Determination of Crosslink Density, Extent of Crosslinking, Swell Ratio or Gel Fraction
Crosslink density is measured using ASTM D 2765 – 01 as a guidline. This can include determination of the gel content and the swell ratio as desired. Additional information about network parameters can be obtained for specific polymer types using methods such as ASTM F 2214 – 02 “Standard Test Method for In situ Determination of Network Parameters of Crosslinked Ultra High Molecular Weight Polyethylene (UHMWPE).” Specialized methodologies have been developed for testing of other crosslinked polymer systems and are available upon request.
Extractables and Leachables Testing
Polymer samples are cryoground if desired and subjected to soxhlet extraction for a specified period of time. Polar and nonpolar solvents can be applied depending on if it is desired to determine the extractable or leachable components in the sample. Alternatively, the sample is placed into a suitable solvent in a metal wire cage and extracted for a specified period of time. Gravimetric analysis of the residual sample is used to determine the percent extractables. This technique can be coupled with mass spectroscopy to determine the chemical structures of the extracted species. Spiking studies can be performed to confirm extraction efficiency.
The sample is prepared for analysis by extraction, precipitation, or ashing depending on the quantitation desired. The residual weight is then measured on an analytical balance. Duplicate samples are analyzed to demonstrate the reproducibility of the method.
High Temperature Filtration (Filter-H)
This process includes sample filtration using trichlorobenzene (TCB) at high temperature (approximately 145 C).
Karl Fischer Titration
The sample is dissolved in a suitable solvent. The volume of water is then determined by titration using Karl Fischer reagent.
Solid Phase Extraction (SPE)
SPE is a technique used to purify or concentrate an analyte from a sample matrix by selectively retaining and eluting the compounds of interest. This is an excellent method for removal of interferences (unwanted species). Mechanisms for SPE include anion and cation exchange, reversed and normal phase.
Jordi Labs will attempt to determine a suitable solvent to dissolve your sample. The chemistry of the sample influences solvent choices. Jordi Labs has a large number of specialty solvents for polymer analysis including perfluoro solvents and a wide range of organic and buffer solutions.
Specific Gravity or Relative Density
Specific gravity is a technique used to define the ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4C (39F) and 1 atm. Substances with a specific gravity greater than one are denser than water, and so (ignoring surface tension effects) will sink in it, and those with a specific gravity of less than one are less dense than water, and so will float in it.
A wide range of titrations are available including acid/base, hydroxyl number, and various ASTM methods upon request. The sample is placed into a suitable solvent and titrated using the appropriate titrant. The volume of titrant is used to determine the concentration of the titrated species in the solution. Samples are generally run in duplicate to demonstrate reproducibility of the method.
This method allows removal of low molecular weight impurties (<10K) from aqueous solutions. A range of molecular weight cut-offs can be chosen. This method can be used to remove salts, residual monomers or other impurities from polymer solutions. Some alcohol solutions can also be analyzed by this method.