Oxidized bitumen (bitumen is also referred to as asphalt) is used by the roofing industry to make roofing shingles and roofing membranes, among other things. Oxidized bitumen, also called “blown coating,” is generally produced by oxidizing a suitable feedstock bitumen, usually straight run bitumen or blends of straight run bitumen, by blowing an oxygen-containing gas (e.g., air, oxygen or an oxygen-inert gas mixture) through the bitumen feedstock at an elevated temperature (usually between 230° C.-290° C. (450° F.-550° F.)) for a certain amount of time (which can be more than 10 hours). Sometimes, this process is conducted in the presence of one or more catalysts. As a result of blowing oxygen, or oxygen-containing gas, through bitumen, the bitumen’s properties change. Generally, the blowing process is terminated once the bitumen has obtained the desired penetration, softening point and viscosity.
While the above described process is widely used in the industry, it has significant shortcomings. For example, the process is time consuming and the amount of energy needed for it to work is high because the process must be conducted at a temperature at which the feedstock is fluid enough to allow oxygen-containing gas to bubble through it. More importantly, the bitumen fumes produced by heating the feedstock and blowing an oxygen-containing gas through it are considered a health hazard and are potentially carcinogenic. Examples of compounds in these bitumen fumes include hydrogen sulfide, sulfur oxides (SOx), organosulfur compounds, hydrocarbons, nitrogen oxides (NOx) and carbon monoxides.
Prior to their release into the atmosphere, the bitumen 150/5 fumes created by the described blowing process are often passed through a water-sealed knockout tank and then subjected to an incineration process to reduce the emission of hazardous substances. However, these emission control measures are expensive and they usually do not prevent the emission of all potentially hazardous substances.
Roofing flux feedstocks require stringent properties to ensure that the resulting blown coating has properties meeting its specifications. Roofing flux feedstocks are in limited supply.
Thus, there remains a need to develop a method that does not rely on the described blowing process but that nevertheless results in bitumen compositions that have the properties of oxidized bitumen. The present invention addresses this need.
The present invention provides a non-blown roofing grade bitumen composition comprising: a) bitumen feedstock; b) polyolefin having a molecular weight of from about 800 to about 50,000 g/mol; and c) optionally one or more additives, wherein the softening point of the composition is above 70° C. as determined according to method ASTM D36 and the penetration of the composition is at least about 12 dmm at 25° C. as determined according to method ASTM D5.
In certain embodiments of the present invention, the bitumen feedstock is a paving grade bitumen. In other embodiments of the present invention, the polyolefin is selected from the group consisting of polyethylene (PE) homopolymer, low density polyethylene homopolymer (LDPE), linear low density polyethylene homopolymer (LLDPE), high density polyethylene homopolymer (HDPE), oxidized low density polyethylene homopolymer (Ox LDPE), oxidized high density polyethylene homopolymer (Ox HDPE), polypropylene (PP) homopolymer, ethylene-acrylic acid (EAA) co-polymer, ethylene-vinyl acetate (EVA) co-polymer, ethylene maleic anhydride (MAPE) co-polymer, propylene maleic anhydride (MAPP) co-polymer, Fischer-Tropsch wax (FT wax), and mixtures thereof. In other embodiments of the present invention, the additives are selected from the group consisting of plastomers, elastomers, waxes, polyphosphoric acid, flux oil, plasticizers and anti-oxidants. In other embodiments of the present invention, the polyolefin is present at a concentration of from about 0.5 weight % to about 25 weight % of the total weight of the bitumen composition; the asphalt feedstock is present at a concentration of from about 65 weight % to about 99 weight % of the total weight of the bitumen composition; and the one or more additives together are present at a concentration of from about 0.5 weight % to about 10 weight % of the total weight of the bitumen composition.
In certain embodiments of the present invention, the bitumen composition has a softening point at a temperature of from about 80° C. to about 115° C. as determined according to method ASTM D36. In other embodiments of the present invention, the bitumen composition does not comprise styrene/butadiene/styrene triblock copolymer (SBS). In other embodiments of the present invention, the bitumen composition is made by a process of mixing the bitumen feedstock with a polyolefin having a crystallinity of greater than 75%.
The present invention also provides a method of making any of the above bitumen compositions, comprising mixing the polyolefin or mixtures of different low molecular weight polyolefins with the bitumen feedstock at a temperature of from about 75° C. to about 200° C. for a time of about 30 minutes to about 6 hours. In other embodiments of the present invention, the mixing is done by using a low shear mixer at a speed of from about 5 RPM to about 100 RPM.
The present invention provides a non-blown roofing grade bitumen composition comprising: a) bitumen feedstock; b) polyolefin having a molecular weight of from about 800 to about 50,000 g/mol; and c) optionally one or more additives, wherein the softening point of the composition is between 57° C. and 113° C. as determined according to method ASTM D36 and the penetration of the composition is at least about 12 dmm at 25° C. as determined according to method ASTM D5.
In certain embodiments of the present invention, the softening point of the composition is between 57° C. and 66° C. as determined according to method ASTM D36 and the penetration of the composition is from about 18 to about 60 dmm at 25° C. as determined according to method ASTM D5. In other embodiments of the present invention, the softening point of the composition is between 70° C. and 80° C. as determined according to method ASTM D36 and the penetration of the composition is from about 18 to about 40 dmm at 25° C. as determined according to method ASTM D5. In other embodiments of the present invention, the softening point of the composition is between 85° C. and 96° C. as determined according to method ASTM D36 and the penetration of the composition is from about 15 to about 35 dmm at 25° C. as determined according to method ASTM D5. In even other embodiments of the present invention, the softening point of the composition is between 99° C. and 107° C. as determined according to method ASTM D36 and the penetration of the composition is from about 12 to about 25 dmm at 25° C. as determined according to method ASTM D5.
