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Euro Polymer Science 2020 Characterization of components isolated from algerian apricot shells (prunus armeniaca l.) - Djennat Allouch, University Chadli Bendjedid El Tarf.

Djennat Allouch

Shells resulting from food processing and agricultural activities, such as hard shells of apricot, are considered as wastes and are  generally used as fuel. However, this residue shows  promise as lignocellulosic feedstock for biorefineries, for its  conversion  to liquid  fuel  or  bio-products.  This  study  is  dedicated  to  the  characterization  and  isolation  of lignin, cellulose  and  hemicelluloses from  apricot  shells  (AS).  The chemical  composition  and  thermal  stability  of  AS  after chemical  treatment with  solvents  (ethanol-toluene),  cellulose,  hemicelluloses and  lignin  were  analyzed by  standard methods, i.e.  Fourier-transform infrared spectroscopy (FTIR) and  thermogravimetric analysis (TGA). Further,  almost 50.2 wt% of a water-insoluble  extract was obtained after  the  bleaching process, which  showed  the removal of lignin, and  the  final  percentages  for  this  extraction  were  50.2  ± 0.34%,  26.5  ±  0.83%,  23.7  ±  0.29%  and  35  ±  1%  for holocellulose, cellulose,  hemicelluloses and lignin,  respectively. FTIR spectroscopy evidenced the structure  of lignin, cellulose  and  hemicelluloses.  Thermal  analysis  and  the  kinetic  study  suggested  that  cellulose  had  higher  thermal stability than the other  components, with the activation  energy of 289.62 kJ/mol.  Thus,  our results indicated the  high potential of AS to be used as an environmentally friendly material in a biorefinery, as  well  as  in the  modern  polymer and chemical industries. 

INTRODUCTION: The rapid increase in agricultural wastes is one of  the  major  environmental  concerns,  since  the disposal of these wastes on the soil or in landfills causes  serious  environmental  problems.  This problem  has  turned  the  researchers’  attention towards  the  valorization  of  agricultural  residues, as well as towards the development of recyclable or biodegradable products.1,2 Thus, the generation of  lignocellulosic  residues  as  agro-industrial by-products poses a challenge from the point of view of  environmental  protection,  as  well  as  for  the progress of a “green” economy.3-5  Lignocellulosics are the most abundant  source of insufficiently exploited  biomass  on  the  earth.  

They mainly consist  of  three polymers: cellulose, hemicelluloses  and  lignin,  representing the  three main  constituents of  the  cell  walls  of  plants, in which  they  are  not  uniformly  dispersed.  The structure  and  quantity  of  these  plant  cell  wall components vary according to the species, tissues and harvesting period.2 In general, lignocellulosic biomass  is  composed  of  40-50%  cellulose,  25-30% hemicelluloses and 15-20% lignin, as well as a small amount of other extractives.6 Prunus  armeniaca  L.  is  classified  under  the Prunus  species  of the  Prunaidea  sub-family  and the  Rosaceae  family.  At  present,  the  apricot  is cultivated in a diverse area with suitable climates.

EXPERIMENTAL

Materials and methods  Raw materials, chemicals and pretreatment methods Apricot  fruits  (P.  armeniaca  L.)  were  collected from the  Menna  region, located  in Batna in  the North East of Algeria. The apricot shells obtained were dried at room temperature during several days, ground by an electric mixer to a fine powder and sieved over a 20-80 mesh  screen  to  maintain  the  size  uniformity  of powdered  shells, as  per previous  National Renewable Energy Laboratory NREL standard methods. The dry powder of AS (20 g) was extracted with a 2:1  v/v ethanol/toluene  (300  mL)  mixture  for 8  h  to remove phenolics, pigments, wax and oils, followed by oven-drying at 50 °C for 24 h. The treated powder was used to find out the content of holocellulose, cellulose, hemicelluloses  and lignin,  and was  stored at  4  °C for further analysis.  The  chemicals  used  in  the  present  study  were  the following:  potassium  hydroxide  (>97%)  purchased from  Merck  KGaA  Company,  Germany;  sodium hydroxide (>99%) from Merck KGaA Company; nitric acid  (>65%)  from  Chemical  Company,  Iasi;  acetone (>99.8%)  from  Chemical  Company;  sulfuric  acid (>96%)  from  Sigma–Aldrich; sodium  chlorite (>25%, Synth)  from  Merck  KGaA  Company;  glacial  acetic acid (>99.8%)  from Chemical  Company, Iasi;  ethanol (99.5%, Synth) from Chemical Company, Iasi; toluene (>99%) from  Chemical  Company,  Iasi;  hexane (>99.8%) from Chemical Company, Iasi. 

