Preparation of crosslinked polyethylene and organoclay nanocomposites by melt intercalation and optimization of the production process

Polyethylene polymers are widely used in the plastic World. This polymer group, which is formed more than 70% of the total polymer market, is easy useable, partly low-cost and easy to process.Polyethylene is a thermoplastic polymer which can be processed at a temperature between 150-200°C. Among materials with a maximum processing temperature of 75°C, polyethylene is one of the most preferred polymers. However, softening, flow and some other critical mechanical properties of polyethylene at high temperatures are adversely changing, and this variation restricts its more common application potential. For this reason, certain special applications, especially at high temperatures, have accelerated research on cross-linked polyethylene synthesis. Cross-linking can convert thermoplastic polymers into thermoset polymers, giving them superior properties such as higher thermal and mechanical strength. Various methods are used for the synthesis of cross-linked polymer structures. In addition to cross-linking with peroxide and radiation, one of the most important methods is cross-linking with silane grafting-water. In this study, it was aimed to synthesize LDPE-organoclay nanocomposites grafted by extrusion over radicalic reactions using silane compound, followed by preparation of cross-linked form by water boiling and optimization of process parameters. For this, the MMT clay sample with a 2: 1 layered structure was modified using CTAB to prepare the polyethylene / organoclay nanocomposites so that the polymer / clay interface energy would be reduced. Vinyltrimethoxy silane (VTMS), benzoyl peroxide (BPO) and organoclay ratios were selected as process parameters. In addition, the retention times of the prepared samples in boiling water for cross-linking were also investigated as another process parameter. The nanocomposite specimens prepared in this method are characterized by XRD, HRTEM, FTIR and DSC techniques. The FTIR and DSC analyzes revealed that the cross-linking density of cross-linked polyethylene increased with increasing VTMS ratio. Optimum VTMS, BPO and organoclay ratios were determined as 3.5%, 1.0% and 3.0%, respectively. In addition, Response surface methodology (RSM) was used to statistically optimize the process variables and to determine the mathematical relationship.Optimum values for BPO, VTMS, organoclay and boiling time for percent elongation were found to be 1.00, 2.00, 2.57 and 12.47 respectively (R2 : 0.9271).