Effect of acid value on the esterification mechanism of maleinized soybean oil with cotton.
Keywords Anhydride group, Amide group, Cellulose, Cotton, Infrared spectroscopy, Soybean oil
Molecular crosslinker 1,2-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) is used in the commercial treatment of cotton textiles for wrinkle resistance. In the interest of formaldehyde-free alternatives to DMDHEU, polycarboxylic acids that can form 2-3 anhydride groups upon high-temperature curing have been investigated as cellulose crosslinkers. (1-4) Maleinized soybean oil (MSO) was synthesized to behave as a biobased crosslinker that is capable of forming multiple anhydride intermediates, which could subsequently react with cellulose hydroxyl groups. (5), (6) In comparison with small molecule polycarboxylic acids, the molecular spacing between diacid groups is considerably larger. Further, MSO is neutralized with excess ammonium hydroxide to promote its solubility in water.
Noteworthy wrinkle resistance was demonstrated by cotton fabrics treated with aqueous ammonia-neutralized MSO (NMSO). Although NMSO-2 (having approximately two anhydride moieties per triglyceride) exhibited lower wrinkle recovery angles (WRAs) and smoothness appearance ratings relative to glycolated DMDHEU, the mild improvement in cotton's wrinkle recovery has motivated the evaluation of MSO-3 (having approximately three anhydride moieties per triglyceride) (5) and the spectroscopic study of these maleinized triglycerides. The aqueous treatment of 3.3 weight percent (wt%) NMSO-3 resulted in WRA values that were comparable with the treatment of 3.6 wt% glycolated DMDHEU (285 vs 277), higher tensile strength retention (94% vs 52%), but lower smoothness ratings upon laundering (2 vs 3). (5) The unique behavior of MSO reagents in comparison to glycolated DMDHEU was therefore attributed to their molecular weight, flexibility, and crosslinks with cellulose. (5)
Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis has been used to characterize the reaction of polycarboxylic acid reagents with cellulosc. (3), (4) In particular, the retention of MSO-2 and MSO-3, as quantified by the 1744 [cm.sup.-1] IR absorbance peak for triglyceride esters onto fabrics that were heat cured and washed was observed to increase with increasing NMSO content in the treatment bath. (5) The properties of wrinkle recovery and retention were suggestive of crosslinking between MSO and cellulose. (5)
In this study, DRIFTS was used to delineate the effects of MSO acid value on the reaction mechanisms of NMSO with cellulose. IR peaks in the ranges of 1700 and 1740 [cm.sup.-1] were examined to differentiate absorbance peaks due to cellulose esterification from those indicative of triglyceride esters, carboxylic acids, and amide carbonyl groups (per the reaction of diacids in the presence of ammonium hydroxide (7)).
Experimental methods and materials
MSO solution baths
MSO-2 and MSO-3 each had acid values of 156 and 230 mg KOH/mg, respectively. The synthesis of MSO has been described in Johnson et al. (5) NMSO was prepared by blending 53 wt% MSO with 47 wt% ammonium hydroxide (29% assay, Fisher Scientific). MSO-2 and MSO-3 were neutralized with 11 and 7.6 mol of aqueous ammonia per anhydride, respectively. Desized, bleached cotton, and mercerized cotton (styles # 400 and 400 M obtained from Testfabrics, Inc.) were treated with NMSO diluted with deionized water. Mercerized cotton in this study does not wholly consist of cellulose II. (8) Therefore, mercerization will refer to the commercial treatment of the cotton fabric with sodium hydroxide. The wet pick-up (9) of finished sheets averaged 92% for MSO-2 and 85% for MSO-3. Treated sheets at various levels of MSO in the bath were initially dried at 80[degrees]C for 6 min followed by curing for 4 min at 160[degrees]C.
