WO2015094131A1

WO2015094131A1 - Natural rubber latex preservative with zinc oxide nanostructures

Info

Publication number: WO2015094131A1
Application number: PCT/TH2013/000064
Authority: WO
Inventors: Wirach TAWEEPREDA
Original assignee: UNIVENTURES PUBLIC Co Ltd
Current assignee: UNIVENTURES PUBLIC Co Ltd
Priority date: 2013-12-20
Filing date: 2013-12-20
Publication date: 2015-06-25
Anticipated expiration: 2016-06-20

Abstract

The composition of water and additional ZnO, modified with urea and isothiazolone, in producing natural rubber latex significantly prolong the fresh latex storage as it can induce bacteria cell death, due to interactions between reactive oxygen species and proteins, DNA or the cell membrane caused moderate termite mortality.

Description

NATURAL RUBBER LATEX PRESERVATIVE WITH ZINC OXIDE

NANOSTRUCTURES

DESCRIPTION

Technical Field

The invention relates to an applying green activated zinc oxide (GZ) as latex preservative to against putrefaction and coagulation, to preserve natural rubber latex, and to rubber products so obtained.

Background Art

The latex is composed with rubber particles disperse in an aqueous medium. The rubber particles are stabilized with anionic charge from phospholipid layer combined with protein hydrolysis for natural rubber latex. An aqueous medium is composed with carbohydrate and quebrachitol which are essential for microbial growth. The fresh field natural rubber latex after tapping and collection is commonly infected microbials. The microbial grow with interaction, including fermentation, with non-rubber components of the latex result in various small acid molecules are formed, particularly volatile fatty acids (VFA). Then, spontaneous coagulation of fresh field natural rubber latex is occurred. Furthermore, microbial infection involving fermentation provokes putrefaction results in bad odours and decreasing of the pH if the latex is not preserved. Usually, the latex is stabilized with ammonia. Ammonia enables to increases the latex pH to a value of over 8.0 and increasing electrostatic repulsion between the rubber particles. Moreover, ammonia has been found to provide a strong bactericidal effect at a level of at least 0.35% w/w on total latex. However, ammonia is health hazards and equipment corrosive from highly irritate of ammonia. For fresh field natural rubber latex, the ammonia gas is converted to ammonia solution with concentration 15-18% w/w before adding to the latex since ammonia gas is very dangerous for transportation and applying thus high amount of ammonia solution for longer preservation effects on the latex quality especially the dry rubber content is decreased.

To overcome or reduce the bad point of the utilization of ammonia at high concentration, several secondary preservatives were developed. For example, formaldehyde, sodium sulphite, zine oxide (ZnO), and tetramethylene thiuram disulfide (TMTD) are used as latex bactericides wherein ammonia has been partly or completely substituted by alkaline media or by urea. Although several methods have already been developed for the short-term and long-term preservation of fresh field natural rubber latex, many of these methods still suffer from one or more disadvantages or drawbacks.

A 1:1 mixture of ZnO and TMTD has been used for a long time to represent promising alternative latex preservative, typically in an amount of 0.1% to 0.5% w/w on total latex but TMTD is sources of carcinogenic nitrosoamines and may create serious health hazards for people working with. Object of invention

One objective of the present invention is the provision of an alternative or an improved method for the preservation of natural rubber latex.

Disclosure of invention

Said and other objects have been realized by the present invention, described and claimed below.

During the search for alternative and improved methods for the preservation of fresh field natural rubber latex, the inventors surprisingly have found that the addition of a small amount of a particular mixture of ZnO modified with urea and isothiazolone, significantly prolong of the fresh latex storage.

ZnO has a wide area of application such as semiconducting material with photoluminescent and electric conductivity which has a band gap value of 3.37 eV and an excitation energy band of 60 meV at room temperature, catalysis, and varistors. Chemical and structural properties of ZnO particles are very important in these applications. Nanostructure of ZnO has high levels of oxidative stress can induce bacteria cell death due to interactions between reactive oxygen species and proteins, DNA or the cell membrane caused moderate termite mortality.

An advantage of the method according to the invention is that the addition to fresh field natural rubber latex of ZnO self-assembly nanostructure based on urea at low temperature - possibly to combination with a further preservative - significantly increases the physic-chemical stability of the rubber latex and also increases the stabilization against putrefaction.

The invention is illustrated by the following examples without being limited thereto. 3

As indicated above, microbial infection of fresh field natural rubber latex results in the formation of acidic compounds, particularly VFA, and an increase of VFA's in the latex obviously indicates a decline in the colloidal stability of the latex dispersion. In order to evaluate the colloidal stability of rubber latex is defined as VFA number which is the number of grams of potassium hydroxide equivalent to the anions present as salts of steam-volatile acids in a quantity of latex with contains 100 g of total solids.

Table I: VFA number of preserved rubber latex

GZ* VFA number** of latex at storage time (days) % w/w 0 3 6 14

0 0.034 0.120 0.725 -

0.1 0.034 0.083 0.245 0.830

0.2 0.034 0.067 0.113 0.665

0.3 0.034 0.045 0.048 0.065

0.5 0.034 0.043 0.045 0.052

1.0 0.034 0.038 0.042 0.041

Natural rubber latex treated with 0.2% w/w ammonia

* GZ : TL® GZ (trade name of Thai-Lysatch, Thailand)

** VFA number testing according to ISO 506 procedure

Claims

A composition of formula (GZ) for preservation of natural rubber latex, comprising ZnO, Urea, Isothiazolone and Water.

A method for the preservation of natural rubber latex, characterised in that it comprises adding to natural rubber latex in total from 0.20% to 0.80% by dry weight as secondary preservative combined with ammonia at a concentration of 0.1% to 0.3% by weight on total latex.

Preserved rubber latex according to claim 2, characterised that it is in a non-concentrated form, having a rubber content of 20% to 40% by weight dry rubber on total latex.

Preserved rubber latex according to claim 2, characterised that it is in concentrated form, having a rubber content of 60 to 70% by weight dry rubber on total latex.