WO2015068123A1

WO2015068123A1 - A novel process of reducing extractable proteins from natural rubber latex dipped products

Info

Publication number: WO2015068123A1
Application number: PCT/IB2014/065845
Authority: WO
Inventors: Upul Nishantha RATNAYAKE; Walpolage SHANTHA; Matarage Derrick Senarath Ananda AMARASIRI; Udaka Kaushyal DE SILVA
Original assignee: University Of Moratuwa, Sri Lanka; Rubber Research Institute Of Sri Lanka
Priority date: 2013-11-08
Filing date: 2014-11-06
Publication date: 2015-05-14

Abstract

A method for reducing extractable proteins (soluble proteins) from natural rubber (NR) latex and NR latex dipped articles with free of protein allergy is disclosed. The method involves dispersing of 2:1 type phyllosilicate clay within the natural rubber latex. The most preferred type of phyllosilicate is montmorillonite clay. Uniform dispersion of montmorillonite clay into nanoscale clay platelets within NR latex causes to combine latex proteins with clay platelets and, as a result, migration of latex proteins onto the surface of latex dipped articles is significantly prevented. Leaching of dipped articles/films fabricated with the compounded NR latex containing montmorillonite clay further reduces the extractable proteins to a lower level.

Description

BACKGROUND OF THE INVENTION

Natural rubber (NR) latex extracted from Hevea brasiliensis is a colloidal aqueous suspension of rubber (cis-l,4-polyisoprene) particles coated with phospholipids and protein layers. In addition to the dispersed rubber particles in the serum, NR latex consists of organic and inorganic components such as proteins, sugars, enzymes, metal ions. Out of those non rubber constituents, latex proteins, which account about 2.5 % of the latex composition, play an important role in chemical stability of the latex and in mechanical properties of the products produced from the NR latex. However, some of these latex proteins are considered as potential latex allergens which would be a serious disadvantage for products made out of NR latex.

Allergic reactions to humans due to latex allergens (latex proteins) were known for several decades and those reactions can be simple irritant contact dermatitis to systematic allergic reactions. In general, NR latex extracted from the rubber tree is converted either into dry rubber or into liquid latex concentrate, known as centrifuged latex. Dry rubber, the main raw material for dry rubber based produces (tyres, tubes, horses, engineering components, etc.), contains very low level of extractable proteins (EP) since most of the extractable proteins are washed off during the production process of the dry rubber. As a result, allergic reactions are seldom reported by the use of dry rubber products. On the other hand, centrifuged latex contains a significant percentage of EP dispersed within the latex serum. Products made from centrifuged latex can cause allergic reactions as EP is likely to migrate to the surface of the latex products and contact with the skin of the user. Medical latex products such as examination and surgical gloves, catheters and diaphragms are reported as potential sources for allergic reactions. These reactions may cause due the direct contact of latex allergens with the skin of the user or inhalation of airborne latex allergens. Latex protein allergic reactions caused from latex products include skin irritation, delayed type hypersensitivity (Type IV allergic reactions) and immediate type hypersensitivity (Type I allergic reactions).

Several procedures/protocol and methods have been proposed to reduce or denature the latex proteins in the centrifuged latex/latex products. Most of the procedures (such as chlorination and leaching), which are post production processes, reduce the EP significantly but such processes impart negative impact on physical properties of the latex products. Enzyme treatment methods proposed to denature latex proteins are expensive processes and also fail significantly eliminate the allergenicity caused from the of natural rubber latex articles.

US Patent, 6,979,634 Bl describes a method to reduce latex allergenicity by incorporating starch into the NR latex. In this method, allergenicity is prevented by reducing the allergen activity of latex products by adding starch/modified starch into the NR latex.

US Patent, 5569,740 describes a process of making deproteinized natural rubber latex. This process produces films with no latex proteins and with excellent film properties.

