PLASTICIZERS IN RUBBERCOMPOUNDS

Luis Tormento

October/2017

Introduction

• Plasticizers have the function of plasticizing the rubber compound, improving its processing, reducing the energy required for processing and assisting in the incorporation of the ingredients, improving their dispersion. In vulcanizates they reduce hardness and stiffness, increase elongation at break and improve their flexibility at low temperature. These changes are accompanied by a reduction in mechanical properties and elastic properties. Plasticizers are often used in order to reduce the viscosity of the compound, thus allowing additional fillers to be added; when used for this purpose, are called extensors.

Introduction

• In addition to plasticizers and extenders there are other products which do not modify the viscosity of the compound nor the properties of the vulcanizatesbut facilitate the processing of the compounds and are called process aids, which are generally combinations of waxes, fatty acid salts and other products composition not disclosed; are used on the order of 1-3 phr.

• In some rubber devices where there is a need to increase the tackiness of the compounds, we employ the so-called tackifiers in the order of 2-5 phr.

Plastizicers

• The most popular plasticizers are mineral oils, derived from heavy oil fractions. By their chemical composition they are classified as aromatic, naphthenic and paraffinic. Oils are complex mixtures of hydrocarbons, which are often mixtures of aromatic, naphthenic (cycloparaffin) and paraffinic structures. The character of the oil is determined by the viscosity-density constant, VGC (Viscosity Gravity Constant), which is given by the following empirical formula:

•

10G – 1,072 log(V-38)VGC = -------------------------------

10 – log(V-38)• G being the specific weight of the oil at 15.5 ° C and its Saybolt

viscosity at 38 ° C.

Plastizicers

• Another empirical feature that is frequently used is the aniline point defined as the temperature at which the miscibility between the oil and aniline occurs in equal volume. The more aromatic the oil, the lower its aniline point. Both constants are related by the formula:

• 647 - aniline point (° C)• VGC = --------------------------------------• 650• An important factor in choosing the type of plasticizer is

its compatibility with rubber. The following table shows some oils and their compatibility with some rubbers:

PlasticizersMineral oil type NR SBR BR NBR CR CSM EPDM IIR

Paraffin + + + - - - + +

Relatively naphtenic + + + - - - + +

Naphtenic + + + O O O + O

Relativelly aromatic + + + O + + + -

Aromatic + + + + + + O -

Highly aromatic + + + + + + O -

+ Compatible O Moderated compatibility – Incompatible

Plasticizers

• The plasticizing effect of a mineral oil increases with its aromaticity, which also contributes to the dispersion of the reinforcing fillers. A drawback of these oils is that they are staining and may partially interfere with peroxidic activity.

• Paraffinic oils function more as process aids than plasticizers and do not affect staining. Its use is limited to EPM and IIR rubbers and clear compounds. Naphthenic oils occupy the intermediate position, and are used as plasticizers and as extenders. They confer good resistance to low temperature.

Plastificantes

• The second family of products of greater consumption in the rubber sector, mainly for polar synthetic rubbers, are synthetic type plasticizers. Among them we can mention the derivatives of phthalic, adipic and sebacicacid esters; the trichresil or diphenylcresylphosphates are used to improve the flame behavior.

Contact

LT Químicos

Av. Pedro Severino Jr., 366 Cjto 35

04310-060 – São Paulo – SP – Brasil

Luis Tormento

NPD Director

Luis.tormento@ltquimicos.com.br

Tel: +55 (11) 5581-0708