1 Definition and classification of blown geomembranes
1) Definition of blow moulded geomembranes
Blow moulding, also known as “blow moulding”, is one of the methods of forming thermoplastics. It is a method of blowing hollow products by means of fluid pressure to make the hot blanks or sheets closed in the mould. The extrusion blow moulding method is a method of blow moulding in the front end of an extruder, where the extruded molten billet is blown into a tubular film using compressed air and then folded and rolled into a double layer of flat film (or tube film) after cooling.
The blow moulding method is also known as the tube and film method. Blow moulded geomembranes can be defined as: the resin is melted and plasticised by an extruder, then extruded through a ring-shaped die to form a thin-walled tubular blank, which is blown, cooled, cut open and flattened to form a geomembrane (i.e. blow moulded geomembrane).
2) Classification of blown geomembranes
(A) Classification by main raw materials
a. Very low density polyethylene (VLDPE) geomembranes;
b. Low density polyethylene (LDPE) geomembranes;
c. Linear low density polyethylene (LLDPE) geomembranes;
d. Polybutylene (PB) geomembranes;
e. High (medium) density polyethylene (HDPE and MDPE) geomembranes;
f. Ethylene/vinyl acetate copolymer (EVA) geomembranes;
g. Composite geomembranes.
(B) Geomembrane structure and apparent state classification
a. Smooth geomembranes.
b. Rough geomembranes.
c. Insulating geomembranes;
d. Filled geomembranes
3) A brief history of the development of blown geomembrane manufacturing
The development of polymeric geomembranes has been accompanied by the development of engineering applications and the exact date of their application in engineering is difficult to verify. Around the late 1930s and early 1940s, PVC membranes were first used to impermeabilise swimming pools, and the US Bureau of Reclamation was the first to apply PVC membranes to channel impermeability in 1953. Polyethylene geomembranes were first used in Germany in 1960, leading to their use throughout Europe, and then to Africa, Australia and North America.
Compared with the world’s advanced countries, the application of geosynthetic materials in China was about ten years later. In the mid-1960s, China began to use plastic film for channel impermeability projects. Earlier projects include Henan People’s Victory Canal, Shaanxi People’s Yinwei Canal, Beijing Northeast Wang Irrigation District and several irrigation districts in Shanxi. Later, it was gradually extended to projects such as reservoirs, sluices and cisterns.
Compared with traditional waterproofing materials, geomembranes have the advantages of low permeability, good low temperature flexibility, strong adaptability to deformation, light weight, high strength, good overall connectivity and easy construction. Over the next 20 years, geomembranes will be the main demand area for water conservancy projects. With the advancement of technology, the field of application of geomembranes is expanding. In China, HDPE geomembranes have become the preferred impermeable material for large and medium-sized urban landfills and other large metal mine tailings ponds currently being designed and prepared for impermeable treatment, large oil reserves and high-speed railway construction.
4) Status and development trend of blown geomembranes
(A) The current situation of blown geomembranes
①Manufacturing equipment: more than a single layer, multi-layer co-extruded plane film or spray brown method brown mask equipment. The ammonia-filled method of spraying brown blowing machine set due to the complexity of the process, damage detection indicators and other factors tend to eliminate the trend, was replaced by the spraying brown method. Manufacturing process is generally used on the blowing blow molding method, production equipment has basically realized the localization.
②Main raw materials: the use of medium density polyethylene and linear low density polyethylene geomembrane special material, domestic quality geomembrane raw materials continue to emerge, such as Sinopec, Qilu Petrochemical production of raw materials in widespread use; in recent years, a lot of imported raw materials from Iran and other countries are also in a steady flow.
③Product categories: double glossy geomembranes and single and double rough geomembranes produced by spraying rough method; white, black, blue, black and green geomembranes, etc. can be produced.
④Product specifications: thickness 0.2~2.5mm, width 4000~10000mm.
⑤Product quality: industry standard “CJ/T 234-2006 high-density polyethylene geomembrane for landfill” “CJ/T 276-2008 linear low-density polyethylene geomembrane for landfill”, GRI international standard “GM 13-2012 high-density polyethylene geomembrane test method performance and test frequency” “GM 17-2012 linear low-density polyethylene geomembrane test method performance and test frequency” and other geomembrane product standards.
**Application of the city: water conservancy and hydropower engineering (rivers, reservoirs, pumped storage power stations, etc.), transportation engineering (high-speed rail sliding layer), environmental protection engineering (sewage treatment plants, landfills, tailings storage, hazardous waste landfills, petrochemical, livestock breeding pollution prevention), etc.
5) Development trend of geomembrane by blowing method
Since 2006, the production of geomembranes in China has been growing at an average annual rate of about 35%. With the rapid development of China’s economy, increasing infrastructure construction, building “China’s high-speed railway” business card and the implementation of the “One Belt, One Road” strategy, the demand for geomembranes is increasing and the market outlook is broad. The future development of geomembrane blowing method, manufacturing equipment to the development of wide and efficient intelligent manufacturing, low energy consumption, high output, automatic metering and feeding, online thickness measurement, automatic off-roll weighing and packaging, automatic yardage, data collection and storage cloud transmission; geomembrane products to the direction of quality and stability, production line process ability index, geomembrane thickness uniformity, mechanical indicators qualified and stable, durability indicators to improve; product development to The development of product development to the direction of functional, flame retardant geomembrane, conductive geomembrane, intelligent geomembrane, etc. to meet the requirements of high-end engineering design.