US patent, 5777004, disclosed a method of treating NR latex with protease and peptidase enzymes thereby latex allergens are converted into non-allergenic to humans. This invention includes the treating of NR latex with at least one enzyme having protease activity and at least one enzyme with at least peptidase activity, resulting in polypeptides fragments and amino acids within the NR latex which are not allergenic. The present invention relates to the reduction of extractable proteins (latex allergens) by hindering the migration of latex proteins within the latex film and thereby preventing the latex allergenicity resulted by the latex products.

SUMMARY OF THE INVENTION

Accordingly, disclosed herein is a method to reduce the extractable proteins (EP) in natural rubber latex films by incorporating a low concentration of montmorillonite (MMT) clay into the compounded centrifuged latex and subsequent preparation of latex films. A dispersion of montmorillonite clay prepared with the aid of surfactants is mixed with the compounded latex. The MMT clay exfoliates into single clay platelets (individual clay layers) within the latex and subsequently latex proteins are bound with clay platelets, preventing migration to the surface of latex films. In addition to MMT clay, the compounded NR latex film comprises common compounding and vulcanization ingredients. This compounded latex formulation is suitable for making latex products, especially latex gloves with no/very low extractable proteins. An example relates to the preparation of NR latex films comprise, in addition to Na montmorillonite clay, other common compounding ingredients such as sulphur, ZnO, accelerators, potassium laureate, etc.

An another example, leaching of vulcanized NR latex films containing low concentration of MMT clay reduces the extractable protein level below 50 μg/g, the sensitivity level of the measured method

DETAILED DESCRIPTION OF THE IVENTION

The present invention relates to the production of EP free/less NR latex and thus making latex articles, especially latex gloves with no latex allergic reactions. Further, the invention includes, whilst reducing the extractable protein levels, improvement of physio- mechanical properties of the NR latex films.

The present invention includes following features;

Centrifuged NR latex comprising about 60 % dry rubber content (DRC), an aqueous dispersion of montmorillonite clay and other commonly used compounding and vulcanizing ingredients.

phr referred to herein is defined as parts per hundred of rubberExtractable protein referred herein is defined as water soluble (extractable) proteins extracted from NR latex films or NR latex/clay nanocomposites. Exfoliation referred to herein is the separation/delamination of layered phyllosilicates (clay) into individual layers with 1 nm thickness, commonly known as platelets. These platelets are homogeneously dispersed within the NR latex. The degree of exfoliation significantly affects the extractable protein content of the latex films.

Intercalation as referred to herein is diffusion of organic molecules/polymer molecules into the

Interlayer spacing of the phyllosilicate clay.

Surfactant as referred to herein is defined as a chemical that stabilizes the clay-water mixture by reducing the surface tension at the interface between clay and water. Phyllosilicate clay

Smectite type clay, which belongs to structural family of 2:1 layered silicates, in which octahedral alumino layer is sandwiched in between two tetrahedral silicate layers. Commonly used smectite type clay is montmorillonite, hectorite and saponite. In this invention Na montmorillonite (MMT) is used. EXAMPLE 1:

NR latex/clay (Na montmorillonite clay in this experiment) nanocomposite films were prepared by mixing compounded centrifuged latex with montmorillonite (MMT) clay. The MMT clay dispersion was prepared using a combination of anionic surfactants and the compounding ingredients were prepared as standard dispersions. The exact formulation of the nanocomposite films is shown in Table 1.

The N R latex nanocomposite vulcanizate films comprising different concentration of MMT clay were analysed for extractable protein content and mechanical properties. Extractable protein content of the nanocomposite films was measured according to the Modified Lowry Method (ASTM D5712).

ZDEC: zinc diethyldithiocarbamate

Extractable protein (EP) content of NR latex/MMT nanocomposite vulcanizate films was measured to evaluate the effect of MMT clay on soluble proteins in the latex films. Figure 1 illustrates the variation of EP content in the latex films when MMT clay loading level was increased up to 6 phr. Figure 1 clearly shows that addition of MMT clay into the NR latex reduces the total EP level of the nanocomposite material. The NR latex nanocomposite film filled with 1.5 phr of MMT clay drops the EP content to 158 μg/g from 467 μg/g of NR latex film with no clay), a decrease of 65 %. As the MMT clay loading level is increased to 3 phr., there is an unusual increase in the extractable protein content which gradually reduces as the MMT loading is further increased step wise up to 6 phr.

