Annals of Warsaw University of Life Sciences - SGGW

Another explanation can be fast consumption of antioxidant at the beginning of aging process.
But rather the most probably reason of this phenomenon is the occurrence of amorphous
regions, which are more susceptible to degradation. So, at the beginning of aging process,
cellulose degradation mainly proceeds in the most accessible regions and decrease of the
weight average polymerization degree of cellulose is the highest – for cellulose with PG and
THBP. These assumptions are in agreement with the results of cellulose crystallinity index
[Antczak 2010]. Results obtained for cellulose with EQ (Fig. 2) indicate that etoxyquin better
inhibit cellulose degradation than other antioxidants, especially at the beginning of aging
process. After 6 days cellulose degradation poceeds probably mainly in amorphous regions.
Prove it the results of cellulose crystallinity index [Antczak 2010].
In relation to thermal aging of extracted and non extracted wood the results presented
in Fig. 3 indicate that cellulose in non extracted wood is the most degraded. Similarly as for
cellulose with synthetic antioxidants, the presence of low molecular substances (extractives)
accelerates thermal degradation of cellulose. Increase of cellulose degradation susceptibility
in 130ºC in air atmosphere, probably can be caused by formation additional products from
thermal decomposition or oxidation of synthetic antioxidants and extractives. These
substances may have radical or hydroperoxide character. Such, very reactive products may
contribute to effective degradation of cellulose chains [Kolar 1997].
(DPw)×10 -3
2,7
2,2
1,7
1,2
Thermal aging in nitrogen atmosphere
18
R 2 = 0.9919
0 3 6 9 12 15 18
aging time/days
cellulose
cellulose with EQ
cellulose with PG
cellulose with THBP
Fig. 4. Relationship between the weight average polymerization degree (DPw) and aging time of cellulose,
cellulose with antioxidant (EQ, PG, THBP) aged in 130ºC in nitrogen atmosphere
Results of thermal aging of cellulose in nitrogen atmosphere in 130ºC (Fig. 4) indicate
that antioxidant addition (EQ, PG, THBP) to cellulose matrix does not cause significant
changes in degradation of cellulose. Probably, in this high temperature, synthetic antioxidants
are less stable and rapidly undergo decomposition or evaporation, so their stabilizing activity
is much worse.
CONCLUSIONS
On the basis of the performed studies following conclusions can be drawn:
1. Antioxidant addition – 0.2% (EQ, PG, THBP) to cellulose matrix considerably reduces
the weight average polymerization degree of cellulose during thermal aging (130ºC) in
air atmosphere. Also the presence of low molecular substances (extractives) accelerates
thermal degradation of cellulose.