Samples were laundered and/or soaked in ammonium hydroxide for 4 min to aid in removal of the unreacted MSO. Samples were washed in a 20 lb Speed Queen washer-extractor with 38.5 g of American Association of Textile Chemists and Colorists (AATCC) standard liquid detergent in 10 gallons of water at ~47[degrees]C. All the samples were dried at 50[degrees]C. Sample specimens were prepared using a BioRad diffuse reflectance attachment in combination with the IR spectrometer. Potassium bromide was used as the IR background. The protocol for sample characterization involved the averaging of three spectra, each obtained at 128 scans with a resolution set to 4 [cm.sup.-1]. Spectral analysis was performed using a common baseline and peak heights normalized to the C-H bending peak at 1319 [cm.sup.-1]. (1), (3), (4)
Results and discussion
Analysis of MSO spectra
NMSO-2- and NMSO-3-treated cotton have been shown to react with cellulose through different reaction mechanisms. Reaction schemes described within Fig. 1 correlate the conversion of reactive species with heat treatments. Infrared spectra of fabrics treated with NMSO-2 dried at 80[degrees]C and cured at 160[degrees]C are shown in Figs. 2i and 2ii, respectively. Treatments of NMSO and aqueous ammonia shifted the peaks indicative of absorbed water from 1641 to 1666 [cm.sup.1] (Fig. 2. The characteristic peaks of MSO cyclic anhydrides (1788 and 1861 [cm.sup.1]) were eliminated upon rinsing with aqueous ammonia (Fig. 2i). Carboxylic acid absorbance was identified at ~1715 [cm.sup.1] as shown in Fig. 2i-b,c and 2ii-b.c. Spectral absorbance at 1715 [cm.sup.1] (Fig. 2i-c) among rinsed MSO-2-treated fabrics implies the presence of free acids that did not react with ammonium hydroxide. It is possible for the fatty acid hydrophobes to reduce the accessibility of ammonium hydroxide to MSO-2 and MSO-3 free acids. Figure 2ii-b,c spectra of MSO-2-treated cotton reveals an absorbance shoulder between the 1715 [cm.sup.-1](carboxylic acid absorbance) and 1744 [cm.sup.-1] (triglyceride ester absorbance) peaks. Scrutiny of this region (Fig. 2ii-b,c) reveals an absorbance spike at 1722 [cm.sup.1] that is attributed to cellulose esterification via the anhydride functionalities (3-5), (9), (10) of MSO-2.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
The IR spectra of mercerized and unmercerized cotton treated with 3-12.1 wt% MSO-3, dried, cured, laundered, and rinsed with ammonium hydroxide were similar and are represented by Fig. 3. Interestingly, the spectra in Fig. 3 was similar to Fig. 2ii-b,c of MSO-2-treated cotton in terms of having an absorbance spike at 1722 [cm.sup.-1]. Therefore, cellulose esterification was confirmed among NMSO-2-and NMSO-3-treated fabrics. However, absorbance, spikes at 1709 and 1726 [cm.sup.-1] of Fig. 3 were unique to NMSO-3-treated cotton and mercerized cotton fabrics.
[FIGURE 3 OMITTED]
The absorbance spikes at 1709 [cm.sup.-1] (in Fig. 3) were attributed to acylation of ammonia by free carboxylic acids (7) and proton transfer to the basic nitrogen. (11) Ford et al. observed in situ synthesis of amide functional MSO-2 among cotton fabrics treated with aqueous ethanolamine NMSO-2. (6) Amidation, which arose from condensation reactions between carhoxylate salts of ethanolamine, was confirmed by the appearance of an amide carbonyl peak at 1705 [cm.sup.-1]. (6) The frequency of amide absorbance was influenced by proton transfer (11) from the neighboring carboxylic acid to the ethanolamide functionality. (6)
DRIFT'S analysis of maleamic acid-treated fabrics confirmed the formation of ester linkages via protonated amide functional groups at 160[degrees]C. (6) Absorbance spikes at 1722 and 1726 [cm.sup.-1] among the spectra of NMS0-3-treated fabrics (Fig. 3) were therefore attributed to cellulose reaction per anhydrides and amides, (6), (12) as represented within Fig. 1. The alcoholysis of primary carboxamides has been reported to proceed in the presence of acidic catalysts (7), (13) or via carboximidamide intermediates. (14) Further evidence of cellulose half-acid ester products, as a result of aqueous malcamic acid reaction with cellulose, has been reported by Cuculo (12) and in Ford et al. (6)
Ammonium hydroxide NMSO is a formaldehyde-free, macromolecule which is capable of crosslinking cellulose. Owing to the porous nature of these fabrics, we can speculate DRIFTS to penetrate the surfaces of at least two sheets of fabric (that are each 150 [micro]m thick). Based on the WAXD analysis of NMSO-treated fabrics, (8) IR must reveal NMSO reactions within the crystalline and amorphous regions of cotton cellulose. Further, DRIFTS analysis facilitated detection of ester groups: produced via reaction of cyclic anhydride and protonated amide intermediates with cellulose hydroxyl groups. The reaction pathways of ammonium hydroxide NMSO with cotton cellulose are influenced by the degree of triglyceride modification with diacid groups. The in situ amidation of aqueous ammonia NMSO upon curing was only evident among the trisubstituted soybean oil triglycerides (230 mg KOH/g), and not MSO-2 (156 mg KOH/g). Differences between the reaction mechanisms of aqueous ammonia NMSO-2 and NMSO-3 are presumably linked to their locales within the cellulose microstructure. Unlike NMSO-2, macromolecular NMSO-3 could penetrate the hydrophilic domains of crystalline cellulose upon fabric curing, according to Ford et al. (8); wherein, the protonated amide functional groups of MSO-3 reacted with cellulose hydroxyl groups.
Acknowledgments The authors gratefully acknowledge the support received from the Cooperative State Research Education and Extension Service, the U.S. Department of Agriculture, Agreement No. 2001-38202-10424. The authors also thank David Delatte for synthesizing the maleinized soybean oil investigated in this study.
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Oral Presentation at the American Chemical Society: Cellulose and Renewable Materials Division (Chicago, IL) March 28, 2007.
E. N. J. Ford *, J. W. Rawlins, S. K. Mendon, S. F. Thames
School of Polymers and High Performance Materials, The University of Southern Mississippi, 118 College Drive #5217, Hattiesburg, MS 39406, USA e-mail: firstname.lastname@example.org
J. W. Rawlins
[c] ACA and OCCA 2012
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|Title Annotation:||BRIEF COMMUNICATION|
|Author:||Ford, Ericka N.J.; Rawlins, James W.; Mendon, Sharathkumar K.; Thames, Shelby F.|
|Date:||Sep 1, 2012|
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