How to Distinguish Synthetic Rubber and Plastics
- Updated on January 21, 2022
With the technical development of high molecular material many new polymeric materials not only have the high elasticity of traditional cross-link vulcanized rubber, but also have the characteristics of ordinary plastics easy to process. However, many new polymers are not easy to be categorized by its name into plastics or synthetic rubber.
“Those with elasticity are synthetic rubber and those without are plastics?”
“It’s not that simple!”
Now we find a way from the definition in Import and Export Tariff Rate of the People’s Republic of China ( “IETR” thereafter) to distinguish synthetic rubber and plastics.
Definition of Synthetic Rubber
The term “synthetic rubber” in Chapter 40 of IETR applies to the following:
Class 1 Unsaturated Synthetic Substance
It is referred to those that can be made irreversibly into non-thermoplastic by sulfur sulfide. This substance can be elongated at the temperature of 18 to 29 degrees C to 3 times of its original length without breaking. When it’s elongated to 2 times of the original length, within 5 minutes it can return to no more than 1.5 times of the original length. In order to carry out the above tests, the sulfide activator or promoter required for cross linking may be added, or the substance contained in points 2 and 3 of Chapter 40 Note V (ii), but not the substances required for non-crosslinking, such as increments, plasticizers and fillers.
Class 2 Polysulfur Rubber (TM)
Class 3
Class 3 plastic grafted natural rubber, de-polymerized natural rubber or mixture of unsaturated synthetic substances and saturated synthetic polymers. However, these products must also comply with the requirement for vulcanizing, stretching and recovering in Class 1.
First “vulcanize”, then “stretch”, but also “recover”? Sounds complicated! In fact, the key step of this “complex experiment” is: vulcanizing and stretching test.
This experiment can determine whether the product can be chemically cross-linked with sulfur, forming a three-dimensional network structure, which has a certain degree of elasticity and tensile strength. Thus it can be confirmed whether the product is unsaturated synthetic material. Of course, the polysulfur rubber can be directly regarded as synthetic rubber.
Plastics in Name of "Rubber"
In summary, the vulcanizing stretching experiment in accordance with Chapter 40 of the IETR is the key element for determining synthetic rubber. The plastics that do not meet the experimental requirements can be classified as Chapter 39 of IETR.
Let’s take a few examples.
“Silicone rubber” or “silica gel” is very common in our daily life: baby nipples, phone cases, table mats.
The real identity of the “silicon rubber” is kind of polymer called polysiloxane, the main chain of which consists of silicon atom and oxygen atom by turns. The silicon atom usually connects with two organic groups. This polymer is not an unsaturated synthetic substance and does not meet the requirements of the vulcanizing and stretching experiment. Therefore, it is not classified as synthetic rubber in chapter 40 of IETR.
Primary-shaped polysiloxane is classified as tax number 3910.0000, with an import duty rate of 6.5%, and its products are classified as the relevant tax number in Chapter 39 of the IETR according to different uses.
Tax number 3901.4010, 3901.9010 in the so-called “ethyl propylene rubber”, it is not real rubber either.
The true identity of “ethyl propylene rubber” is ethylene-propylene copolymer, referred to as EPM, commonly known as binary ethyl propylene rubber. This polymer is not unsaturated synthetic substance and does not meet the requirements of the vulcanizing stretching experiment.
The ethylene-propylene copolymer (ethyl propylene rubber) with a content of more than 5% of the propylene and the density of 0.94 is respectively classified into 3901.4010 (≤0.94) or 3901.9010 (>0.94), and the import tariff rate is 6.5%.
Synthetic Rubber
Real Synthetic Rubber – Ternary Ethyl Propylene Rubber
Ternary ethyl propylene rubber is a complex of ethylene, propylene and a small amount third monomer of non-conjugated diolefin, referred to as EPDM. Due to the introduction of non-conjugate diolefins, the polymer has unsaturated double bonds. This means, it can not only be tested by sulfur sulfide in accordance with the vulcanizing and stretching experiment, but also maintain the characteristics of binary ethyl propylene rubber. It is a widely used synthetic rubber.
The primary shape of the ternary ethyl propylene rubber is classified as tax number 4002.7010 and its import tariff rate is 7.5%. The products are classified as the relevant tax number in Chapter 40 of IETR according to the relevant features.
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