WO2016072830A1

WO2016072830A1 - A process for introducing filler nanoparticles into a polymer to form a nanocomposite

Info

Publication number: WO2016072830A1
Application number: PCT/MY2015/000066
Authority: WO
Inventors: Kim Song TAN
Original assignee: Lembaga Getah Malaysia
Priority date: 2014-11-07
Filing date: 2015-08-11
Publication date: 2016-05-12
Also published as: MY173273A

Abstract

The present invention relates to a process of introducing filler nanoparticles into a polymer to form a nanocomposite, the process comprising synthesis of nanoparticles in-situ of aqueous polymer by nucleation and growth of nanoparticles from a precursor solution under the hydrothermal conditions without destabilizing the polymer, wherein the filler nanoparticles are metal-oxide nanoparticles and polymer is rubber latex.

Description

A PROCESS FOR INTRODUCING FILLER NANOPARTICLES INTO A POLYMER TO FORM A

NANOCOMPOSITE

FIELD OF INVENTION The present invention generally relates to a process for introducing filler nanoparticles into a polymer to form a nanocomposite.

BACKGROUND OF INVENTION

Nanocomposite materials are comprised of two or more materials, with at least one of the materials including particles having no dimension greater than several hundred nanometers (nm). Polymer- based nanocomposite materials include a filler material of nanoparticles dispersed in the matrix of the polymer material. These materials have garnered interest in many technical fields requiring materials for optical, electronic, structural, and barrier applications because of the potential to combine certain material characteristics of the polymer with those of the filler material. While polymer-based nanocomposite materials are promising, there are shortcomings in known nanocomposite materials and their methods of manufacture. In order to achieve certain material characteristics and uniformity of these characteristics, it is beneficial for the nanoparticles to be homogeneously dispersed within the other polymer material of the nanocomposite.

Achieving a better filler particle distribution could well mean better mechanical, dynamic and thermal aging properties of rubber compounds or products. There are many types of fillers found in the rubber industry. Carbon black, being highly chemically compatible with natural rubber, is widely used if the color of the final products such as tires and engineering mounts is less imperative. Otherwise, other non-black fillers are employed. There is a trend of colored products over the traditional white and black versions due to changes in lifestyles. The most common non- black fillers are clays, silicas, silicates and calcium carbonates. These non-black fillers are available in powder form and the application of these fillers into rubber is not straightforward due to the nature of their surface chemistry, which are generally more polar and hydrated than carbon black. This makes them more difficult to interact with the non-polar rubber phase resulting in poor filler particle distribution and phase separation.

Mixing these materials in rubber requires modification to the surface chemistry and that includes coating the surface with compatible materials such as silane (SiH4), which is commonly found on clay particles. Surface modified filler undergoes conventional mixing methods, namely internal mixer, two roll mill or screw extruder. High energy is required to operate such mixing machines because of the increase in toughness due to the presence of filler. However, despite high energy consumption the distribution of filler particles can be poor. With current high energy cost alternative mixing methods are being researched.

One of the promising methods is to mix the ingredients in latex stage that requires minimum energy consumption. In situ polymerization in the presence of filler particles is a convincing method, but only for synthetic rubber where the process begins with monomers. Polymerization process can be performed in the existence of filler particles and this process has an advantage of forming macromolecules surrounding the filler particles to prevent physical contact between particles.

Natural rubber, on the other hand, is naturally high molecular weight polymer with giant chains encapsulated in latex particles. These latex particles are suspended in aqueous medium and the stability is achieved through adding ammonia or surfactants. Filler particles can be coexisting with latex particles in the suspension and the distribution of both entities can be easily achieved by pre dispersing the filler using a high speed mixer, ball mill or agitator bead mill. In the process of latex coagulation the filler particles are trapped and a composite material with an even distribution of filler can be obtained. Although relatively simple in preparation as compared to dry rubber processing, the latex route is a two-step process and in the first step, the filler's tendency to agglomerate must first be tackled before it is added into latex. The process of de-agglomeration can be time consuming and involves additional energy.

This patent application describes a completely new method to add filler particles into rubber. It is similar to the latex route described earlier, but the difference is obvious in the addition of filler. Firstly, there is no physical occurrence of filler particles in latex and high energy mixing process is omitted. Secondly, the process of creating the filler, by a process generally described as nucleation and growth in latex is novel and has not been reported elsewhere.

SUMMARY OF THE INVENTION

Therefore, the present invention provides a process of introducing filler nanoparticles into a polymer to form a nanocomposite, the process comprising synthesis of nanoparticles in-situ of aqueous polymer by nucleation and growth of nanoparticles from a precursor solution under the hydrothermal conditions without destabilizing the polymer, wherein the filler nanoparticles are metal-oxide nanoparticles and polymer is rubber latex.

In another embodiment of the present invention, the present invention provides a process which results in the synthesis of metal-oxide nanoparticles such as titanium dioxide (TiC ) from the precursor solution. The precursor solution may be selected from titanium tetraisopropoxide (TTIP) being stabilized by tetramethylammonium hydroxide (TMAOH).

