

[0042]

[0043] With reference to FIG. 2, under the thermal condition, the restriction of ENR network chains diminishes, allowing oxygenous groups along the ENR chain (ENR-O ) to interact with Zn ²⁺ salt ions present on the CNF surface freely, after which the bonds between the ENR chain and Zn ²⁺ ion is reconstructed at room temperature. When the ENR chains are relaxed, the reversible ionic bonds between ENR chain and Zn ²⁺ heal upon cooling at room temperature, leading to self-healing of the article.

[0044] The self-healing assessment results are shown in FIG. 3 and in FIG. 4.

[0045] With reference to the experimental examples, it is observed that the recovery strength is increased to about 65% of its original value and about 90% of strain recovery was observed after the thermal treatment at 80 °C for 1 hour and subsequently at room temperature for 3 hours. The microscopic images as shown in FIG. 3 depict the fresh cut and the thermally healed surface. A noticeable reduction in scar visibility and shrinkage of the scar was further observed post thermal treatment.

[0046] For assessing the air leakage and referring to FIG. 4, the article was cut and the cut surfaces were contacted and thermally healed at 80 °C for 1 hour and relaxed at room temperature for 3 hours. Next, the air leakage test was conducted on the article before and after the self-healing process. With natural rubber (NR) glove used as a control sample in this test, it is observed that no air bubbles observed from the article prepared in accordance with the present invention when the air was purged, indicating that the cut surface had completely healed. On the other hand, air bubbles were released rapidly from the control sample, suggesting no self-healing mechanisms present in standard NR gloves.

[0047] It is envisaged the self-healing process can be repeated up to 3 times for the damage that has occurred in the same area.

[0048] With the method of the present invention, the cost of manufacturing can be significantly reduced. [0049] While the invention has been described as required in terms in preferred embodiments and specific operating ranges and conditions, those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.