Identification and measurement of intermolecular interaction in polyester/polystyrene blends by FTIR-photoacoustic spectrometry

Authors: Gordon, Sherald; MOHAMED, A - King Saud University; Harry O Kuru, Rogers; Biresaw, Girma

Submitted to: Journal of Polymers and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2015
Publication Date: 11/3/2015
Publication URL: https://handle.nal.usda.gov/10113/62315
Citation: Gordon, S.H., Mohamed, A.A., Harry-O'Kuru, R.E., Biresaw, G. 2015. Identification and measurement of intermolecular interaction in polyester/polystyrene blends by FTIR-photoacoustic spectrometry. Journal of Polymers and the Environment. 23(4):459-469.

Interpretive Summary: Infrared spectrometry is a technique that uses infrared light to measure the concentrations of various components including polymers in materials such as plastics. In use, the sample is exposed to infrared light of various wavelengths and a detector determines how much of each wavelength is absorbed by the components. An infrared spectrum results after testing. This technique can be used to determine structures present in a polymer as well as whether a given polymer is interacting with other polymers or other smaller chemicals in the system. A new infrared spectrometry method was devised to reveal and identify a rare type of intermolecular interaction formed in plastic made from blends of polystyrene with each of three biodegradable polyesters. This new infrared method permits the quantitative measurement of the degree of interaction between the two polymers in the plastic. The method uses a computer technique called spectral curve fitting which is a mathematical way of taking a spectrum apart and exposing its hidden component spectra that contribute to the total spectrum obtained. Curve fitting spectra of the plastics into their underlying component spectra revealed the presence of the intermolecular interaction formed when a polyester binds to polystyrene. The results indicated that the amount of interaction formed depends on the type and concentration of the biodegradable polymer in the blend. Unlike current spectral curve-fitting methods, this new technique monitors changes in component distributions and estimates infrared absorptivity constants of all the hidden component spectra. This new method is applicable to polymer blends in general and will enable researchers to obtain fundamental knowledge needed to tailor biodegradable plastics to develop new formulations that will have higher value in targeted end-uses.

Technical Abstract: Fourier transform infrared photoacoustic spectrometry was used to reveal and identify n-p type intermolecular interaction formed in plastic comprising binary blends of polystyrene and a biodegradable polymer, either polylactic acid, polycaprolactone or poly(tetramethyleneadipate-co-terephthalate). Also, an infrared method was devised that permits quantitative measurement of the degree of interaction between the two polymers at various concentrations in the blends. The method employs spectral deconvolution by least squares curve fitting of the polymer carbonyl band into its underlying peaks. In a new algorithm the method compares deconvoluted Gaussian/Lorentzian peaks of the polymer blends with deconvoluted peaks in the neat polymers and computes both the magnitude and direction of change in the n-p bond formation with change in polymer concentration. The results indicated that the degree of interaction was dependent on the type and concentration of the biodegradable polymer in the blend. These findings are supported by differential scanning calorimetry and thermogravimetric analyses. Unlike conventional spectral deconvolution methods, this technique with its new algorithm approximates infrared absorptivities of all the underlying peaks, and is thus a superior method that should be applicable to multicomponent polymer blends in general.