io A WATER-RESISTANT ANIMAE GELE SCHfiSL OF FORESTRY UBMH \ UNIVERSITY OF FLORIDA No. R4C UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin A WATER-RESISTANT ANIMAL GLUE By F. L. BROWNE, Senior Chemist The Forest Products Laboratory has found that it is practicable to give ordinary animal glue a fairly high degree of water-resistance by in- corporating certain chemicals with it just before application. A detailed description of the experiments was published in Industrial & Engineering Chemistry, Vol.19, p. 215, February 1927. The formula herein described has given very excellent results on the laboratory scale and is believed suit- able for certain types of manufacturing operations. In a typical test with three-ply panels of l/l6-inch birch veneer, average shearing strengths of ^75 pounds per square inch when dry and 165 pounds per square inch after soaking in water for 2 days were obtained. This is within the range of values shown by good water-resistant casein glues. The Formula Animal glue 100 parts by weight Water- 225 parts by weight Oxalic acid 5o parts by weight Paraformaldehyde... 10 parts by weight The glue is soaked in the cold water until the granules or flakes have been softened. It is then melted at about lU0° F. after which the temperature is allowed to fall to between 105° and II5 P. Die oxalic acid, in small crystals, and the paraformaldehyde (a fine, white powder) are then mixed together and added to the glue. The mixture is stirred until all of the oxalic acid has gone into solution, after which it is ready for use. Another good procedure is to soak and melt the glue in 200 parts of water, saving the other 25 parts to moisten the paraform- aldehyde and oxalic acid before adding them to the glue solution. Any tendency for the paraformaldehyde to form dry lumps when incorporated in the glue is thereby eliminated. Precautions in Using the Glue At a given temperature the addition of the oxalic acid and para- formaldehyde lowers the viscosity of the glue slightly. 3ut the new glue is used at lower temperatures than are customarily employed for animal glue so that the difference in viscosity brought about by the added in- gredients is compensated for by the effect of the lower temperatures at 1 "The proportion of water will depend upon the grade of glue employed and the viscosity of solution desired. In general, the proportion will be the same as would be employed when using the glue in question without addition of chemicals. RUO which it is used. It will "be understood, of course, that the water content may he altered at will to give a glue of any desired viscosity or to suit the requirements of different grades of animal glue. Care must he taken to keep the glue within the proper range of temperature. At a temperature between 105 c and 115" ?. and when using the • . er type of paraformaldehyde, the glue will remain in a fluid condition for 6 to 8 hours from the time of incorporating the paraform- aldehyde and oxalic acid, after which it will set to a tough, firm jelly which cannot he melted again. It is important to avoid heating i'.-.p glue mixture above 11^" if a long working life is required. At 12C ' the working life is 5 to 6 hours and at lUO c it is only 2-1/2 to 3 hours. Hie working life does not seem to differ materially with animal glues of widely varying grade. . lov: temperatures advised can he employed without danger of decomposition of the glue through bacterial action because paraformalde- hyde is an excellent antiseptic. Because of this lower temperature and the lower gel-point caused by the added chemicals, a slightly longer assembly period may be allowed in the gluing operation.? than would OTdinarily be employed with the grade of animal glue used. paraformaldehyde does not dissolve in the glue at once, "out most of it remains suspended as a finely divided solid during the. wor - ing life of the glue. A certain amount of agitation is therefore neces- sary to keep it evenly distributed throughout the mixture, preventing its settling to the bottom of the container. The paraformaldehyde used should be a fine enough powder to pass completely through a ^0~mer-,Y. sieve, in which case the amount of agitation provided "oy the mechanical glue spreader is sufficient 10 keep the paraformaldehyde stirred up. Tin glue should be stirred thoroughly in the mixer just before taki. it to the spreader or to bench glue pots. It is also important to use up a batch of glue and clean the Treading machinery and glue pot before the glue sets to a jelly because the tough, insoluble jelly is not easy to remove. Type of