Starch-grafted-poly(ɛ-caprolactone) copolymers: synthesis and use as blends compatibilizer

OLIVIA V. LÓPEZ; MARIO D. NINAGO; SOLEDAD M. M. LENCINA; NOEMÍ A. ANDREUCETTI; ANDRÉS E. CIOLINO; MARCELO A. VILLAR

Río de Janeiro

Conferencia; Fifth International Conference on Natural Polymers, Biopolymers and biomaterials: Applications from macro to nanoscale; 2017

Thermoplastic starch (TPS) can be obtained by processing native starch at high temperature and shear stress in the presence of enough plasticizers such as water, glycerol, and sodium alginate, among others. Starch based materials present some disadvantages mainly associated to their high susceptibility to humidity, limiting its industrial applications. In this sense, starch blending with others polymers, particularly poly(ɛ-caprolactone), PCL, may represents a promising alternative to improve final properties of starch-based materials. Nevertheless, due to hydrophilic starch and hydrophobic PCL characters, the compatibility between them is very low. Within this context, the use of a compatibilizer agent could overcome this drawback. In this work, a PCL grafted starch was obtained as candidate for enhancing TPS-PCL blends compatibility. Copolymer was synthesized by low doses of 60Co gamma radiation, being a novel, simple, and green one-pot technique. Before the irradiation process, samples preparation included the mixture of a gelatinized starch suspension (S) and ε-caprolactone monomer (CL), obtaining a starch:monomer mass ratio of 1:0.1 (S-g-CL). After irradiation, samples were freeze-dried and repeatedly extracted in chloroform to separate the unreacted ε-caprolactone monomer and non-grafted PCL. Fourier Transform Infrared (FTIR) analysis allowed corroborating the presence of PCL grafted on starch granules by detecting the characteristic band of stretching vibration of carbonyl groups at 1710 cm-1. The compatibilizing effect of S-g-CL over two TPS-PCL blends was tested. One of the thermoplastic starches employed was obtained from the native corn starch (S) melt-processing with 35 % w/w glycerol (G), named as SG. The other TPS was processed by adding 10 % w/w sodium alginate (A) as additional plasticizer, named as SGA. Thermoplastic starches, SG and SGA, were blended with PCL (10:90 mass ratio) and S-g-PCL (0, 2.5 and 5 % w/w) was included as compatibilizer agent. Blends were melt-mixed and further injected and thermo-compressed. Resulting films were translucent, flexible, and easy to handle, regardless the compatibilizer incorporation. By Scanning Electron Microscopy (SEM) and FTIR, it was evidenced the PCL presence within the SG and SGA matrices. Mechanical behavior of the studied SG/SGA-PCL blends was evaluated through tensile tests. Results demonstrated that the presence of S-g-CL improved the compatibility between the two polymers, enhancing the performance of the final materials.