STRUCTURAL EVALUATION STRUCTURAL EVALUATION OF MATERIALS BASED ON OF MATERIALS BASED ON

XANTHAN GUM AND LIGNINXANTHAN GUM AND LIGNINIrina Elena Raschip, Maria-Cristina Popescu

“Petru Poni” Institute of Macromolecular Chemistry, iecoj@icmpp.ro

COST Action FP1105: Understanding wood cell wall structure, biopolymer interaction and composition: implications for current products and new materials

San Sebastian, Spain, 25-28 May 2015

Why xanthan gum and Why xanthan gum and lignin?lignin?

• XanthanXanthan - thickening agent, emulsifier, stabilizer - thickening agent, emulsifier, stabilizer qualities, its ability to form films, together with the qualities, its ability to form films, together with the possibility of applications in various areas (food possibility of applications in various areas (food industry, cosmetics and pharmacy);industry, cosmetics and pharmacy);

• due to its characteristics (nano-size particles, due to its characteristics (nano-size particles, amorphous polymer, nontoxic and biodegradable amorphous polymer, nontoxic and biodegradable polymer, antibacterial and antioxidant properties), polymer, antibacterial and antioxidant properties), LigninLignin can be considered as a material providing many can be considered as a material providing many opportunities in various application fields, such as opportunities in various application fields, such as nanotechnology, medicine and pharmaceutical nanotechnology, medicine and pharmaceutical domains, agricultural, biomaterial, and packaging domains, agricultural, biomaterial, and packaging industries;industries;

• Xanthan incorporation leads to an increase of the Xanthan incorporation leads to an increase of the thermal stability, hydrophilicity, biocompatibility, thermal stability, hydrophilicity, biocompatibility, biodegradability of the films. biodegradability of the films.

•elaboration of hydrogels based on xanthan gum (X) and different types of lignin in order to develop matrix sustained-release of highly water-soluble

•the work was carried out in order to gain better understanding on morphology and specific interactions within xanthan–lignin systems.

The materials used and their The materials used and their characteristics characteristics

Xanthan gum – E 415 (FDA)molecular weight is been reported to be Mw ~ 3,5 x 106 g/molwhite or lightly yellow solid powder

Hydrogel-film preparationHydrogel-film preparation

• the xanthan gum and lignin were mixed with the xanthan gum and lignin were mixed with NaOH solution, and then EPC was added under NaOH solution, and then EPC was added under vigorously continuous stirring. The mixtures vigorously continuous stirring. The mixtures gels-like were lied on glass plates and the gels-like were lied on glass plates and the crosslinking reaction was performed for 8 h at crosslinking reaction was performed for 8 h at 80 80 00C. After crosslinking, the hydrogels were C. After crosslinking, the hydrogels were washed out until it was observed that washed out until it was observed that approximately 97% of EPC was removed from approximately 97% of EPC was removed from the system.the system.

Morphology studyMorphology study

70X/30HpHL 70X/30GL

• all hydrogels presents spherical domains which seemed to be encapsulated in the matrix

• the images of the hydrogels showed homogenous distributions and continuous film formations, indicating an excellent interaction between the two components

• the presence of pores on the scanned area it is observed; porous structure characteristics depend on the lignin type

FT-IR examination of the hydrogels

• in the FT-IR spectra of hydrogels all bands are broader proving that the crosslinking took place

• using the wavenumber corresponding to the OH stretching vibration, the energy of the H bonds can be calculated

• this has values between 16.9 and 17.3 kJ for intramolecular H bonds and 25.1 and 27.3 kJ for intermolecular H bonds, and order of its variation in respect with lignin types is:

X/AWL > X/HpHL > X/PL > X/CL > X/GL

The sorption isotherms are a typical combination of classic IUPAC type III and I isotherms for sorption and desorption.

The sorption capacity of the hydrogels varies with the type of lignin used.

Water uptake at maximum RH increases in all hydrogels in comparison to X, the highest one being the X/GL hydrogel (34.18 wt%).

Sorption isotherms plotted as a function of sample relative humidity of the X and X/L

hydrogels

ConclusionsConclusions• The obtained hydrogels own high water vapor sorption capacities,

good mechanical properties such as high strength and stiff structure.• SEM indicates that the lignin type influences the hydrogel morphology

leading to formation of different porous structures with a smooth surface, excepting the hydrogel containing AWL which form a fibrilar structure.

• FT-IR spectroscopy: interactions between the two components leading to the formation of new hydrogen bonds and of crosslinked structure. The energy of the hydrogen bonds is higher for the hydrogel containing AWL suggesting stronger intermolecular interactions.

• Lignin role as antimicrobial agent and thermal stabilizer in xanthan/lignin hydrogels depends on lignin type and characteristics.

• These materials have potential in different fields of applications.