Paraformaldehyde to Use Commercial paraformaldehyde varies materially in certain of its properties, notably in its chemical reactivity. VThen used in this formula, some types of paraformaldehyde cause the glue to set to an unworkal jelly in a much shorter period of time than the working life as stated above. For example, glues were made uj in accordance with the formula usin# paraformaldehyde from five different factories and the range in working life at 115° was found to be as follows: P.UO _ 2 . Source of paraformaldehyde Factory number 1 2 3 k 5 Working life of glue Hours e.5 5 3 2.75 2.5 By heating a fast-reacting paraformaldehyde in a closed container at 212° for several days it can be made slow-reacting. The chemical re- activity, however, is subject to control during the manufacture of the paraformaldehyde and two companies have stated that they are able to furnish on order a type suitable for use in this formula. Their names will be supplied on request. Presumably other paraformaldehyde manu- facturers can also if specially requested. Influence of Grade of Glue When glues of different grade are employed in this formula it is necessary to vary the amount of water used in order to maintain the same viscosity of the glue solution, just as would be the case in employing the glues without addition of chemicals. Aside from this, different animal glues give approximately the same results. Such small differ- ences in working life, joint strength, and water-resistance as are ob- served with individual animal glues seem to be more or less independent of the glue grade measured in terms of viscosity and jelly strength as the following results show: Grade of glue— : Plywood tests : Joint test Work in™ Viscosity : Jelly strength • life Pry Wet Lbs. per sq. in. Wood failure Millipoises Grams 372 Hours 7 Lb s . pei ■ sq.in. 3.560 Percent US : kks 139 31 95 : 299 7-1A : 1463 : I63 3,600 : 36 76 : 2U0 6-l/U US2 ' 155 3.3S5 38 65 ' 190 7 — — 55 131 7 hhs ■ 113 3,720 39 — 'Glue grade measurements were made by the methods of the National Asso- ciation of Glue Manufacturers. Indus. Eng, Chem. 16, 3^0, 192-k Water-Resistance Levelops Slowly Test panels for determining the degree of water-resistance of this formu3a should be seasoned after gluing for at least 10 days before subjecting them to the soaking test because the full degree of rUo -3- water-resistance is developed slowly. A number of panels were made up with a single batch of glue and seasoned for varying lengths of time before testing, with the following results: lays seasoning Plywood test, wet Lbs. per sq. in. 2 20 3 65 5 95 7 115 9 lUO 10 150 12 ll+5 17 155 It should also be noted that the water-resistance of glues made by this formula is comparable with that of casein glues 7/hen the soak- ing test is carried out in water at ordinary room temperatures or less, "but in water at higher temperatures the values obtained in the test on the paraformaldehyde animal glue decrease with increasing temperatures. Thus, a series of tests gave the f ollo'..'in?: data: Lbs .per sq. in. Specimens tested dry... kos Specimens tested wet after 2 days' soaking in water at: 59° P, ... 77~ F. ... 95° F. ... 113 P. ... 1U0 C F. ... lgg 17^ 138 3k Other Chemicals that may be Used Both oxalic acid and paraformaldehyde are poisonous materials . Frocer precautions should be taken to see that they are not invested by m en usin-s; them . The oxalic acid can be replaced oy an equal weight of the nonpoisonous mucic acid. Any acid will serve to extend the worki:. life to a satisfactory period, but many of them affect either the dry strength or the water resistance adversely. There are a number of other substances that can be used in place of paraformaldehyde, but they all give off formaldehyde in the glue and are therefore just as objectionable from the point of view of poisonousness as paraformaldehyde. Further de- tails regarding them will be found in the reference previously cited. There is no detectable odor of formaldehyde in panels glued with this formula. hUo -4- UNIVtKSMY OF FLORIDA ii [ nun I! ii ii 3 1262 08923 8389 This glue may prove of value where high water-resistance is desirable and where other glues are not suitable for one reason or another. It is not alkaline and will not stain thin veneers. There is no reason to suppose that it will dull wood-working tools to any greater extent than ordinary animal glue. Persons contemplating trying out this formula should communi- cate with the Forest Froducts Laboratory, Madison, Wis., if they wish its suggestions in adapting the process to their special requirements. RUG -5-