In another embodiment of the present invention, the present invention provides a process which eliminates or reduces the need for subsequent addition of filler particles in dry rubber compounding. In another embodiment of the present invention, the present invention provides a process which provides better and homogeneous filler particle distribution as compared to the conventional mixing methods such as an internal mixer or a two-roll mill.

In another embodiment of the present invention, the present invention provides a process which works with guayule latex and synthetic latex.

The present invention consists of several novel features and a combination of parts hereinafter fully described and illustrated in the accompanying description, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWING

To further clarify various aspects of embodiments of the present invention, a more particular description will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawing. The invention is described and explained with additional specificity and detail through the accompanying drawing, in which:

FIG.l is a schematic diagram showing the concept for the process involved in the preparation of nanoparticles in the presence of latex particles.

DETAILED DESCRIPTION OF THE INVENTION

Generally, the present invention describes the incorporation of metal oxide nanoparticles i.e. titanium dioxide (Ti0₂) in natural rubber latex particles. It basically discloses the synthesis of Ti0₂ nanoparticles of anatase phase, wherein titanium tetraisopropoxide (TTIP) solution as a precursor is stabilised by tetramethylammonium hydroxide (TMAOH) in the presence of natural rubber latex via hydrothermal reaction. The process of nucleation and growth initiates particle formation in-situ of aqueous medium of the latex, to achieve homogeneous distribution of particles throughout the latex dispersion. The homogeneity of particles ascertains certain material characteristics and uniformity, thus improved properties of rubber compounds or products.

The present invention relates to a route to introduce filler particles in rubber. Hereinafter, this specification will describe the present invention according to the preferred embodiments of the present invention. However, it is to be understood that limiting the description of the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications and equivalents without departing from the scope of the appended claims.

More particularly, the present invention discloses the addition of filler particles in rubber via fabrication of nanoparticles in natural rubber latex using a precursor of filler, titanium tetraisopropoxide (TTIP), which is in the solution form and stabilized by tetramethylammonium hydroxide (TMAOH), through a process of nucleation and growth to initiate particle formation in- situ of aqueous medium of the latex, to achieve homogeneous distribution of particles throughout the latex dispersion. The latex referred to being natural rubber latex, whether a field, concentrate, modified or in compounds and final products prepared from latex.

The concept of fabricating nanoparticles from precursor in situ of latex is proven feasible by reference to morphological studies involving Field Emission Scanning Electron Microscope (FESEM] and Transmission Electron Microscope (TEM) where filler particle attachment to natural rubber latex particles was visually confirmed.

The precursor solution must be stabilized using bulky quaternary salt to prevent premature hydrolysis which can lead to irreversible reaction, forming titanium oxide with uncontrollable size and shape. The mixture of TTIP and TMAOH should be thoroughly agitated to ensure homogeneity prior to addition of distilled water that results in the immediate formation of a slightly cloudy colloidal suspension. The cloudy solution turns clear upon stirring at room temperature for 30 minutes.

The solution is then added to latex to make the final concentration of latex in the range of 5 - 50% drc. Thereafter, the mixed solution is placed under constant stirring at room temperature for another 30 minutes.

The final solution is transferred into a polytetrafluoroethylene (PTFE) lined stainless steel vessel and sealed before heating in an oven with temperature ranging from 100 - 180°C for 3 - 72 hours. After the desired time elapse, the content is removed and centrifuged to separate the solid and liquid phases. Being the lowest in density, latex particles accumulate at the top of the centrifuge tube whilst the highest density Ti0₂ particles and "heavy" latex particles pellet at the bottom of the tube. The "heavy" latex particles refer to modified latex particles containing Ti0₂. A clear serum should be obtained between the latex and Ti02. The centrifugation can be conducted in the range of 5000 to 15000 RPM. The time required for the centrifugation process varies with the speed chosen to ensure an effective separation. Water is then added into the separated phases and the process of centrifugation is repeated thrice.

Claims

1. A process of introducing filler nanoparticles into a polymer to form a nanocomposite, the process comprising synthesis of nanoparticles in-situ of aqueous polymer by nucleation and growth of nanoparticles from a precursor solution under the hydrothermal conditions without destabilizing the polymer, wherein the filler nanoparticles are metal-oxide nanoparticles and polymer is rubber latex.

2. The process as claimed in claim 1, wherein the process results in the synthesis of metal-oxide nanoparticles such as titanium dioxide (Ti02) from the precursor solution.

3. The process as claimed in claim 1, wherein the process eliminates or reduces the need for subsequent addition of filler particles in dry rubber compounding.

4. The process as claimed in claim 1, wherein the process provides better and homogeneous filler particle distribution as compared to the conventional mixing methods such as internal mixer or two-roll mill.

5. The process as claimed in claim 1, wherein the process works with guayule latex and synthetic latex.

6. The process as claimed in claim 2, wherein the precursor solution is titanium tetraisopropoxide (TTIP) being stabilized by tetramethylammonium hydroxide (TMAOH).