Cambridge Polymer Group uses several techniques to examine the chemical structure of polymers or other materials. When available, we test in compliance with published ASTM standards.

FTIR can identify the chemical structure of a molecule by measuring the absorbance of light at different frequencies. The absorbance is proportional to the concentration of the chemical species active at the selected frequency. When combined with a microscope (micro-FTIR), chemical concentration can be measured as a function of position. Curing of materials can be monitored with time-varying FTIR. Changes in chemical structure due to chemical reaction (e.g. the loss of double bonds in a monomer) can be quantified as a function of time. We perform oxidation index measurements per ASTM F2102-02. We also perform attenuated total reflectance (ATR) spectroscopy to measure the chemical signature of species on the surfaces of samples.

We perform testing in compliance with the following ASTM standards:

• F2101 Standard guide for evaluating the extent of oxidation of ultra-high molecular weight polyethylene fabricated forms intended for surgical implants
• F2381 Standard test method for evaluating trans-vinylene yield in irradiated ultra-high molecular weight polyethylene fabricated forms intended for surgical implants by infrared spectroscopy
• F1252 Standard practice for general techniques for obtaining infrared spectra for qualitative analysis

Vitamin E, or tocopherol, is an antioxidant used in countless applications, particularly in consumer products and in a growing number of biomedical materials. We can quantify the amount of Vitamin E in a sample using FTIR analysis. With micro-FTIR we can determine the Vitamin E concentration profile throughout the sample; we can also determine the average Vitamin E concentration using standard FTIR techniques.

DSC can be used to measure the degree of crystallinity, glass transition temperature, heat capacity, and melting point of a polymer sample. DSC can also provide information about oxidation resistance, degradation behavior, and solvent loss. Modulated DSC (mDSC) is a newer technique that can isolate kinetic events, such as degradation or annealing of imperfectly formed crystals, from non-kinetic events, such as melting or glass transitions.

We perform testing in compliance with the following ASTM standards:

• D3418 Test method for transition temperatures of polymers by differential scanning calorimetry
• D3895 Standard test method for oxidative-induction time of polyolefins by differential scanning calorimetry
• F2625 Measurement of enthalpy of fusion, percent crystallinity, and melting point of ultra-high molecular weight polyethylene by means of differential scanning calorimetry
• E2009 Standard test method for oxidation onset temperature of hydrocarbons by differential scanning calorimetry

GPC provides quantitative information about the molecular weight distribution (MWD) of a polymer sample. A polymer’s MWD can influence its mechanical, rheological, optical, and electrical properties. Knowledge of the MWD is also needed to determine processing conditions for polymer melts.

Swell ratio testing is usually conducted on crosslinked materials. In this test, a sample is placed in a good solvent at a particular temperature, and the change in height of the sample is monitored as a function of time. The crosslink density and molecular weight between crosslinks can be calculated from the final swell ratio using details of thermodynamic interaction between the sample and the solvent. Go to the application note section for an application note on this technique. This technique is in compliance with ASTM F2214-02. We also perform routine density testing with the density column technique.

We perform testing in compliance with the following ASTM standards:

• F2214 Standard test method for in situ determination of network parameters of crosslinked ultra high molecular weight polyethylene
• D2765 Standard test methods for determination of gel content and swell ratio of crosslinked ethylene plastics
• D1505 Standard test method for density of plastics by the density-gradient technique

EDS is used in conjunction with scanning electron microscopy to determine the elemental composition at the surface of a sample. Spot scans can analyze particulate matter on the surface, while two-dimensional area mapping can quantify the percentage elemental makeup of a chosen area. EDS can typically identify elements with atomic weights as low as that of Carbon.

The surface energy of a substrate can be measured with a variety of techniques. CPG performs contact angle measurements per ASTM D5946-01. In this technique, a 5-8 microliter drop of test liquid is placed on the surface of the test substrate. The resultant contact angle is measured from optical micrographs of the drop. Advancing and receding contact angles can be measured with our Dynamic Contact Angle Analyzer, using the Wilhelmy plate technique. The DCA can also be used to measure the surface tension of liquids using the DuNouy Ring technique.

We perform testing in compliance with the following ASTM standards:

• D5946 Standard test method for corona-treated polymer films using water contact angle measurements