The polymer butyl (IIR – isobutylene isoprene – rubber) is an elastomer with a small number of double bonds, produced through co-polymerisation of isobutylene and isoprene.
- With careful compounding Butyl has really good tensile strength.
- Butyl has very low permeability to air and other gases.
- Excellent resistance to ozone, oxidation and sunlight.
- Excellent temperature range of -45º C to +130º C for normal compounds and even better with special formulations like cured resin.
- Butyl has very low resilience which makes it ideal for vibration damping and shock absorption applications.
- Butyl has moderate resistance to abrasion and compression set.
- Resistance to chemicals; resistant to most inorganic products. Highly resistant to mineral acids, alkalines and aqueous acids. Not recommended to use in contact with oils, or hydrocarbon solvents.
The polymer EPDM, ethylene-propylene rubber, is produced through co-polymerisation of ethylene, propylene and diene monomer, producing a polymer made up of saturated linear macromolecules with a paraffinic structure.
In addition to the base polymer, both EPDM and Butyl contain reinforcing carbon black, fillers, process chemicals, antioxidants and vulcanising agents. After mixing the ingredients into a homogenous plastic compound, two layers of the rubber are rolled out in a calender to form a double sheet. Vulcanisation is then carried out. The long rubber molecules in the material are cross-linked through heat and pressure, creating an elastic membrane.
- Excellent inherent high and low temperature ranges. Typically -45º C to +120º C for standard compounds.
- Special compoundig can increase some grades to function continually at +140 º C.
- E.P’s are inherently resistant to attack by oxygen, U.V., Ozone and extreme weather environments, and will give long service in these contidions.
- E.P’s do not have good adhesion properties and expert advice should be sought from our Technical Department about bounding applications.
- Resistance to Chemicals; resistant to many chermicals and solvents. Good resistance to many corrosive chemicals. The performance of E.P’s in hot water and high pressure steam is better than in dry heat.
RUBBERS VS PLASTICS
Below we compare two common membrane materials – EPDM (a rubber) and PVC (a plastic). Note that Southland Liners exclusively fabricates liners using rubbers such as EPDM and Butyl. We do not fabricate plastics. Here’s the reasons why:
Durability and UV resistance
EPDM is a synthetic rubber material that is stable and elastic, designed for decades of outdoor exposure to the elements. It is inert to the effects of microorganisms when buried. The high carbon black content of 35-40 % guarantees UV weatherability beyond the normal life of most alternative membranes.
PVC contains plasticizers, normally phthalates such as DEHP and Di-butyl phthalates, for flexibility. The plasticizers will diffuse and evaporate from the membrane over time, depending on the compound quality of the PVC – but the process is always ongoing. When the plasticizer is consumed the membrane will revert, during a short time interval, to a brittle, hard product with poor mechanical properties and with a total loss of elongation. PVC is sensitive to heat, sunlight and microorganisms and is best used only for buried applications. Organic compounds in contact with PVC can result in microbiological degradation of the membrane and there is a risk of migration when in contact with other plastic materials and concrete.
Due to the loss of plasticizers PVC is also susceptible to weight loss and shrinkage over time.
EPDM is a fully elastic membrane with exceptional elongation properties for irregular surfaces. The membrane conforms to any irregularity and movements or settlements in the subgrade even after years of service.
Unreinforced PVC in thickness 0,50 – 1,00 mm is very susceptible to puncture due to rocks, sharp stones or rough substrates. PVC membranes rely heavily on protection via geotextiles or protective soil layers.
Interface friction angle
EPDM membranes with a textured surface have a typical friction angle of 24-27 degrees with most soil types. In the case of geomembranes excavations with steeper slopes are possible creating higher volume of storage on the same land surface.
PVC has a smooth surface with low surface friction. Typical interface friction angles are approx. 16-18 degrees with high risk of slippage of cover soils.
Low temperature environments
EPDM is not affected by low temperature extremes. The same is true for material exposed above the water level. It remains flexible and can be installed and joined at below freezing temperatures. It is resistant to temperatures as low -50° C.
PVC has a limited resistance to low temperatures. The membrane will become stiff and brittle, with increased susceptibility to tear and puncture. The highest quality PVC membranes have a brittle point of -25°C, but in most cases the effective low temperature resistance is restricted to -17° C.
Cost effectiveness and compatibility with Landscaping designs
EPDM panels are prefabricated, with custom sizes to fit exactly into the excavation of the reservoir. The flexible membrane can easily be transported and positioned on site, by small working crews. Installation of single panel projects for dams and ponds, up to 2000m² in size, can be performed by the owner.
PVC is also prefabricated to large panels with similar methods, but 0,75-1,00 mm PVC is not as durable and resistant to installation stress and must be handled with care. In addition protection from environmental degradation will require a minimum 50 cm of soil cover. EPDM can be installed exposed to the atmosphere and landscape rocks can be placed directly on the membrane.
The Environmental concern
EPDM membranes are environmentally friendly, chemically stable and contain no dangerous additives or plasticizers which could be released. EPDM is also recyclable. The elastomeric components can be ground and mixed into new EPDM rubber compounds.
The Green Building Council of Australia has established a Green Star environmental rating system for buildings in Australia. One of the many goals of this initiative is “To encourage and recognise the reduction in use of Poly Vinyl Chloride (PVC) products in Australian buildings”.
PVC is a chlorinated product containing UV stabilizers and plasticizers. In summary, PVC is not environmentally friendly:
- Chlor organic chemicals are generally toxic to the environment.
- These chemicals have been linked with “green-house” effects, damage to the ozone layer in the atmosphere. In addition they are carcinogenic, have caused poisoning by PCB and are not biodegradable. The production of PVC raw materials is environmentally questionable.
- PVC contains phthalates, plasticizers which are proven carcinogens. PVC can cause dioxin damage and some PVC membranes even contain heavy metals. They can also contain chlorinated aromatic hydrocarbons, which are known health hazards