Surface cross-linked thermoplastic starch with different UV wavelengths: mechanical, wettability, hygroscopic and degradation properties

Peng Yin; Chunhao Chen; Hongpeng Ma; Huijuan Gan; Bin Guo; Panxin Li

doi:10.1039/d0ra07549c

Surface cross-linked thermoplastic starch with different UV wavelengths: mechanical, wettability, hygroscopic and degradation properties

RSC Adv. 2020 Dec 18;10(73):44815-44823. doi: 10.1039/d0ra07549c. eCollection 2020 Dec 17.

Authors

Peng Yin¹, Chunhao Chen¹, Hongpeng Ma¹, Huijuan Gan¹, Bin Guo^{1

2

3}, Panxin Li^{2

3}

Affiliations

¹ College of Science, Nanjing Forestry University Nanjing 210037 China gbm@ustc.edu +86 25 85427625.
² Agricultural and Forest Products Processing Academician Workstation Luohe 462600 China.
³ Post-Doctoral Research Center of Nanjiecun Group Luohe 462600 China.

Abstract

Here, we report a method to improve the properties of thermoplastic starch (TPS) by surface ultraviolet (UV) cross-linking. TPS sheets were prepared by injection molding and coated with an ethanol solution of photo-initiator TPO (2,4,6-trimethyl benzoyl diphenyl phosphine oxide), then, irradiated by UV with different wavelengths for 15 min. Untreated and irradiated TPS sheets were characterized using tensile and bending tests, impact tests, dynamic mechanical thermal analysis (DMTA) and infrared spectroscopy (FTIR). FTIR spectra showed that UV irradiation can effectively trigger surface cross-linking of TPS sheets. The mechanical and dynamic mechanical properties of the TPS were improved and the optimized properties were obtained by 308 nm UV irradiation. A tensile strength of 4.1 MPa, a bending strength of 2.7 MPa, an impact strength of 96.8 kJ m^-2, and the corresponding activation energy of 251.22 kJ mol^-1 were obtained. The water contact angle and moisture absorption of the samples were also investigated and the 308 nm UV irradiated sheets have a contact angle of 74°. Moisture absorption rate as a function of the square root of time showed a sigmoid curve including a linear stage which conforms to Fick's second law. The samples irradiated by 308 nm UV had the lowest equilibrium moisture absorption rate M _∞ and the longest time T ₀ to enter into the Fick's diffusion stage and the lowest slope K and diffusion coefficient D. All samples displayed biodegradable properties when buried in soil. This method has potential applications for agricultural mulch films, packing and medical film products.