Investigating the use of low and high-density polyethylene blends with waste material from three-layer factory tube for the third layer of shock tubes.

Polymeric shock tubes are now widely used in explosives systems for drilling and mining operations. Most shock tubes on the market consist of three layers of polymer, the first layer being Surlyn 8940 copolymer, the second layer Nucrel 31001 and the outer layer Borostar ME 6053 medium density polyethylene. Surlyn and Nucrel are usually sourced from DuPont, polyethylene from Charlotte Boralis. the main goal in this research is reducing the price of final shock tube and reuse the waste tube of plant (rejected shock tube) with improving the properties of product. For reaching to this goal, using polyethylene blend with available raw materials in the country and mixing them with rework from the shock tube production plant. For this purpose, different proportions of low- and high-Density polyethylene are blend using a twin-screw extruder and finally mixed with some of the factory's polymer rework. In the first phase, the low-density polyethylene LDPE 020, the high-density polyethylene HDPE HI 0500 and the filler calcium carbonate were blend in a twin-screw extruder and compounded with different percentages of 20/75/5, 30/65/5, 40/55/5 and 47/47/6 percent respectively. In the second phase, the resulting blend was mixed physically with 5, 10 and 15 percent three-layer tube rework (which was crushed with a crusher or pelletizer). The results showed that the 47/47/6 percent mixture had the best composition in terms of the production process, the properties of blend in terms of tensile strength (17/3 MPa), elongation percentage (458%) was suitable. In order to reduce the waste and cost of the product, the best processing results, product properties and costs are obtained when the above composition is mixed with crushed shock tube rework in a ratio of 90/10 (blend/rework). Tensile strength at break was 20/01 MPa and elongation at break was 478%. After evaluating the raw materials and accepting the results, the polymer blends were used on an industrial scale to produce shock tubes. The performance of the resulting shock tubes was then compared using various tests, including mechanical tests, oil penetration resistance, thermal shrinkage (in 60°C: upper 7% and in 80°C: upper 9%), burst strength, thermal aging (before aging:170 N, after aging: N₅, N₆, N₇, N₈: upper 170 N), and explosion velocity (upper 1890 m/s). The results showed that by using the polymer blend with rework, the mechanical properties of the shock tubes produced met the standard (tensile strength of more than 170 N/m² and elongation percentage of more than 220). The results of the oil penetration resistance (45-50 h), burst strength and aging tests also showed that all shock tubes manufactured with the new third layer had acceptable properties and were on the same level as shock tubes made of Boralis polyethylene.