US2806825A - Asphaltic molding compositions and molded articles containing wood fiber - Google Patents

Description

tent:

2,806,825 Patented Sept. 17, 1957 ASPHALTEC MOLDENG COWGSITIONS AND MOLDED ARTICLES CGNTA INING WU'IED FIBER No Drawing. Application June 26, 1952, Serial No. 2%,820

Claims. (Cl. 269-?) The current art of manufacture of bituminous molded articles of acid-resistant character, e. g. storage battery cases, utilizes asphalt as a binder, an acid-resistant mineral matter such as talc as a hardness-imparting filler, and cotton linters as a fibrous toughening agent. By proper choice, proportioning and mixing of such ingredients storage battery cases can be made which meet the many and rigid physical tests now established for such articles, and which are acid-resistant in the sense that they stand up in the continued presence of acid solutions such as the sulfuric acid electrolyte of lead-acid accumulators. It was pointed out in the Lukens Patent 1,752,917 (now expired) that acid resistance could be attained in such molded articles if the quantity of organic fiber was kept below about by weight of the composition.

Molded articles of this class are subject to the peculiar phenomenon of acid penetration. While the composition is acid resistant in the sense above, any aqueous liquid including the storage battery electrolyte has a tendency gradually to penetrate into the walls of the molded article. The rate of penetration may, under certain circumstances, be so slow as not to interfere with the useful life of the article; but if, say in a partition between cells, the electrolyte acting from both sides should penetrate entirely through the wall section, an electrical path Will be established between the adjacent cells with consequent impairment of the efi'iciency of the storage battery. The precise mechanism of acid penetration is not known, since it does not appear to be explainable by reference alone to the wicking action of the fibers which, in properly molded structure, are not normally exposed at molded surfaces. It is customary in the great bulk of storage batteries made today to confine the total quantity of organic fiber present to about 11% by weight of the composition.

In Patent 2,501,995, Edward R. Dillehay taught a way of decreasing acid penetration by incorporating into the composition a small quantity of a synthetic resin capable of setting up to an acid-resistant state when catalyzed by the presence of acid. When the resin so incorporated persists in the molded article in an incompletely polymerized condition, the presence of acid against the walls results n the formation in situ of some sort of acid barrier. The walls, while retaining their penetrability by other aqueous liquids, show a greatly retarded penetrability by acids and acid solutions. Some penetrability by acid remains, however, in compositions in which the resin content is small; and it is a general rule that, with or without the resin, penetration will increase with increases in the fibrous content, though at different rates.

Cotton linters has hitherto been generally regarded as the only commercially important fibrous reinforcement for bituminous storage cases and similar uses. Many attempts have been made to use other fibers, animal, vegetable and mineral, but these have encountered difficulties, either in processing, in various aspects of economy, or in the qualities of the finished product.

Cotton linters has hitherto been an economically available fibrous reinforcement having a fairly uniform and advantageous fiber length in view of the nature of the fibers themselves. Nevertheless, difficulties are encountered iu the use of linters. The fiber is not always of uniform quality. It is frequently contaminated with undesirable foreign materials, and is often matted or otherwise in poor condition so that pretreatments are advisable. Such pretreatments require investment in machinery, and involve time delays. Moreover, cotton linters is currently becoming less readily available, and hence more costly to use.

One of the objects of the invention is the provision of new molded articles and modes of making them which eliminate cotton in whole or in part as a fibrous reinforcement.

Another object of the invention is the provision of molded articles of the classes to which this specification pertains, which articles have improved physical properties and lessened acid penetration, and the provision of modes of making them.

Yet another object of the invention is the attainment of economic and processing advantages in the production of such molded articles.

These and other objects of the invention, which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, I accomplish by those procedures and in those compositions and molded articles of which I shall now describe certain exemplary embodiments.

I have found that a certain class of fibers derived from wood possesses some new and unexpected properties when employed in compositions of the classes to which this invention relates. It is not practicable, however, merely to substitute these fibers for cotton in compositions otherwise identical. Rather, the successful use of these fibers depends upon the utilization of their unexpected properties in ways which will hereinafter be fully explained.

