Ind. Eng. Chem. Prod. Res. Dev. 1985, 24, 176-177
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COMMUNICATIONS Identiflcation of Thermosetting Adhesive Resins from Whey Permeate as High Molecular Weight Maillard Polymers The disposal of 23 billion pounds of excess whey (containing 5% lactose, 0.9% protein, and traces of salt) amounting to more than a billion pounds of whey solids derived from the cheese industry represents a serious economic and environmental problem due to high BOD (32000-60 000 mg/L). The advent of ultrafiltration techniques that separate the proteins from whey results in large quantities of permeate with essentially the same lactose content and exacerbates the disposal problem. Maillard and caramelization reactions associated with the thermal polymerization of reducing sugars were exploited to convert the lactose in whey to a thermosetting resin which proved to be an excellent adhesive for binding sdii lignocellulosicmaterials. Tailoring of the resin was possible by the addition of condensing agents such as urea and/or phenol to produce concentrated solutions of variable viscosity and pH. The proposed utilizationof whey byproducts in this manner would favor replacement of formaldehyde-based resins currently used in the forest product building board industry in addition to conserving nonrenewable energy resources in the form of petroleum and natural gas.
The disposal of more than 1.1 billion pounds of dry solids, from whey and whey permeate (containing 5% lactose and 170salts) derived from the cheese industry in the US.annually represents a serious economic and environmental problem due to high BOD (32000-60000 mg/L) and salts. Coincidentally, formaldehyde used in forest products building materials has created a potential public health problem. Caramelization reactions associated with the thermal polymerization of reducing sugars were exploited to convert lactose in whey to a thermosetting resin in aqueous solution of high solid content, devoid of formaldehyde, which proved to be an excellent adhesive for binding solid lignocellulosicmaterials. Tailoring of the resin was possibly by the addition of condensing agents, urea and/or phenol, to produce concentrated solutions of variable viscosity and pH. Ammonium nitrate was used as the acid catalyst to catalyze transformation of lactose to polymeric compounds and was kept at 8% (wt/wt of final solution) because this amount was found to be sufficient to produce a final pH of 2 to 3 when whey permeate containing the lactose was heated with the salt to yield an insoluble polymer at this pH range. A pH of 2.0 or less is considered undesirable as adhesive resins for wood,due to deterioration of the final
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Figure 1. pH profile of the reaction. Whey permeate in the presence of ammonium nitrate (8% w t j w t of the final solution) and urea and phenol a t different molar concentrations. Reaction mixture with 74% total solids, heated to 125 “C Aliquots withdrawn a t timed intervals. Curve I: lactose-urea-phenol; molar ratio: 1.00.5:0.5; curve 11: as I except lactose-urea-phenol; molar ratio. 1.0:0.5.1.0; curve 111. as I except lactose-urea-phenol: molar ratio: 1.0:1.0:0.5 0196-4321/85/1224-0176$01.50/0
physical properties of the bonded lignocellulose. Minor amounts of copper salt, e.g. CuC12,CuSO,, etc., were added to catalyze Maillard reactions known to result in high molecular weight heterocyclic polymers. The pH profile of the reaction using ammonium nitrate as the acid catalyst for transformation of permeate solids to polymeric resins in the presence of urea and phenol blend as condensing agents is shown in Figure 1. Viscosity value is an important factor that governs the type of application of the resin. Figures 2 and 3 show the 0 1985 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 1, 1985
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Figure 3. Change in viscosity as a function of reaction time. Viscosity values plotted are for 74% total solids content. Curves I through 111: same molar ratios as in Figure 1; curve IV whey permeate and urea (equimolar with respect to lactose and urea) with ammonium nitrate (8% wt/wt in final solution); 74% total solids, heated to 125 "C and aliquots withdrawn a t designated time intervals.
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not appear. However, when urea is present in the reaction mixture such a phenomenon is observed (Figure 3). We thus have a system where the pH and viscosity of the reaction mixture may be controlled to the required extent by varying the concentration of urea and phenol, by making use of curves such as those in Figures 2 and 3. The proposed structure of polymers resulting from lactose degradation and polymerization are analogous to proteins, because high molecular weight linear polymers with a large number of carbonyls would be expected to form on the condensation of urea with monomers. Proteins were therefore used as standards and a plot of elution volume vs. log (mol wt) served as a standard curve for estimating molecular weights of unknowns. Figure 4 shows the elution profile of a whey permeate polymer which is CH30H-insolublebut water-soluble. In general, CH,OHinsoluble but water-soluble polymers obtained from permeate containing lactose in the absence or presence of condensing agents, viz., urea and/or phenol, have a molecular weight in the range of 10000 to 80 000. A qualitative test was done to determine if free sugars are being incorporated into the methanol-insoluble polymers. The methanol-insoluble fraction was hydrolyzed in a sealed tube at 100 "C for 3 h with 6N HC1. The hydrolysate was freed from HC1 by evaporation under reduced pressure. Paper chromatography using anilinephthalate spray reagent and 1-propanol-EtOAc-water (7:1:2 v/v/v) as the solvent mixture showed the presence of a mixture of carbohydrate including glucose, galactose, and mannose, among others. The results are in agreement with the constituents of colorants in cane sugars refiner's final molasses. To the author's knowledge, this is the first instance for the synthesis of whey-based polymers as adhesives for lignocellulosic materials and their identification as compounds being generated by advanced Maillard reactions among others. Evaluation of the resins in terms of rate and temperature of cure and their adhesive strength characteristics shows them to be comparable to formaldehyde-containing resins, and the results will be published at a later date.
Acknowledgment
Figure 4. Elution profile of CH30H-insoluble-H20-solublecolarant on Sephadex G-100 column. Using Tris-HC1 buffer, pH 7.5 containing 0.1 M KC1 as eluent, at a flow rate of 36 mL/h. Polymer obtained from the reaction of whey permeate-NH4N03-urea (equimolar with respect to lactose and urea) and NH4N03at 8% w/w final solution, 74% total solids, heated to 125 O C for 120 min.
change in viscosity of the reaction mixture as a function of reaction time. As Figure 2 shows, in the case of reaction mixture where only whey permeate or permeate in presence of phenol is present, the viscosity goes down to a minimum prior to formation of insoluble solids. A smooth transition to higher viscosity followed by solidification does
This research was supported by the Cheese Research Institute, the University-Industry Research Program of the Graduate School and the College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI 53706. Although the research described in this article has been funded in part by the United States Environmental Protection Agency through Contract No. 68-02-4043 to Chemical Process Corp., Brookfield, WI, it has not been subject to the Agency's peer and administrative review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. The author also wishes to acknowledge helpful comments by Dr. Tom Richardson. Registry No. Lactose homopolymer, 37383-89-4; (lactose). (phenol)(copolymer), 93862-39-6; (lactose).(urea) copolymer, 93862-40-9. Department of Chemistry University of Arkansas Little Rock, Arkansas 72204
Tito Viswanathan
Received for review September 10, 1984 Accepted October 16, 1984
