Structure And Properties Of Recycled Polyolefins And Modified Asphalts In Reactive Extrusion Method

Using recycled polyolefins to modify asphalt can not only promotethe performance of asphalt material and decrease the cost of asphaltmodification but also develop an extensive application approach torecycle the waste polyolefin plastics. Aiming to take better advantage ofrecycled polyolefins, the structure and properties of typical recycledpolyolefins were investigated and four different kinds ofpolyolefin-modified asphalt were compared. Effects of virgin andrecycled polyolefin on the properties, microstructure and storage stabilityof modified asphalt were summarized. At last, polyolefin-modifiedasphalt with high storage stability was prepared with reactive extrusionmethod.First, structure and properties of typical recycled polyolefins werestudied. Fourier Transform Infrared Spectrometry (FTIR), DifferentialScanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA)were used to characterize the typical recycled high density polyethylene(RHDPE). Then rheological and mechanical properties were analyzed. The results indicate that the structure of HDPE changes obviously duringrecycling and using processes. The carbonyl group of RHDPE increasedas the degree of aging and recycling increased. The melt flow rate andmechanical properties deteriorated. The chain breaking and oxidationwere mainly observed during the aging, accompany by mechanicalperformance and melt flow rate deterioration.Second, virgin and recycled polyolefins modified asphalt werecompared. The classical properties of modified asphalt, includingsoftening point, needle penetration and ductility, were tested. Opticalmicroscope was used to characterize the distribution of polyolefinparticles in asphalt matrix. DSC was also used to study the thermalproperties. The results indicated that RHDPE-modified asphalt had highertemperature resistance and shorter ductility at15℃and shorter needlepenetration at25℃than HDPE-modified asphalt, while the recycledpolypropylene (RPP) is on the contrary. Compare of different kinds ofpolyolefin-modified asphalt illustrated that RHDPE-modified asphalt hasbetter performance in high temperature than RPP, while thecorresponding virgins are on the contrary. The distribution state of thepolyolefin did not change remarkably after recycling. The melting pointand the heating fusion of polyolefin in the asphalt are higher than the purepolyolefin.At last, the storage stability of recycled polyolefin-modified asphalt was studied. In consideration of the difficult obstacle of macroscopicseparation of polyolefin-modified asphalt, reactive extrusion was adoptedto prepare the high stable polyolefin-modified asphalt.Polyethylene/crumb tire rubber composite modifier (BER) was firstprepared and then dispersed into the asphalt matrix, obtainingBER-modified asphalt with high storage stability. This method can notonly combine the advantages of both polyethylene and crumb tire rubberbut also utilize the waste rubber resource, promoting the performance ofasphalt material and reducing the cost of modification. The classicalproperties, microstructure, storage stability, thermal properties,rheological properties of prepared BER-modified asphalt were analyzed.Extraction method combined with FTIR was used to investigate thestability mechanism. The results illustrated that compatibilizer contenthas little effect on the softening point, needle penetration and ductility ofthe BER-modified asphalt. With the content increasing, the storagestability was improved and BER particles dispersed in the asphalt matrixmore uniformly. What’s more, BER-modified asphalt with high storagestability was obtained when the ratio of HDPE and CTR was controlled in30/70. The strong force of extruder had positive effect on the stability ofmodified asphalt. After adding BER, the storage modulus and lossmodulus were obviously improved and loss tangent reduced. Comparedto pure HDPE, the melting point of HDPE in BER-modified asphalt was reduced, while heating fusion improved. Furthermore, the heating fusionincreased as compatibilizer content increasing. The characteristicabsorption peaks in FTIR indicated that the chemical interaction occurredbetween modifier and asphalt. Based on the experience results andanalysis, a new kind of stability mechanism model of BER-modifiedasphalt was proposed.