Abstract
High-density polyethylene (HDPE) is a major component of polyethylene waste, yet only under 29.9% of waste HDPE is recycled. As an important additive, polyethylene wax (PEW) is increasingly used in many industries such as plastics, dyes, and paints. The preparation of PEW has received considerable interest because recycling and precisely controllable production can bring huge economic benefits. In this study, to recycle waste HDPE, a single screw extruder was innovatively combined with a connecting pipe to prepare PEW from the pyrolysis of waste HDPE. Using a test platform, PEWs were prepared under different pyrolysis temperatures and screw speeds, and corresponding number-average molecular weights (NAMWs) of PEWs were measured. To precisely monitor NAMW of PEW, a program was developed in MATLAB. First, the relationship between NAMW and pyrolysis ratio was obtained, and a measure-point-independence verification was conducted. Then, modified Arrhenius equations and time-dependent pyrolysis temperature were for the first time introduced into the HDPE pyrolysis model. Furthermore, the screw-speed-dependent inverse method was proposed and validated for high-precision monitoring of NAMW of PEW from the pyrolysis of waste HDPE by extrusion. PEW of desired molecular weight was able to be precisely obtained from waste HDPE.
Highlights
Polyethylene (PE) materials have become more and more important to everyday life, being used in a wide scope of applications from pipe to packaging to fiber
polyethylene wax (PEW) was prepared from the pyrolysis of waste High-density polyethylene (HDPE) in a single screw
PEW was prepared from the pyrolysis of waste HDPE in a single screw temperature oxidizes or even spontaneously combusts
Summary
Polyethylene (PE) materials have become more and more important to everyday life, being used in a wide scope of applications from pipe to packaging to fiber. The properties of pyrolysis products can be affected for the reason that inhomogeneous heating can induce hot spots, excessive pyrolysis, and even carbon deposition of PEW In such cases, single screw extruder (SSE) is considered as a new and effective method to continuously prepare PEW with comparatively homogeneous heating [16]. A greater understanding of the mechanism of HDPE pyrolysis and a precise monitoring of molecular weight of PEW are needed to continue the development of this important technology. The complex reaction network often gives rise to a broad product spectrum [17] This complexity of the pyrolysis reactions makes it difficult to use experimental methods to obtain detailed mechanistic insight. The method of monitoring number-average molecular weight (NAMW) of PEW from available observations of pyrolysis temperature and screw speed is new.
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