Experts estimate that by 2065 international geomembranes usage may reach more than half of the earth’s surface. Geomembranes have shown excellent functionality in a variety of areas.

Geomembranes are relatively impermeable membranes made from polymers (including bitumen), classified by the production process, polyethylene geomembranes use the blow moulding method and the flat extrusion method, with the blow moulding method (tube film method) accounting for over 70% of total production, followed by the flat extrusion method; PVC geomembranes use the calendaring and lamination method. Let’s know more about them!

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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.


2 Definition and classification of extruded geomembranes

1) Definition of extruded geomembranes

Extruded geomembranes, also known as flat film extrusion geomembranes, are molten resin plasticized by an extruder, extruded from the head slit die opening as a molten sheet, calendared and cooled by a roller, traction, trimming, and then rolled into a geomembrane. Most thermoplastics can be extruded to produce geomembranes.

Extruded geomembranes and blown geomembranes are both commonly referred to as extruded geomembranes. However, the differences between them are significant, both in terms of process and processing equipment, and in terms of product properties. Extruded geomembranes offer better transparency, gloss, crystallinity, hardness, and dimensional accuracy than blown geomembranes. Blown geomembranes (mostly polyethylene) have the advantage of better longitudinal tensile strength and transverse tensile strength and can be easily changed by altering the width of the geomembrane by changing the blow to swell ratio.

2) Classification of extruded geomembranes

  • a. Very low density polyethylene (VLDPE) geomembranes;
  • b. Low density polyethylene (LDPE) geomembranes;
  • c. Linear low density polyethylene (LLDPE or MLLDPE) geomembranes;
  • d. Medium density polyethylene (MDPE) geomembranes:
  • e. High density polyethylene (HDPE) geomembranes;
  • f. Polybutylene (PB) geomembranes; g. Super soft Polypropylene (PP) geomembranes;
  • h. EVA (ethylene vinyl acetate copolymer) geomembranes;
  • i. Soft polyvinyl chloride (SPVC) geomembranes; j. Composite geomembranes.

According to the structure and apparent state of geomembrane classification:

  • a. smooth geomembrane;
  • b. single-sided plus brown geomembrane;
  • c. double-sided plus brown geomembrane;
  • d. reinforced geomembrane;
  • e. reflective geomembrane;
  • f. insulation geomembrane;
  • g. composite geomembrane.

3) Development of extruded geomembranes

Extrusion method geomembrane, from the packaging materials manufacturing industry, the flow method of plastic film processing methods. But the width and thickness of geomembranes for the cast plastic film several times, dozens of times. For a long time, the development of wide extruded geomembranes has lagged behind that of blown geomembranes due to the difficulty of designing and manufacturing machine heads. The width of extruded plastic sheets in Italy in the early 1990s was only 3000 mm. By the mid-1990s, the width of extruded geomembranes had reached 5800 mm in Germany and 10000 mm in the U.S. China uses the extrusion method to manufacture geomembranes. It started in the early 1990s. Since entering the 21st century, the width of domestic extruded geomembranes has reached 8500 mm, with 6000 mm width being the dominant factor.

4) Current status and trends in extruded geomembranes

Extruded geomembranes can produce polyethylene (PE) geomembranes for engineering applications and soft polyvinyl chloride (SPVC) geomembranes with a narrow width of 2000 mm. The production process of polyethylene geomembranes is based on the blow moulding method, supplemented by the extrusion method (flat film extrusion). Blow moulding accounts for over 80% of total production, followed by flat extrusion. Extruded polyethylene geomembranes are mainly used to produce low density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and ethylene vinyl acetate copolymer (EVA) geomembranes for tunnel waterproofing.

Extruded geomembranes can be used to produce glossy geomembranes, single-sided or double-sided geomembranes with roughness, as well as composite geomembranes with geotextiles and geomembranes, such as one fabric, one film, two films and three films, etc. Geotextiles mostly use non-woven geotextiles.

The development trend of extrusion method geomembrane: geomembrane thickness to bipolar development, can produce thickness 0.2mm below the film and 2.0mm above the light film; for the production of composite geomembrane not suitable for composite geotextiles with thermal compounding method; for the production of thermoplastic polyolefin geomembrane not suitable for blow moulding geomembrane; for membrane shell continuous, membrane network composite structure and other new products to prevent row one functional product development and production.