The effects of initiators mixture on suspension polymerization of vinyl chloride and its comparison with other productiv
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The effects of initiators mixture on suspension polymerization of vinyl chloride and its comparison with other productivity‑enhancing procedures R. Darvishi1 · Aref shahi2 Received: 5 September 2018 / Accepted: 31 October 2019 © Central Institute of Plastics Engineering & Technology 2019
Abstract Molecular and morphological properties of poly(vinyl chloride) (PVC) grains produced by suspension polymerization of VCM in the presence of a mixture of fast, mild and slow initiators (named as Cok process) was experimentally investigated in a pilot-scale reactor. In contrast to nonisothermal and fast initiator dosage process, using initiators mixture has the smallest influence on molecular weight and polydispersity index compared to the control process. It is found that Cok-PVC grains have the lowest cold plasticizer absorption and porosity among productivity-enhancing processes. Scanning electron microscopy showed that the particles produced by Cok process are more regularly shaped, with a smoother surface compared with the control resin. All three productivity-enhancing techniques lead to an apparent quality enhancement, higher flowability and greater bulk density of final grains when compared with control resin grains. While both nonisothermal and fast initiator dosage polymerization process broaden the particle size distribution (PID) of final PVC grains, applying Cok process produces particles with the same PID as a control process. In comparison with nonisothermal trajectory and continuous fast initiator dosage system, the Cok polymerization process leads to the most delay of motionless conversions, fusion time and the formation of a three-dimensional skeleton of primary particles as well. Keywords VCM suspension polymerization · Initiator mixtures · Molecular characteristics · Morphological properties
* R. Darvishi [email protected] 1
Polymer Engineering Department, Faculty of Petroleum and Gas (Gachsaran), Yasouj University, Gachsaran 75813‑56001, Iran
2
Department of Chemical Engineering, Petroleum University of Technology, Abadan, Iran
13
Vol.:(0123456789)
International Journal of Plastics Technology
Introduction Vinyl chloride monomer suspension polymerization is performed in a batch-wise process. As, the productivity of this high demand product is still low, improving the productivity of the batch polymerization process has been always considered as a challenging issue [1–5]. The enhanced productivity in VCM suspension polymerization process can be effectively achieved by reducing the batch time so that predefined specifications of the final product do not change remarkably. The polymerization of vinyl chloride monomer (VCM) is conventionally carried out isothermally in commercially producing plants. The cooling system of the reactors must be designed in such a way that it is able to remove the heat developed at the exothermic peak (Fig. 1). The typical trend of heat removal rate versus reaction time in vinyl chloride polymerization indicates the full capacity of the cooling system remains
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