Physico-chemical composition

The  chemical  composition,  moisture  (%)  and  ash (%)  content  of  the  apricot  shells  were  determined according to the standard methods of NREL,with the exception  of  holocellulose, which  was determined  by the  sodium  chlorite  method.The  average  of  three replicates was calculated for each sample. 

Isolation of acid insoluble lignin 

An  amount  of  AS  extracted  powder  of  1  g  was mechanically  stirred  in  15  mL  of  72%  H2SO4  (v/v) aqueous solution at 25 °C, in the powder/solution ratio of  1:15  (g/mL),  for  2.5  h.  The  suspension  was subsequently  diluted  with  200  mL  of  distilled  water and heated at 90 °C for 1 h. Then, it was filtered on a sintered  glass  crucible  G3  filter  and washed  with  hot distilled  water until  neutral  pH  was reached.  Finally, drying  was  carried  out  in  an  oven  at  105  °C  until constant mass was reached. 

 Isolation of cellulose and hemicelluloses

Separation of holocellulose  An amount  of  5 g  of  extracted powder was  mixed with 150 mL of distilled water, in the presence of 1.5 g of sodium chlorite and 10  drops  of glacial acetic acid, for  one  hour  at  the  temperature  of  80  °C,  under mechanical stirring. After 1 h, 1.5 g of NaClO₂ and 10 drops of glacial acetic acid were  added to the mixture. The reaction  was continued  for 1  h and  was repeated for  4  times.  After  the  treatment,  the  holocellulose suspension  was  cooled  in  an  ice  bath,  filtered  on  a sintered glass crucible  G₂ filter,  washed with distilled water to neutral pH and then with acetone, and finally, was oven dried at 50 °C to constant mass. 

Separation of hemicelluloses 

An amount of 1 g of holocellulose was treated with 25  mL of  potassium  hydroxide  (15%) for  2 hours  at room  temperature  (25  °C).  It  was  then  filtered  on  a sintered glass crucible G2 filter, and the solid bleached phase obtained was cellulose, while the liquid fraction represented  the  hemicelluloses  content.  The  liquid fraction  was acidified  with  acetic acid  to pH  5-6  and then precipitated in 5 volumes  of  ethanol. The residue obtained was filtered  through a sintered  glass crucible G2 filter, washed with ethanol and finally oven dried at 50 °C to constant weight.  

 CONCLUSION

This work reports on the extraction of the main components  of  apricot  shell  biomass.  FTIR spectroscopy  and  TGA  have  been  used  to characterize them. The removal of lignin has been confirmed  by  the absence  of  the  peaks  at  1502, 1508  and  1612  cm-1  in  the  FTIR  spectra, suggesting  the  great  efficiency  of  the  bleaching process. TGA revealed that the cellulose extracted from the apricot shells has good thermal stability, followed  by  lignin,  treated  AS  and hemicelluloses. The analysis  of the FTIR spectra evidenced  the  structure  of  cellulose, hemicelluloses  and  lignin,  which  confirmed  that apricot  shells (AS)  are a  lignocellulosic  biomass source  with  relatively  high  cellulose, hemicelluloses  and  lignin  contents.  This  makes apricot  shells  (AS)  an  interesting  and advantageous  material  for  various  valorization methods.

This work is partly presented at 6^th Edition of International Conference on Polymer Science and Technology April 01-02,2020 Webinar