Title: Understanding Freezer Aging of Prepregs Using NIR Spectroscopy

Authors: Lara Fadel, Steven Nutt

DOI:

Abstract: Prepregs often reach expiration due to accumulated out-time or extended freezer storage beyond specified limits, resulting in the disposal of unused material. The study aims to identify the mechanism by which freezer storage affects prepregs, with a particular focus on the role of water. Additionally, a reliable and non-destructive diagnostic method was developed to quantify the remaining shelf life and reduce variability during composite manufacturing. The state of water within prepregs was monitored as a function of freezer aging using NIR (near-infrared) spectroscopy, KF titration, and differential scanning calorimetry (DSC). DSC data were also used to develop a cure kinetics model, while NIR spectra, along with other physics-based features, were used to develop a shelf-life prediction model. DSC measurements demonstrate that freezer aging alters the distribution of free and bound water, inducing ~12% advancement in degree of cure over our 41-week freezer aging study, compromising prepreg processability. Additionally, cure kinetic models indicated a corresponding reduction in cure rate as freezer aging duration increased. This work also demonstrates how NIR spectroscopy can be employed to monitor (and predict) freezer aging, showing high predictive capability for freezer-storage duration, achieving over 98% accuracy. This study experimentally validated previously misunderstood aging mechanisms during freezer storage and showed how NIR-based diagnostics provided a rapid and non-destructive method that can be deployed as a quality control tool to assess prepreg shelf life.

