Cai-Liang Zhang

Crystallization behavior of functional polypropylene grafted graphene oxide nanocomposite

With an aim to understand the role of polymer grafted graphene oxide (GO) in crystallization processes, a functional polypropylene (PP) grafted GO nanocomposite, prepared by isocyanate group-contained polypropylene (PP-g-TMI) reacting with hydroxyl and carboxyl groups on GO, was investigated in terms of isothermal and non-isothermal crystallization by differential scanning calorimetry. Comparing with the PP-g-TMI/natural graphite (NG) nanocomposite, a fully exfoliated and uniformly dispersed GO in the PP-g-TMI matrix for the PP-g-TMI/GO nanocomposite was affirmed by transmission electron microscopy and a large enhancement of its storage modulus. For isothermal crystallization at 140 °C, the addition of GO into PP-g-TMI accelerates the crystallization rate dramatically more than that of NG, indicating the grafted GO can act as a very efficient heterogeneous nucleation agent to increase nucleation dramatically. However, for isothermal crystallization at 126 °C, the crystallization rate of PP-g-TMI accelerated by grafted GO is inferior to that by NG, which can deduce that the grafted GO can restrict migration and diffusion of polymer molecular chains to the surface of the nucleus for spherulitic growth due to strong covalent binding with PP-g-TMI, the formed highly viscous and dense GO layers. These two converse effects of the grafted GO on crystallization can also explain the interesting non-isothermal crystallization behavior that the grafted GO increases the crystallization rate of PP-g-TMI at a low cooling rate, while it decreases the crystallization rate at a high cooling rate.

Concept of reactive compatibilizer-tracer for discovering interfacial reaction and morphology development for in-situ compatibilizing blending processes

Reactive blending, called also as in-situ compatibilization or reactive compatibilization, involving interfacial reactions leading to the in-situ formation of graft or block copolymer as compatibizers is an efficient route to create new materials that combines the desirable properties of each blend composition. It is very challenging to investigate a reactive blending process because both mixing and interfacial reactions between reactive polymers are highly coupled. Most importantly, the amount of the in-situ formed copolymer is often so low that it is very difficult to determine it in a relatively accurate manner. For this reason, a new concept called reactive compatibilizer-tracer, which bears reactive groups capable of reacting with its counterpart upon forming a copolymer for in-situ compatibilization of a reactive polymer blend and at the same time fluorescent labels allowing determining very small amounts of the in-situ formed compatibilizer was developed in this work. A copolymer of styrene (St) an...

Reactive compatibilizer-tracer: A powerful tool for designing, scaling up and optimizing reactive blending processes

A concept of reactive compatibilizer-tracer is developed to study reactive polymer blending processes in a twin screw extruder. It is summarized as follows. Fluorescent moieties such as anthracene are attached to a reactive compatibilizer so that the latter can be served both as a compatibilizer and a tracer. When evaluating its compatibilizing efficiency for a polymer blending system, unlike the polymer components of the blend which are continuously fed to the extruder, the reactive compatibilizer-tracer is added as a pulse. The concentration of the reactive compatibilizer-tracer in the polymer blend at the die exit is measured, in-line and in real time, using probes capable of detecting the signal of the emission of fluorescent moieties of the reactive compatibilizer-tracer. In the meantime, the corresponding size of the dispersed phase domains of the blend is determined off-line. These two pieces of information allow assessing the compatibilizing efficiency of a reactive compatibilizer in a much easier manner and using a much smaller amount of compatibilizer. Consequently, the concept of reactive compatibilizer-tracer can help select most appropriate compatibilizers under real industrial polymer blending conditions as well as scaling up and/or optimizing them.