Testing and qualifiying resins: The main standards

testing-qualifying-resines-standards

Resins are used in a lot of formulations of Coatings, Inks, Paints, and dispersions of fillers, quartz, pigments that have functional application.

As a definition of resin:

A thick, sticky substance that is produced by   some trees and that becomes yellow and hard after it is collected, or any of various similar substances produced by a chemical process for use in industry:

Or

any of various solid or semisolid amorphous fusible flammable natural organic substances that are usually transparent or translucent and yellowish to brown, are formed especially in plant secretions, are soluble in organic solvents (such as ether) but not in water, are electrical nonconductors, and are used chiefly in varnishes, printing inks, plastics, and sizes and in medicine.

resin-definition

On industry, Natural resin are still used in some applications but synthetic resins are more common where manufacturers develop specific product for each particular technical demand.

Main use is as a carrier of different pigments and fillers and should be formulated under premise that compatibility with solvent and rest of raw materials than are on formula and the end uses of the mixing.

synthetic-resins

Main function of the resin is to be cured by evaporation of solvent, by reaction of two component (resin and catalyst) by energy process of curing (UV light or LED).

The most values to test in a resin are focused in its performance and physical properties as  original form before cured process and after it when all resin has been cured at final application.

Most popular liquid resin uses in Potting system are liquid rubber cured under room temperature, typical values that you can find on TDS:

Appearance:

Liquid resin comes in forms of different appearances commonly described as clear, transparent, translucent, or in different colours, as an example showed on table detailed below:

Appearance assessment is a simple and easy way to estimate the quality of the liquid resin. A change in color indicates a change in wavelength absorption of visible light by the resin. Hence, it could be important to assess the appearance of the resin to ensure the quality of the resin as the change can indicate contamination or impurities in the raw material, process variations caused by heating and oxidation, or degradation of products exposed to weathering over time. There is no existing standard test method specifically for liquid resin. However, visual tests have been established by comparing the sample to a known standard. Objective measurements can also be done with color spectrophotometers that give reliable data on a consistent basis. ASTM 1544 and ASTM 5386 provide some information about the standard method to assess the color of any liquid materials.

Gardner Colour Scale:

astm5386

The Gardner Colour scale as specified in ASTM D1544 is a single number colour scale for grading light transmitting Scale samples with colour characteristics ranging from light yellow to brownish red. It is widely used for oils, paint and chemicals, such as resins, varnishes, lacquers, drying oils, fatty acids, lecithin, sunflower oil, linseed oil. The scale is defined by the chromaticities of glass standards numbered from 1 for the lightest to 18 for the darkest.

ASTM 5386

The major objective of the visual platinum-cobalt (Pt-Co) method of colour measurement is to rate specific materials for yellowness. This yellowness is frequently the result of the undesirable tendency of liquid hydrocarbons to absorb blue light due to contamination in processing, storage or shipping.

Clear liquids can be rated for light absorbing yellowish or brownish contaminants, using scales that simulate the long-established visual-comparison method just cited. Where needed, dimensions of colour can be reported to identify any pinkness or greenness (one dimension), or greyness.

Viscosity:

The term Viscosity requires a separate study, detailed below the most common methods:

Brookfield Viscosity:

The operation of the Brookfield viscometer is based on the principle of rotational viscosimetry; It measures the viscosity by capturing the torque required to rotate at a constant speed a spindle immersed in the sample of fluid to be studied.

The torque is proportional to the viscous resistance on the submerged shaft, and consequently, to the viscosity of the fluid.

Brookfield viscometers are easy to install and versatile and do not require great operational knowledge.

Each viscometer is composed of the following elements:

  • Viscometer body, consisting of an electric motor and a reading dial.
  • Interchangeable Spindler: these spindlers are numbered from 1 to 7, with 1 being the thickest. They have, on their axis, a signal that indicates the level of immersion in the liquid.

The adjustment and calibration of these stems is carried out by the manufacturer himself. Other adjustments and subsequent checks may be carried out using Newtonian liquids of known viscosity.

  • Thermostatic bath, to keep the product to be tested at the test temperature.
  • Support, to allow to hold the device and move it in a vertical plane.
  • Vessels, between 90 and 92 mm in diameter and 116 to 160 mm high.

Choice of speed and stem:

The viscosity / spindler ratio will be chosen, depending on the value of the viscosity to be measured, the desired accuracy and the velocity gradient tested.

It is necessary to make the choice so that the reading on the dial is between 20 and 95% of the scale. For better accuracy, it is advisable to use the interval between 46 and 95%.

Calculations:

Brookfield RV viscosity, in cP, of the sample to be tested, is obtained according to the following expression:

Viscosity calculation

K being a coefficient that depends on the speed / rod ratio used and L the average value of the two readings given as valid.

Höppler Viscosity:

A Type C Ball Drop Höppler Viscometer measures the viscosity of transparent non-Newtonian fluids very accurately and can be used in the temperature range of -20 to 120 ° C.

The determinations with this viscometer are based on the measurement of the time it takes for a ball to travel between the two extreme marks indicated on the viscometer. A Höppler type viscometer can be seen in the attached figure.

