PVC particle morphology and impact on products


The PVC resin is converted into a molten state under he […]

The PVC resin is converted into a molten state under heat and shear during processing. This melt flow behavior is usually explained by molecular structural parameters such as molecular mass, molecular mass distribution, and branched structure. With the deepening of research and the accumulation of practical knowledge, people have discovered some phenomena that cannot be explained by molecular structure parameters. For example, at lower temperatures, the viscosity of the melt does not increase but decreases. This type of phenomenon has spurred further exploration of the morphology of PVC particles [1-2].
 1.PVC particle form
All commercial PVCs are synthesized by an addition reaction. During the polymerization, the initiator molecules decompose to form free radicals and form an active center together with the surrounding vinyl chloride monomer. The reaction continues until the chain terminates. Generally, commercial polyvinyl chloride resins are classified into three categories: suspension polyvinyl chloride (S-PVC), bulk polyvinyl chloride (M-PVC), and emulsion polyvinyl chloride (E-PVC). Their particle morphology is as follows:
1.1 Suspension Polyvinyl Chloride (S-PVC)
The S-PVC resin is a white powder having a particle size of 75 to 250 μm, and the outer skin of the particles is connected to the primary particles or agglomerates inside the particles, and is almost integrated. The distance between the primary particles or the agglomerates is extremely small, and the size of the agglomerates is 1.5 to 3 μm, which is formed by agglomerating more than a dozen circular primary particles having a particle diameter of 0.7 μm. The finer particles that make up the primary particles are domain domains with a particle size of about 230 nm, which is composed of 5 nm macromolecular aggregates. The resin particles are all composed of sub-particles, agglomerates and primary particles, but the particle size of the different sample particles and the degree of looseness inside the particles are different [3], which can be divided into compact type and loose type. The schematic diagram of the microstructure of the resin particles is shown in Fig. 1. Figure 2 shows a scanning electron micrograph of the fracture surface of S-PVC resin particles, which more clearly shows the particle structure state of S-PVC.