## 4 Conclusions  
This study employed the Fenton oxidation reaction under heterogeneous conditions for the treatment of flax fibers (FFs). The results showed that treatment under the desired concentrations (10 wt.% H\({}_{2}\)O\({}_{2}\) and 2 wt.% FeO\({}_{4}\)) in water at neutral conditions (pH -7) for 15 h resulted in fibers with a reduced size distribution with a lower average fiber diameter, as compared with untreated fibers. The results reveal that the Fenton AOR process under heterogeneous conditions offers a sustainable approach for the pretreatment of biomass FFs to yield biomass with enriched cellulose content. As well, modified FFs showed a 60% reduction in average fiber diameter from 12.3 \(\pm\) 0.5 \(\upmu\)m to 5.2 \(\pm\) 0.3 \(\upmu\)m. Thus, the Fenton AOR process can selectively remove the non-cellulosic content (e.g., hemicellulose, lignin, etc.) of FFs in an effective manner. This trend was attributed to the higher affinity of the biomass fractions toward ferrous species, as compared with pure cellulose. The study found that the use of traditional techniques, such as alkali treatment, was less effective for the removal of non-cellulosic content versus the Fenton AOR method. The combined use of alkali treatment with the Fenton AOR process did not significantly decrease the average diameter of FFs, as compared to the Fenton AOR process without alkali. Based on these results, the Fenton AOR process is an effective technique for producing cellulosic microfibrils in FFs, as compared with harsh alkali treatment methods. The effective removal of the non-cellulose components for the treated fibers showed a measurable reduction in MB dye adsorption versus the pristine flax fibers, which are known to contain a higher lignocellulosic content. This is attributed to the role of structural alteration of FFs and/or chemical removal of non-cellulose components with the Fenton AOR method. Despite its known effectiveness in homogenous media, chemical treatment of natural fibers under heterogeneous conditions was demonstrated. The AOR process for the reduction of fiber diameter of flax reveals its potential utility in synthetic fiber modification. Various technological applications of modified fibers include advanced polymer-fiber composites, fiber carriers for drug delivery, biomedical devices, advanced filtration, and adsorbent media [40; 46].  
Conceptualization, L.D.W.; methodology, N.A.; formal analysis, N.A.; writing--original draft preparation, N.A.; writing--review and editing, N.A., L.D.W. and D.E.C.; supervision, L.D.W. and D.E.C.; project administration, L.D.W.; funding acquisition, L.D.W. All authors have read and agreed to the published version of the manuscript.  
acknowledges the support provided by the Government of Canada through the Government of Saskatchewan (Ministry of Agriculture) Agriculture Development Fund (Project #: 20200408) for support of this research.  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
[PERSON] is acknowledged for technical support with the collection of X-ray photoelectron spectra of fiber samples. [PERSON] of Biolin Research Ltd. is acknowledged for helpful discussions during this research project. The authors wish to make a land acknowledgment that this work was carried out in Treaty 6 Territory and the Homeland of the Metis. As such, we pay our respect to the First Nations and Metis ancestors of this place and reaffirm our relationship with one another.  
The authors declare no conflicts of interest.