1. Chemical, morphological and biodegradation studies in nanofibrillated cellulose (NFC) films for use in biocomposites
J. Santana,1 V. de Zea Bermudez2,4, G. Marques1,3, P.L. Silva1,2, A.Rebelo1
1 Engineering Department, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal
2 CQ-VR, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal
3 Agronomical Department and CITAB-Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal
4 Chemistry Department, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal
ABSTRACT
INTRODUCTION
RESULTS
DISCUSSION
Films of nanofibrillated cellulose (NFC) were characterized to serve as a reinforcement agent in biocomposites matrix intending to improve their mechanical properties, such us structural strength, heat resistance and interface adherence [1] [2]. Although NFC’s would be already a good contender for this purpose, since they are constituted of nano whisker, needlelike, crystals [3] [4] it´s still necessary to verify if the process of film making would not change the chemical and morphological structure in a way that would diminish the same properties they are supposed to increase. For the least, it is necessary to verify the degradation properties of NFC, since the goal it´s to find a “complete” “green” material.
With this principle in mind, NFC films were obtained by two different drying methods, with first being achieved with an electric stove and the second trough a desiccant reaction (P2O5). To investigate changes in the morphological and chemical structure, the material was analyzed via SEM, EDS, DRX and FTIR. For biodegradation studies, a strain of Pleurotus ostreatus was inoculated in the NFC film and in the standard culture media for fungi, Potato Dextrose Agar (PDA), aiming to compare the growth rate in the two media.
SEM pictures showed agglomeration of fibers forming a compacted pad with a flat surface that EDS and mapping analyses revealed to be constituted of C, Na, Si, Ca as major constituents. Crystalline Index was attested in 55% [9] and FTIR verified that NFC films possess C-O, H-O connections [5] [6].The growth rate of the inoculated fungi in the NFC film revealed that the fungi developed in the sample almost as fast as in PDA, pointing that an NFC constituted material can be easily biodegradable by aerobic biological processes.
In recent years the usage of plant based materials for technological advancement have attracted significant interests of researchers due the decay of petroleum reserves and the need to protect the environment. Some of that attention was given to the usage of that type of materials as a reinforcement in polymer composites [1], [2]. Cellulose is synthesized by many organism like marine animals, fungi, bacteria and plants [3]. In plans and trees cellulose is abundant, being a constituting of cells walls as structural polymer. It is obtained through the process of photosynthesis that needs mainly water, carbon dioxide and solar energy to occur [2]. In Plant cell walls, cells are complex layered structures constituted by one primary wall encircling a secondary wall. The secondary wall is also a complex layered structure consisting of cellulose, hemicellulose and lignin. Nanocelulose can be obtained from plant cell walls by the removal of the amorphous regions (hemicellulose and lignin). Depending on the method of extraction different types of nanocellulose can be extracted, mainly nanofibrils cellulose (NFC) and nanocrystals cellulose (CNC). NFC's can produced by various methods and posseses attractive properties like, large surface area, high elastic modulus, high aspect ratio, low thermal degradation, non-toxicity [4] and biodegradability [5].
Scanning electron microscopy (SEM) shows fiber packing, although presence of single fibers can still be notice, such occurs due the loss of water content during film making. elements like C, Cl, C, Ca, Na, Mg, Si, S, Cl and K are founded in different quantities. The presence of that elements suggest that the chemical treatment in witch water was used, was done with drinkable water. Ftir spectra attained showed peaks at 3400 cm-1, corresponding to an O-H vibrations due to vibrations of hydrogen bonded hydroxyl group. At at 2900cm-1 corresponding to C-H stretching vibrations present in cellulose molecules (C-H form CH2). Finally at 1640 cm-1 there is a peak associated with O-H vibration bending of absorbed water. Crystallinity according to Segal method was determined as follows:
𝐼 𝐶 = 𝐼 002 − 𝐼 𝑎 𝐼
Evaluation shows that NFC possess a degree of crystallinity of 55%. Degradation test assure that NFC films are “green” , with a rate of degradation close to the one found in PDA.
Figure 1. SEM images of NFC films
Figure 2. SEM images of NFC film inoculated with P. ostreatus
CONCLUSIONS
METHODS AND MATERIALS
The results of the procedures applied in this work have shown that NFC seems to maintain its characteristics after filmmaking, with booth drying methods. Results also support the idea that the NFC may be used in biocomposites. The growth rate of the inoculated fungi in the NFC film revealed that the fungi developed in the sample almost as fast as in PDA, pointing that an NFC constituted material can be easily biodegradable by aerobic biological processes.
Commercial nanocellulose (pulp, 97% wt.; University of Maine) was used to produce films placing cellulose nanofibers in a oven at 60oC for 8 hours and by dehydration using P2O5 .
Characterizing techniques:
SEM (Figure 1,2), EDX and mapping (Figure 3).
X-ray diffraction.
FTIR (Table1).
Biodegradable properties of both samples were assessed in terms of P. ostreatus and PDA (potato dextrose agar) growth rate, at constant conditions of pressure and humidity
Figure 3. Mapping
Figure 4. Films after degradation
3400cm-1
2900cm-1
1640 cm-1
O-H
C-H
CONTACT
Table 1. FTIR results
REFERENCES
[1] Herrera-Franco, L.T. Drzal, “Comparison of methods for the measurement of fibre/matrix adhesion in composites,” Composites, p. 2–27, January 1992.
[2] Perrine Bordes, Eric Pollet, Luc Avérous, “Nano-biocomposites: Biodegradable polyester/nanoclay systems,” Progress in Polymer Science, p. 125–155, February 2009.
[3] Mariana Pereda et al.“Structure and properties of nanocomposite films based on sodium caseinate and nanocellulose fibers,” Journal of Food Engineering, p. 76–83, 30 October 2010.
[4] Hon-Meng Ng, et. al., “Extraction of cellulose nanocrystals from plant sources for application as reinforcing agent in polymers,” Composites Part B, pp , 14 January 2015.
[5]. L. Segal. et. al., “An Empirical Method for Estimating the Degree of Crystallinity of Native Cellulose Using the X-Ray Diffractometer,” Textile Research Journal, pp , October 1959.
[6]. Song z . et. al., “Hydrophobic-modified nano-cellulose fiber/PLA biodegradable composites for lowering water vapor transmission rate (WVTR) of paper,” Carbohydrate Polymers, p. 442–448, 21 April 2014
João Santana
UTAD