CHEMICAL BONDING OF POLYMERIC AGGRAGATE PARTICLES AND/OR LIQUID WITH BITUMEN AND/OR BINDERS
The present invention relates to various methods of making polymeric aggregate particles-containing ionic functionalities and bitumen-containing ionic functionalities, based on using oxidising agents. The functionalised polymer particles and the functionalised bitumen or unmodified bitumen or binders can then be chemically bonded using a certain cross-linking agent. Also, The un-functionalised polymer particles and the functionalised bitumen or unmodified bitumen or binders can then be chemically bonded using a certain cross-linking agent. The final product is suitable for, for example, the surfaces for city streets, highways, airfields and other construction applications.
Polymers are chemical compounds built from large number of atoms. They are therefore of high molecular weight. Polymers can be of natural origin (e.g. cellulose, protein, natural rubber) or they may be synthetically produced {e.g. poly (ethylene), nylon, silicones}.
Bitumen is the residual material left after the fractional distillation of crude oil. It is a mixture of hydrocarbon compounds and other chemical complexes containing nitrogen, oxygen, sulphur, carbon-carbon double bonds and metals such as nickel and vanadium. Bitumen can be subdivided into three main fractions such as carbenes, asphaltenes and maltenes.
There is a large potential market for strong and successful chemically bonded polymers and bitumen and many companies have attempted to achieve this. However so far none have been very successful.
Failure generally seems to be due to:
• Formation of weak bonding between the polymers and bitumen. • The use of several stages and costly process.
Prior to the present invention, methods for bonding polymers and bitumen involved ; A) Exposing recycled plastic aggregates to ultraviolet irradiation in the presence of strong alkali. Which can be achieved as follows; i) Collect and sort out recycled plastic to facilitate cutting. ii) Wash recycled plastic by using a heated solution of caustic soda solution such as (sodium hydroxide) in water to remove any contaminants such as labels, grease, etc.
iii) Cut recycled plastic into small particles/strips approximately no more than 12mm wide and 25mm -100mm long. Then wash the strips again in a caustic solution and rinsed with water. iv) Mix the particles into a high concentration solution of aluminium hydroxide or calcium hydroxide. Use a tank for holding the alkali solution and an agitator in tank for stirring the solution and the plastic strips so the plastic strips are all thoroughly wetted and their surfaces are evenly exposed to ultraviolet light. Use an ultraviolet lamp with a substantially continuous wavelength spectrum in the rang of 290 nm to 380 urn. The ultraviolet light promotes a chemical reaction between alkali solution and the surface of plastics strips by etching the surfaces of the plastic strips and also alters the chemical make up of the surface of the plastic strips. The chemical reaction involves substituting hydrogen atoms in the plastic strips with cat ions from alkali solution. The exposure to ultraviolet light is for a short time( less than 24 hours) so that only surface portions of plastic strips are affected by this treatment. v) Remove the plastic strips from the solution, rinsed in water and dried, vi) Use plastic strips as aggregates to replace 10 to 100 percent of the rock aggregate suitable for use in bituminous mixtures. B) Upgrading plastic particles by coating them with a coating materials such as; ethylene- vinyl acetate resin, epoxy, urethane resin, acrylic resin, polyester resin or vinyl chloride resin. The adhesives may be mixed with solvent to modify its viscosity.
Coating the plastic particles with the coating materials can be achieved by rolling the plastic particles over the coating materials, spraying the coating over the particles or mixing the plastic particles in a container having the coating materials. Excess of the coating materials can be removed by use of a sieve. The size range of the plastic or rubber particles is between 2 to 20mm.
In this invention, the proposed solution to the weak bonding between the polymers and bitumen experienced in the mixtures produced using the above methods is generally via one of the following methods: 1. Oxidising the polymers and bitumen together and adding a cross-linking agent susequentley to the mix. 2. Oxidising the polymers and bitumen separately and then mixing them in the presence of a cross-linking agent. 3. Oxidising the polymers only and then mixing them with bitumen in the presence of a cross-linking agent. 4. Mixing the polymers and bitumen or binders in the presence of a cross- linking agent.
As part of the present invention, there is provided a method for modifying the surface of polymeric particles and bitumen, comprising the steps of:
(a) Treating the polymer aggregate particles and or strips with an oxidising solution such as chromic acid ( potassium dichromate, water and sulphuric acid) of the formula, (1) K2Cr2O7 + H2O + H2SO4
Or the effect of other oxidising solution ( potassium chlorochromate and sulphuric acid) of the formula, (2) KClO3 + H2SO4
Or the effect of other oxidising solution ( potassium permanganate and sulphuric acid) of the formula, (3) KMnO4 + H2SO4 (4) Or any other inorganic or organic oxidising agent. (5) (b) The treatment of a polymeric material and or a bitumen by an oxidising agent will introduce various ionic functional groups on the
surfaces. These functional groups can then be reacted further in presence of a cross-linker such as divalent compound ( e.g. calcium chloride) or polyelectrolyte polymer (e.g. a polybase such as polyethyleneimine) to form a chemical bonded between the polymer and the bitumen.
Example
(a). Functionalisation of polymers 1. Clean the recycle polymeric materials such as plastic or rubber to remove the labels and any other contaminants. 2. The clean polymeric materials are then cut into strips approximately 2 x 8cm or any desired size. 3. Mixing the clean strips of polymers or polymers liquid with an oxidising solution such as chromic acid comprising of potassium dichromate : Water : Sulphuric acid in a ratio such as 7 : 12 : 150 by weight. The reaction time from 2 minutes -24 hours. 4. The treated polymers from step 3 are then washed thougrouly with water to remove the un-reacted oxidising solution.
(b) Functionalisation of a bitumen and or binders A bitumen and or binders has been treated as described in steps 3 or using another oxidising agents such as sulphuric acid, hydrogen peroxides or acetic acids individually or collectively.
(C) Bonding the functionalised polymer with the functionalised bitumen or un modified bitumen and or binder. Mixing the ftmctionalised polymer and bitumen from step (a) and (b) with