First, by Way of definition of the class of fiber to which I refer, the current term in the art is exploded wood fiber. Such fiber is prepared by placing green wood chips or shreds in an atmosphere of steam under pressure in a suitable vessel, and then rapidly releasing the pressure, whereupon the substantially instantaneous evaporation of water from the chips or shreds causes them to explode and fiberize. Such a procedure is well recognized in the art, and fibers produced in this fashion are widely used in the manufacture of insulation, Wallboard, hard board and the like. Neither the wood nor the resultant fiber are ordinarily subjected to any chemical treatment, and none is necessary for my purposes. While some chemical treatment may be practiced without departing from the spirit of this invention, I do not contemplate such digestion or other chemical treatment as would essentially change the nature of the fibre, nor destroy the general and recognized character of the fibrous product as exploded wood fibre as understood in the art, and as can be seen under the microscope.

Not all exploded wood fiber is identical, nor do all available exploded wood fibers are for the most part alder, 1

cottonwood, Douglas fir, and hemlock.

Hereinafter for convenience I shall use the term exploded wood for the fiber. Also, although the term filler is frequently used to cover all of the ingredients storage battery cases'current in the art is the following:

. Percent Asphalt 46.2 Talc 40.0 Cotton linters 11.0 Acid-catalyzable .resin 2.8

the; percentages being by weight.

Where: the asphalt is properly chosen (andin this connection reference is made to the Dillehay Patent 2,501,- 995 )-and the ingredient properly mixed and molded, successful storage battery casesmay be made meeting all of the; physical'and electrical tests current in the art.

The substitution of an equivalent weight of exploded wood for the cotton linters in the above formula will result in an immediate and serious loss in impact resistance, in a conventional test performed by subjecting the wall of a molded article to repeated blows from a standard falling or swinging object. Also, there will be losses in tensile strength and elongation under standard tests. Containers so produced are not of commercial interest by todays standards.

I have ascertained, however, that bituminous compositions made on the above formula with exploded'wood had exceptionally low acid absorpt ion values as compared with the composition containing cotton. Acid absorption tests are conducted by immersing samples cut from the walls of molded containers in storage battery electrolyte under standardized conditions for varying lengths of time and ascertaining the actual absorption of the electrolyte by the samples on a weight percentage basis. The tests give an indication of penetration. The use of an incompletely polymerized, acid-catalyzable. resin in building up an acid barrier and in retarding the rate of acid penetration has been noted hereinabove. The specific effect will vary with the total quantity of resin in the article, which in turn involves economic considerations; but with minute quantities of resin as in the above formula, the effect ismost pronounced. on molded surfaces. Where the samples have cut surfaces of large area, as in the described test,

where the contained fibers are exposed, cotton compositions. show a greatly retarded acid absorptionbut nevertheless an absorption which is progressive with elapsed time, with small amounts of resin. For example, samples from a. cotton composition tested for 106 days showed an absorption of about 3% at the end of that time, the absorption curve indicating that the absorption was still increasing.

By contrast, samples from a composition in which e ploded wood was substituted in equal quantity for the cotton in the above formula (the resin content remaining the same) showed an absorption of about .6% at the end of about 28 days, after which the absorption did not significantly increase to the end of the l06 '-day span of the test period. In other words, the curve representing absorption values as against time became asymptotic toa maximum absorption value irrespective of the fact that the samples also had the usual cut-surfaces. At a later periodit was ascertained that this was a characteristic behavior of asphalt-resin-exploded woodcompositions within rather wide limits of formula. Compositions containing different quantities of exploded wood show different maximum absorption values; but the various curves tend to become asymptotic to these values. Thusexplodedwood appears to coact with resin-blended 4 bitumen in a way which is not identical with the coaction of cotton.

