# Evaluation of Waste Express Bag as a Novel Bitumen Modifier
## 1 Introduction  
With the rapid development of China's e-commerce economy, online shopping has become an indispensable part of Chinese life. Inevitably, a large amount of express waste will be produced. Express waste can be divided into three categories: express bags, cartons and tape. Among them, cartons can be recycled and reused very efficiently. About 50% of cartons can be reused in the US, and the number in Europe is 80% [1]. Express bags are sealed with sealing strips for transportation purposes. However, as the express bag is sealed, people have to tear open the bag in order to take out the goods. Therefore, waste express bags (WEBs) cannot be reused like normal plastic bags. In China,around 8.68 billion express bags were used in 2015 and this number has increased to 14.7 billion in 2016 [2; 3]. The huge number of WEBs can only be disposed of by landfill and incineration, which will cause serious environmental problems. Bitumen, as the most common paving materials in the world, can not only satisfy the basic function of road construction, but can also be used to deal with domestic garbage and industrial refuse. For example, some studies have used waste tire rubber [4] to modify bitumen, while some have used waste bottle plastic [5] or lignin [6]. Even waste cooking oil and waste glass can be used as modifiers [7; 8]. This garbage can also improve the performance of bitumen, for instance, the high temperature performance and fatigue resistance of the rubber modified bitumen is better than that of normal virgin bitumen [9]. From this perspective, using the WEBs as the modifier should also have some positive effect on the virgin bitumen. As a lightweight plastic bag, the main components of WEB are low-density polyethylene (LDPE), hot melt-adhesive, titanium dioxide ((TiO\({}_{2}\)), and calcium carbonate (CaCO\({}_{3}\))). Among them, the quality of PE accounts for about 85%, while the hot melt adhesive accounts for about 10%. The calcium carbonate and titanium dioxide, which are considered stain materials, account for about 5%. The hot melt adhesive mentioned here is a kind of pressure sensitive hot melt-adhesive, which is used as the sealing strip, the main component of which is polyolefin (PO). LDPE, which has a density of 0.915 g/cm\({}^{3}\) and a melting point of around 120-125 \({}^{\circ}\)C has been used as a modifier in previous research. [PERSON] et.al found that mixed LDPE with the SMA mixtures could enhance the performance of SMA at both high-temperature and low temperature environments. It was also found that LDPE improved the stiffness and modulus of rupture values of the asphalt mixtures at low temperature [10]. [PERSON] and [PERSON] tried to compare the EPS modified bitumen and PE modified bitumen [11] and used FTIR to indicate that there was no obvious change with the main functional groups in the waste PE modified bitumen. The result confirmed the modification mechanism of waste PE was physical process. [PERSON] and [PERSON] tried to mix waste PE and rubber to modify the asphalt matrix and study the properties of the modified bitumen [12]. In this study, the network structure of WPE formed by cross-linking action may be the reason for the improvement of its high-temperature performance. The paper also showed the combined modification of bitumen by WPE and the waste rubber powder had a better performance. Polyolefin, as the main component of the hot melt adhesive with the density of 0.91 g/cm\({}^{3}\) and melting point around 135 \({}^{\circ}\)C, has also been used to modify bitumen. [PERSON] used polyolefin to modify the bitumen and applied it in an ultrathin friction course [13]. [PERSON] studied the stabilization mechanisms in polyolefin-bitumen emulsions [14]. The WEB stain, with the main component as TiO\({}_{2}\), can also be used to modify the binder. The density of TiO\({}_{2}\) is 4.23 g/cm\({}^{3}\) while its melting point is over 1800 \({}^{\circ}\)C. It has been demonstrated that TiO\({}_{2}\) can absorb the nitrogen oxide in the environment by the catalysis of ultraviolet light.