Choose the best materials to produce compactors (PVC, TPE or rubber)
Let’s compare thermoplastic elastomers and rubber to find out if thermoplastic elastomers (TPE) are more reliable and economically sound than rubber.
It’s important to realize that thermoplastic elastomers (TPE) and rubber – polymeric compounds.
There are two types of polymeric compounds used to produce sealing gaskets for windows and doors for plastic and aluminum constructions:
- Rubber – saniprene with different supplements;
- Thermoplastic elastomers (TPE).
Manufactures use two types of rubber to produce compactors:
- EPDM – (ethylenepropylene diene M-class rubber)
To simplify manufacturing method of EPDM vulcanization we introduce ethylene-propylene-diene monomer (ENB) in molecular chain, picture 1. Sulfur and synthetic vulcanizing compositions are parts of EPDM. Chemical cure produces cross-linkage of rubber macromolecules forming temporary network, picture 2. Cross-linkage provides rubber with recoverability after mechanical deformation (impulses, tensions).
High quality EPDM rubber for gasket production is imported to Russia from West European countries (Germany, Italy) and Asia (South Korea, Taiwan, Japan). That’s why the production of sealing gaskets made of EPDM rubber is expensive and noncompetitive. EPDM rubber used in Russia consists of 30% of rubber and 70% of economic loading (soot / black carbon) and softener (oil).
Know how to choose EPDM rubber
It leaves a black carbon line on the white list of paper. Laboratory environment only allows appraising EPDM rubber quality.
Rubber production is laborious and expensive process. The shape is made by special extrusion machine and vulcanization of derived product must be continuous. That’s why the price of products so high. Cheap rubber is fragile and short-lived, contains a little carbon. EPDM chemicals can’t be used with foodstuffs.
- Silicon rubber
Such rubber is obtained of organic substances, contains silicium (Si). Silicon rubber is more expensive than EPDM rubber. Rubber is time-proof, flexible in low temperature because of rubber structure, picture 3. Peroxide cure is used to produce silicon rubber. It’s more expensive than chemical cure. We use silicon rubber in highly tailored engineering fields in bad weather conditions. Usage of silicon rubber for windows, doors and aluminum constructions is beside the purpose.
Advantages of compactors made of EPDM rubber:
- high ozone and UV resistance level;
- strain stability;
- wide variety of operating conditions;
- keeps elasticity below -40 centigrade.
Disadvantages of compactors made of EPDM rubber:
- high price;
- production time;
- color products are more expensive than black ones;
- don’t weld when heated;
- mustn’t contact foodstuffs.
Polymer recycling industry grows rapidly. Low-tech rubber is changed for thermoplastic elastomers (TPE). Mature European and Asia markets show this tendency.
Types of thermoplastic elastomers:
- Polyvinylchlorid (PVC)
PVC appeared 200 years ago (picture 4), wasn’t used in production because of material waste. When heated PVC decays and educes chlorine hydride. UV-destruction is caused by the sun when heated.
PVC is rosin used to make plastic windows. It contains 40-60% of flexibilizers. Flexibilizers leave a product in operating time. The product becomes smaller in size and loses its functionality. Soft resin contains 10% of stabilizers – ammonium adipate that make it dangerous for the environment and short-lived.
PVC plastic compounds harden when cooled and may crack. PVC plastic compounds are the cheapest ones used to produce the cheapest rubber and they have a lot of disadvantages.
Blends of TPE are more popular among customers. Black rubber makes the material elastic like rubber and they can be easily recycled when heated because of small amount of plastic. Manufactures use two types of TPE to produce sealing gaskets:
- Dynamically vulcanized thermoplastic elastomers(TPE-V)
TPE-V consists of EPDM, plastic, softeners and fillers. It’s similar to EPDM rubber, but it offers thermoplastic properties (fluidity at processing temperatures) because of plastic. Mixture of composition in double spiral mixer allows vulcanizing rubber dynamically. Thus dynamically vulcanized thermoplastic elastomers have the same properties as EPDM rubber but they are a little bit less elastic because of plastic.
- Thermoplastic elastomers TPE-S (TPE based on SEBS)
TPE-S is one of the latest world developments. SEBS (styrole-ethylene-butylene-styrene block-copolymer, picture 5) is used instead of rubber.
The picture shows that SEBS is similar to EPDM, but it needs physical cure instead of chemical cure, picture 6.
Picture 6 is similar to picture 2, but cross-linkage differs. We can’t recycle rubber after vulcanization. SEBS changes its properties when heated more than processed compound.
Extrusion technique is used to recycle thermoplastic elastomers TPE-S (TPE based on SEBS). SEBS is stable to ozone and UV-destruction. SEBS differs from EPDM in that it doesn’t require any chemical additives for vulcanization. The material is ecologically friendly, may contact foodstuffs and may be used to produce patient care items.
Advantages of sealing gaskets made of TPE-S (TPE based on SEBS):
- low price;
- high ozone and UV resistance level;
- strain stability;
- wide variety of operating conditions (a wide variety of compactors, food containers, patient care items);
- keep elasticity below -40 centigrade;
- weld easily;
- production time, wasteless;
- price for color and black products is nearly the same.
The only disadvantage of TPE-S is that it’s a little bit less elastic than rubber.
Different types of materials to produce seals are in great demand on the market. The materials described meet the requirements ГОСТ 30778-2001: Sealing gaskets for windows and doors made of TPE. Engineering specifications.
Each material has its price. Sealing gaskets made of TPE-S (TPE based on SEBS) are becoming first nowadays by comparing price and quality.