References: [1] [2] [3] [4] [5] G. Capiel, L. A. Miccio, P. E. Montemartini, and G. A. Schwartz, “Water diffusion and hydrolysis effect on the structure and dynamics of epoxy-anhydride networks,” Polym. Degrad. Stab., vol. 143, pp. 57–63, Sep. 2017, doi: 10.1016/j.polymdegradstab.2017.06.010. F. Zhang, R. Yang, and D. Lu, “Investigation of Polymer Aging Mechanisms Using Molecular Simulations: A Review,” Polymers, vol. 15, no. 8, p. 1928, Apr. 2023, doi: 10.3390/polym15081928. J. Orellana-Barrasa, A. Ferrández-Montero, B. Ferrari, and J. Y. Pastor, “Natural Ageing of PLA Filaments, Can It Be Frozen?,” Polymers, vol. 14, no. 16, p. 3361, Aug. 2022, doi: 10.3390/polym14163361. K. Nakamura, T. Hatakeyama, and H. Hatakeyama, “Relationship between hydrogen bonding and bound water in polyhydroxystyrene derivatives,” Polymer, vol. 24, no. 7, pp. 871–876, Jul. 1983, doi: 10.1016/0032-3861(83)90206-9. P. Musto, G. Ragosta, and L. Mascia, “Vibrational Spectroscopy Evidence for the Dual Nature of Water Sorbed into Epoxy Resins,” Chem. Mater., vol. 12, no. 5, pp. 1331–1341, May 2000, doi: 10.1021/cm9906809. [6] G. Odian, Principles of Polymerization, 1st ed. Wiley, 2004. doi: 10.1002/047147875X. [7] J. Kratz, K. Hsiao, G. Fernlund, and P. Hubert, “Thermal models for MTM45-1 and Cycom 5320 out-of-autoclave prepreg resins,” J. Compos. Mater., vol. 47, no. 3, pp. 341–352, Feb. 2013, doi: 10.1177/0021998312440131. [8] D. Kim, T. Centea, and S. R. Nutt, “Out-time effects on cure kinetics and viscosity for an out-of-autoclave (OOA) prepreg: Modelling and monitoring,” Compos. Sci. Technol., vol. 100, pp. 63–69, Aug. 2014, doi: 10.1016/j.compscitech.2014.05.027. [9] B. Dickens and S. H. Dickens, “Estimation of Concentration and Bonding Environment of Water Dissolved in Common Solvents Using Near Infrared Absorptivity,” J. Res. Natl. Inst. Stand. Technol., vol. 104, no. 2, pp. 173–183, 1999, doi: 10.6028/jres.104.012. [10] A. E. Krauklis, A. I. Gagani, and A. T. Echtermeyer, “Near-Infrared Spectroscopic Method for Monitoring Water Content in Epoxy Resins and Fiber-Reinforced Composites,” Materials, vol. 11, no. 4, Art. no. 4, Apr. 2018, doi: 10.3390/ma11040586. [11] R. D. Guha, E. O. Danilov, K. Berkowitz, O. Oluwajire, and L. R. Grace, “Consequences of Humidity Cycling on the Moisture Absorption Characteristics of Epoxy Resins with Different Network Architectures,” ACS Appl. Polym. Mater., vol. 5, no. 1, pp. 400–411, Jan. 2023, doi: 10.1021/acsapm.2c01570. [12] T. Theophanides, Ed., Infrared Spectroscopy : Materials Science, Engineering and Technology. IntechOpen, 2012. doi: 10.5772/2055. [13] G. R. Choppin and K. Buijs, “Near-Infrared Studies of the Structure of Water. I. Pure Water,” J Chem Phys, 1963. [14] O. Idolor, R. D. Guha, K. Berkowitz, C. Geiger, M. Davenport, and L. Grace, “Polymerwater interactions and damage detection in polymer matrix composites,” Compos. Part B Eng., vol. 211, p. 108637, Apr. 2021, doi: 10.1016/j.compositesb.2021.108637. [15] M. Frigione and J. M. Kenny, “Effects of storage aging on the cure kinetics of bismaleimide prepregs,” Adv. Polym. Technol., vol. 24, no. 4, pp. 253–265, 2005, doi: 10.1002/adv.20048. [16] N. Sharp, “Effects of moisture on the properties of epoxies and carbon-epoxy composite laminates,” Ph.D., Purdue University, United States -- Indiana, 2015. Accessed: Jul. 04, 2025. [Online]. Available: https://www.proquest.com/docview/1746685961/abstract/CF9D1B1EA31D4BD8PQ/1 [17] S. Popineau, C. Rondeau-Mouro, C. Sulpice-Gaillet, and M. E. R. Shanahan, “Free/bound water absorption in an epoxy adhesive,” Polymer, vol. 46, no. 24, pp. 10733–10740, Nov. 2005, doi: 10.1016/j.polymer.2005.09.008. [18] S. Miller, “Re-Certification and Equivalency Test Results for IM7/8552-1 Following Extended Freezer Storage,” May 21, 2018. Accessed: Jan. 08, 2026. [Online]. Available: https://ntrs.nasa.gov/citations/20180004930 [19] J. E. Bone et al., “On the relationship between moisture uptake and mechanical property changes in a carbon fibre/epoxy composite,” J. Compos. Mater., vol. 56, no. 14, pp. 21892199, Jun. 2022, doi: 10.1177/00219983221091465. [20] H. Obeid et al., “Evolution of physico-chemical and mechanical properties of bonded epoxy assemblies during hygrothermal cyclic aging,” Mech. Ind., vol. 24, p. 40, 2023, doi: 10.1051/meca/2023036. [21] C. Amare, O. Mantaux, A. Gillet, M. Pedros, and E. Lacoste, “Innovative test methodology for shelf life extension of carbon fibre prepregs,” IOP Conf. Ser. Mater. Sci. Eng., vol. 1226, no. 1, p. 012101, Feb. 2022, doi: 10.1088/1757-899X/1226/1/012101. [22] C. Amare, O. Mantaux, A. Gillet, and M. Pedros, “Simplification of requalification procedure of outdated carbon/epoxy prepregs and scenarios of reuse,” J. Phys. Conf. Ser., vol. 2526, no. 1, p. 012049, Jun. 2023, doi: 10.1088/1742-6596/2526/1/012049. [23] D. Kim and S. R. Nutt, “Effective cure cycle development via flow optimization and advanced cure environments,” Adv. Manuf. Polym. Compos. Sci., vol. 6, no. 3, pp. 164–172, Sep. 2020, doi: 10.1080/20550340.2020.1815276. [24] R. W. Jones, Y. Ng, and J. F. McClelland, “Monitoring ambient-temperature aging of a carbon-fiber/epoxy composite prepreg with photoacoustic spectroscopy,” Compos. Part Appl. Sci. Manuf., vol. 39, no. 6, pp. 965–971, Jun. 2008, doi: 10.1016/j.compositesa.2008.03.015. [25] M. Salzmann, M. Teuchtmann, and R. Schledjewski, “Determination of the glass transition temperature of an epoxy prepreg by Near Infrared Spectroscopy,” Polym. Test., vol. 125, p. 108111, Aug. 2023, doi: 10.1016/j.polymertesting.2023.108111. [26] W. Li, Y. D. Huang, and P. Chen, “Use of Near-Infrared Spectroscopy for On-Line Monitoring the Quality of Prepreg Cloth,” Adv. Compos. Lett., vol. 17, no. 2, p. 096369350801700201, Mar. 2008, doi: 10.1177/096369350801700201. [27] “CYCOM 5250-4,” Syensqo. Accessed: Jan. 08, 2026. [Online]. Available: https://www.syensqo.com/en/product/cycom-5250-4 [28] “HexTow Laminate Properties in HexPly® 8552 | Hexcel.” Accessed: Jan. 08, 2026. [Online]. Available: https://www.hexcel.com/Products/Resources/1664/hextow-laminateproperties-in-hexply-8552 [29] “3900 Prepreg System,” Toray Composite Materials America, Inc. Accessed: Jan. 08, 2026. [Online]. Available: https://www.toraycma.com/3900-prepreg-system/

Conference: SAMPE 2026

Publication Date: 2026/04/27

SKU: 21

Pages: 13

Price: $26.00