The apparatus contains, as a fundamental element, a thick-walled glass tube that has two annular signals marked hoppler-viscosityin the vicinity of its ends and which in turn is inserted into another much wider tube intended to accommodate circulating water as a thermostatic medium. The assembly is arranged in a slightly inclined position on a support similar to that of a microscope and can be rotated 180 ° around an axis perpendicular to both tubes.

The Höppler viscometer is very accurate and is frequently used in the chemical industry (polymer solutions, solvents, inks) in the pharmaceutical industry (excipients, glycerin) and in the food industry (jellies, sugar solutions), as well as among the manufacturers of mineral oils.

Calculations:

The time it takes for the ball to travel between the two extreme marks of the viscometer will be measured several times and the results will be averaged. This value is multiplied by the factor of the ball used, which can be found in the equipment manual. The result gives the viscosity, expressed in mPa.sec, which is equivalent to cPs. Is given by

El tiempo que tarda la bola en recorrer el espacio entre las dos marcas extremas del viscosímetro, se medirá varias veces y se promediarán los resultados. Este valor se multiplica por el factor de la bola utilizada, que se encontrará en el manual del equipo. El resultado da la viscosidad, expresada en mPa.seg, que equivalen a cPs. viene dado por:

Viscosity calculation

Viscosity (Kpa.seg) = cP = T (Db-Ds) x K

Where:

  • T indicates the fall time, in seconds,
  • Db is the density of the ball,
  • Ds is the density of the sample solution prepared
  • K is the ball constant, taken from the viscometer manual

Hardeness (Shore A):

As a definition:

Shore Hardness is a measure of the resistance a material has to indentation. There are different Shore Hardness scales for measuring the hardness of different materials (soft rubbers, rigid plastics, and supersoft gels, for example). These scales were invented so that people can discuss these materials and have a common point of reference.

DIN ISO 7619-2:2012

A method for determining the indentation hardness of vulcanized or thermoplastic rubber by means of a pocket hardness meter calibrated in IRHD. The hardness of rubber, as measured by an IRHD pocket meter or a Shore durometer, is determined from the complex response of the rubber to an applied indentation. An IRHD pocket meteris a portable hand-held durometer calibrated to measure on the IRHD scale. The measurement will depend upon:

  1. The elastic modulus of the rubber
  2. The viscoelastic properties of the rubber
  3. The thickness of the test piece
  4. The geometry of the indentor
  5. The pressure exerted
  6. The rate of increase of pressure
  7. The interval after which the hardness is recorded

Because of these factors, it is inadvisable to relate results obtained using an IRHD pocket meter directly to Shore durometer hardness values, although correlations have been established for some individual rubbers and compounds.

Tensile Strength:

As a definition:

A measure of the ability of a material to withstand a longitudinal stress, expressed as the greatest stress that the material can stand without breaking

ASTM D412

Is the most common standard for determining the tensile properties of vulcanized (thermoset) rubber andthermoplastic elastomers. Compounds in this family are used to create a vast array of consumer goods such as tires, footballs, and rubber bands. This family also produces highly specialized materials, such as O-rings on space shuttles, which must perform reliably under extreme environmental conditions.

ASTM D412 measures the elasticity of a material while under tensile strain, as well as its behavior after testing when the material is no longer being stressed. ASTM D412 is conducted on a universal testing machine (also called a tensile testing machine) at a rate of 500 ± 50 mm/min until the specimen fails. Though ASTM D412 measures many different tensile properties, the following are the most common:

Tensile strength – the maximum tensile stress applied in stretching a specimen to rupture.

Tensile stress at a given elongation – the stress required to stretch the uniform cross-section of a test specimen to a given elongation.

Ultimate elongation – the elongation at which rupture occurs in the application of continued tensile stress.

Tensile set – the extension remaining after a specimen has been stretched and allowed to retract in a specified manner, expressed as a percentage of the original length.

Elongation at Break %

As a definition:

Elongation at break is the percentage increase in length that a material will achieve before breaking. A higherpercentage usually indicates a better quality material when combined with a good Tensile Strength.

Solid Rubber that exhibits a high Elongation at Break but a low Tensile Strength may be indicative of a poorly mixed or under cured polymer, which if used to produce Rubber Gaskets or Seals will see premature failure.

References

    1. https://dictionary.cambridge.org/dictionary/english/resin
    2. https://www.merriam-webster.com/dictionary/resin
    3. https://wikidiff.com/resin/polymer
    4. https://www.sciencedirect.com/topics/engineering/liquid-resin
    5. https://www.aenor.com/normas-y-libros/buscador-de-normas/astm?c=044130
    6. https://www.matematicasypoesia.com.es/metodos/melweb08_Brookfield.htm
    7. https://www.matematicasypoesia.com.es/metodos/melweb08_Hoppler.htm
    8. https://www.smooth-on.com/support/faq/138/
    9. https://www.jiayuanfitting.com/info/iso-7619-1-rubber-harness-durometer-method-pdf-36090182.html
    10. https://webstore.ansi.org/standards/din/diniso76192012-1449738
    11. https://www.jiayuanfitting.com/info/iso-7619-2-rubber-harness-irhd-pocket-meter-pd-36090203.html
    12. https://www.collinsdictionary.com/dictionary/english/tensile-strength
    13. https://www.instron.us/testing-solutions/by-standard/astm/multiple-testing-solutions/astm-d412
    14. https://maclellanrubber.com/definitions/elongation-at-break
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