The aforementioned variation (as shown in Figure 1) of EP with the increase of MMT loading level could be explained due to the variation of effective surface are of clay platelets formed as a result of exfoliated and intercalated structure of MMT clay within the nanocomposite films. Latex proteins are bound to clay platelets through Ή' bonding and as a result hinder the migration of EP onto the surface of the latex nanocomposite films. In addition, alkyl ammonium ions formed by reacting ammonia present in the latex and polypeptide chains of proteins can replace the Na+ ions which are within the MMT clay gallery.

Table 2 shows the mechanical properties of the NR latex nanocomposite vulcanizate containing different loading levels of MMT clay

As shown in Table 2, tensile properties are increased gradually with the increase of MMT clay concentration. From this experiment, it clearly demonstrates that the addition of MMT clay reduces EP content whilst improving the mechanical properties of the N R latex films

EXAMPLE 2:

NR latex/clay nanocomposite films prepared with different concentration of MMT were leached with water for 2 minutes at 60 °C.

Table 3 shows the EP content of post leached of NR latex/MMT clay films. As clearly shown in Table 3, noticeable reduction of extractable protein content of the NR latex films filled with MMT clay is achieved with a simple leaching of the nanocomposite films. Extractable protein content of all the NR latex/MMT nanocomposite films is less than 100 μg/g and the films with 1.5 phr and 6 phr of MMT clay further reduce the EP content below to 50 μg/g.

Table 1: Compounding formulation for latex/montmorillonite nanocomposite films

Table 2: Mechanical properties of NR latex/montmorillonite nanocomposite

Mechanical Montmorillonite clay concentration, phr properties of the

nanocomposite

0 1 2 3 4 5 6

Tensile strength, 19.04 21.74 24.22 26.82 27.65 28.72 30.53

MPa

0.49 1.5 1.66 1.75 2.05 2.74 2.85

300 % Modulus,

0.87 2.54 3.18 3.28 3.84 4.76 5.51

MPa

30.8 38.58 42.82 45.88 49.03 51.83 56.07

500 % Modulus,

MPa

Tear strength,

kN/m Table 3: Extractable protein content of N R latex/MMT films after leaching of 10 minutes

MMT loading level Extractable protein

of the films V-g/g

phr

0 153.91

1 51.64

1.5 9.83

2 52.93

2.5 71.89

3 98.19

4 85.48

5 59.24

6 22.37

Claims

We claim:

1. A natural rubber latex compound comprising;

a) natural rubber,

b) homogeneous dispersion of 2:1 phyllosilicate clay,

c) a curing system,

d) compounding ingredients wherein the extractable Protein content is reduced to less than 200 μg/g in cured cast films or dipped latex articles.

2. The type of phyllosillicate clay in Claim 01 is selected from montomorillonite, hectorite, saponite or sepiolite.

3. The curing system in Claim 01 consists of;

a) curing agent;

b) vulcanization accelerator or vulcanization

accelerator system;

c) vulcanization activators.

The phylocyllicate clay in Claim 01 is in the range of 0.5 - 10 phr.

The natural rubber latex compound in Claim 01 further comprising inorganic materials such as CaC0₃, kaiolin clay or mixture of one of those. The Extractable Proteins in cured cast films or dipped articles in Claim 01 further reduced to less than 50

by leaching the articles.

The cured natural rubber latex films or natural rubber latex dipped articles in Claim 01 comprises of tensile strength in the range of 25 to 35 MPa and a tensile modules of 300% elongation in the range of 1.5 to 3 MPa measured by ISO 37:2005 (E).

A natural rubber latex compound in Claim 01 further comprises synthetic latex.