Investigating the effect of clay nanoparticles on the properties of cross-linked polyethylene

Master's Thesis of Polymer Industry Engineering

Abstract

Cross-linked polyethylene is one of the materials that is widely used in the field of insulation production in cables due to its good electrical properties and good electrical strength.

Today. One of the methods of optimizing the properties and changing the behavior of polymers is the use of filler particles with nanometer dimensions. Since nano particles have been proposed as fillers in composites, many researchers have investigated the effect of these particles on the properties of different materials and have obtained significant results. This is due to the very large surface area of ??these particles and the interaction they establish with the continuous phase in the composite.

The purpose of this research is to investigate the effect of modified nano clay with the brand name cloisite 30B on the polyethylene baking process and also the effect of these nanoparticles on the physical, mechanical and electrical properties of the cross-linked polyethylene composite. Also, in this research, an attempt has been made to place peroxide particles between clay plates, in addition to better dispersion of nanoparticles, the efficiency of creating transverse connections has also increased and led to the achievement of higher properties. For this purpose, certain amounts of clay nanoparticles were mixed with peroxide (DHBP) and antioxidant (Irganox 1010) and a sufficient amount of acetone using a magnetic stirrer and ultrasonic bath, and after the mixture was completely dried, it was used to prepare composites of 3, 6, and 9 percent by weight of nanoclay. After preparing the samples, tests such as rheology to check the baking behavior; DSC test was used to check the thermal behavior of samples such as melting temperature, crystallization temperature and crystallization percentage, TGA test to study thermal-degradation behavior, XRD test to determine the distance between clay plates, TEM test to check how the clay plates spread in the matrix, tensile test and DMTA to check the mechanical and dynamic properties and finally dielectric constant, loss factor and fracture strength tests were used to check the insulation properties of the samples. The results of the rheology test showed that placing peroxide molecules between the clay plates improved the baking process. Also, according to the investigations, the maximum improvement in the properties was achieved in the sample filled with 3% by weight of nano particles, and increasing the concentration of nano filler beyond this amount has caused a drop in many of the mentioned properties. With the invention of the steam engine in 1786, which was the beginning of the industrial revolution, the first serious step towards the use of energy was taken. Following that, in the 19th century, Europe was gripped by a strong thirst to find and harness all kinds of energy. Since then, the conversion of all types of energy to each other, and especially to electrical energy, which is the most useful energy known, has been continuously followed. So that public places, train stations and lighthouses near the coast were provided with electric lighting. In this era, the electric voltage was low and electricity was transmitted by ordinary wires. With the invention and completion of the electricity generator and the use of water energy and fossil fuels in steam engines, the field of using electric energy increased. Along with the developments in the field of alternating current a.c.  And the conversion of low voltages to high voltages was achieved, the program of electricity transmission to distant points was put on the agenda, electrical networks were created and expanded. It was in this process that the use of cable also started.

1-1       History of cable manufacturing in the world

In 1876, the idea of ??producing cable with rubber cover was implemented. At this stage, several strands of copper wire were twisted together and covered with a kind of natural rubber called guttapersha[1].

In the early years of the 1880s, cables were made that were insulated and covered with waterproof materials. After that, the use of other materials became common. Thus, it can be claimed that the cable industry has a history of nearly 130 years..

At that time, the cable manufacturing process was such that first an insulating material of plant origin was wrapped around the conductor, dried at a temperature of 130-140C, then saturated with oily materials, resin or wax, and finally coated with lead. In 1887, networks with higher voltage gave way, so that in 1898, the first 10 kV three-wire cable was made for a three-phase alternating current network.

Along with the complementary process of making the cable that continued continuously, in 1935, a Swiss expert named Borel [2] by placing two electrodes in oil and by placing different layers of Insulation papers between two electrodes measured the breakdown voltage of these materials and showed that by improving the manufacturing conditions, the quality of paper insulations increases and they can be used at higher voltages. With this development, the production of cables with higher voltage expanded day by day, and by using other materials such as polyvinyl chloride [3], polyethylene and ethylene propylene rubber [4], the scope of activity in the cable industry expanded and attracted large investments. 1-2 Electrical properties and physical and chemical properties of insulating materials Insulators are widely used in the manufacture of power generators, motors, transformers, arresters, capacitors, cables, pressure switches and other pressure equipment. According to the type of application and the environmental conditions in which the insulation is placed, in addition to its electrical properties, other physical and chemical properties are also very important. The characteristics of an insulator that must be investigated in different applications are:

mechanical behavior

thermal behavior

chemical parameters

electrical properties

Economic factors

1-2-1 Mechanical behavior of the insulation material

The strength of the insulation material is the main and basic requirement. For example, the material of the lining plate of the groove of electric machines must be hard enough to be able to bend against the inner surface of the expanded gap without breaking, and the edge of the gap must resist flaking, vibration, the chemical effect of the used polishing oil, and the absorption of moisture. The protrusion of the coil should have high resistance to wear and low friction coefficient

Abstract

Recently, advances in Science and technology, which is accompanied with high technological electronic devices, demand compact and robust electrical insulations, so lots of researches have been done to find a material with excellent dielectric properties. Crosslinked Polyethylene nano composites are such materials that can be used as insulators. It is due to their high resistance against electrical, mechanical and thermal stresses. Since nano particles have been introduced as filler, lots of researchers have studied their influences on the properties of different materials and they achieved interesting results. This could be due to the vast huge surface of nano particles and their interactions with polymeric matrix. However, since nano science is still a new science, most of its aspects are not yet thoroughly understood. The aim of this study is to investigate the effect of nano clay particles called closite 30B on curing process and physical, mechanical and electrical properties of crosslinked polyethylene nano composites. Also, in this study efforts have been done in order to increase the crosslinking efficiency in addition to better distribution of nano particles by placing peroxide into the galleries of clay particles which leads to achieve better mentioned properties. For this purpose, certain amount of clay nano particles were mixed with peroxide and antioxidant in the presence of acetone by the aid of mechanical stirrer in an ultrasonic bath. When the mixture was dried completely, it was used for preparation of nanocomposites having 3 wt%, 6 wt% and 9 wt% of nanoclay.