ASTM  D5225 Measuring Solution Viscosity of Polymers with a Differential Viscometer

Introduction 

The ASTM D5225 test focuses on the solution viscosity measurement of a polymer using either an ordinary or differential viscometer. This test can be applied to any polymer that dissolves in a solvent without the involvement of any chemical changes or decomposition, resulting in a stable solution. The viscosity data accompanying this determination is more often than not referred to as specific, intrinsic, inherent, or relative viscosity, which gives information about the molecular weight and structure of the given material. The viscosity determined has been compared with earlier methods where glass capillary tubes are used (Test Method D2857, for instance). Still, one can use the polymer solution and outdoor solvent for a more reliable determination of polymer viscosity.

Scope

The ASTM D5225 test method specifies using a differential or modified differential viscometer to determine the solution viscosity of polymers. This test applies to all polymers that dissolve entirely without a chemical reaction or degradation, forming stable solutions over time and temperature. The differential viscometer utilized in the test can measure all types of synthetic polymers, biopolymers, proteins, and peptides. The ASTM D5225 test method also allows for quick viscosity characterization of polymers.

Procedure

The ASTM D5225 test employs a balanced network of four capillaries organized in a  Wheatstone bridge-like pattern. Pure solvent flows via a balanced capillary network at constant inlet pressure Pi, resulting in a zero or baseline pressure on the differential pressure transducer.  Sample reservoir A is filled with the solution and injected upstream via the switching valve SA. The differential pressure rises until it reaches a steady-state value of ∆P, proportional to the solution’s viscosity. The differential pressure is continuously monitored on a strip chart recorder or computer, providing a baseline against which ∆P is recorded.

Specimen Size

The test materials in ASTM D5225 are mandatorily polymer solutions. The polymer must be fully soluble in the solvent chosen for the study without reacting or decomposing. The size of the specimen is influenced by the types of polymers and their concentration. Still, it is typically made to ensure that the specimen is entirely dissolved to give a stable solution that can be used for effective viscosity determination.

Result 

The ASTM D5225 test results are usually expressed as specific, intrinsic, inherent, or relative viscosity. According to ASTM D5225, the viscosity of a polymer solution is proportional to the average molecular size of the polymer component that dissolves in the solvent.

Conclusion

The ASTM D5225 test method offers a uniform procedure to evaluate the viscosity of polymer solutions using either a differential or modified differential viscometer. This test applies to all polymers, which can be entirely dissolved without reaction or thermal degradation, leading to stable solutions. The Polymer Solutions Measurement in Diluents viscometry ASTM D5225 is a more accurate method than the others since both polymer solution and solvent are measured at the same time. Shear stress measurements such as, but not limited to, specific, intrinsic, inherent, or relative viscosity measurements are influenced by the size/volume of the polymer’s molecules. This includes synthetic and natural polymers, making a viscosity measurement possible quickly and conveniently.

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