As a consequence, work was started in an endeavor to improve the physical properties of asphaltic compositions containing exploded wood while maintaining the acid properties equal to or superior to those of cotton compositions. It was found that this was possible, because with an increase in the content of exploded wood, the impact and tensile values rapidly improved while the acid absorption, and in particular the long-time acid absorption, did not greatly increase. By way of a single example, acid absorption samples of a composition containing about 14 /2 of exploded wood by weight showed an acid absorption of about 1.4% and were not increasing at the end of the 106-day test period, whereas as before mentioned, a composition containing 11% of cotton fibers had reached an acid absorption value of about 3% in the same length of time and was still increasing in acid absorption. An increase in the percentage of fibrous reinforcement in a bituminous composition could be expected to raise the impact value; but so far as I know, the combined properties of good impact and resistance to acid absorption are peculiar to exploded wood fibers, and do not hold true for any other fibers of organic origin of which I am aware- Thus, with papermakers fiber, if the fiber ratio is raised to improve impact, this must'be done at the sacrifice of acid resistance which already is no better than that of cotton on an equal weight basis, and at the same low resin content of the composition.

'In increasing the amount of fibrous reinforcement in v a given composition, this should not be done haphazardly, or at the expense of the binder. As fiber ratios are increased, th eamount of mineral filler should be reduced. This can be done and is frequently done on the basis'of experience; but it is entirely possible otherwise to arrive at proportions which will give the maximum strength and impact resistance from the materials involved. By way of example, if some particular fibrous material is mixed with an asphaltic binder in varying proportions, it will be found that some particular proportion gives the greatest strength and impact resistance. The exact proportion will vary somewhat with different binders, and more importantly with different fibrous materials. With any given ingredients, the composition of utmost strength and impact resistance may be called composition A. Similarly, a

Using an exemplary binder having a melting point of 290 to 300 F. anda penetration between 16 and 22, in.

accordance with A.S.T.M. standards, at a temperature of 150 F., under a load of gms. applied-for a time of 5 seconds, it was found (a) that for every part of exploded wood fibre from 2 to 2.2.parts by weight of the binder was required to give maximum tensile strength and impact resistance, and (b) for every part of talc there was required about 0.49 part of the binder by weight to give maximum physical properties.

Assume a composition were desired containing 11% fibre. The fibre would itself require 22% of the binder. Adding, say, 3% for the resin, we now have a total of 36% or 36 parts by weight. The diiference between this and 100% (namely 64% or 64 parts) is the asphalttalc mixture making up the balance of the composition, the talc-asphalt ratio being 1:0.49' as set forth above. This does not mean that actual binder fi'bre and binderfiller mixtures must be; made and blended. together, al-

mixture above figures at about 41.5 parts talcand 22.5

asse ses I II 111 Percent Percent Percent Binder (asphalt and resin). 45. 5 51.0 58.0 Exploded W'ood Fibre 9.0 15.0 22.0 Talc 45. 5 34. 20. 0

As had already been indicated, a composition containing only 9% of exploded wood fiber as its sole fibrous ingredient will be deficient in impact value, although showing a very low absorptivity for acid. Using conventional asphaltic binders, such as the one noted above, it is usually necessary to increase the quantity of exploded wood fiber to about 13% to equal the impact value obtainable with about 11% of a good grade of cotton linters. At a content of 13% exploded wood fiber, however, the acid penetration of the composition is still superior to that of the cotton composition; and it has been my experience that in a composition containing 2.8% resin, the quantity of exploded wood fiber can be increased to about 16% while retaining an absorptivity for acid equal or superior to that of an 11% cotton composition. Such an increase, of course, gives measurably improved impact values.

conservatively speaking 14% of exploded wood will give at most as low an acid absorption value as 11% of cotton, and 11% of exploded wood will give at most as low an acid absorption value as 8% to 9% of cotton, with or without resin. Without attempting to set an upper limit on acid absorption, it may be pointed out that acid absorption can be diminished by increasing the resin content of the composition, taking into account economic considerations. The acid absorption of a composition containing as much as 25 exploded Wood fiber and resin is not significantly greater than the absorption of a composition containing 13% of exploded wood fibre and about 2.8% or 3% resin.

Generally, I teach compositions containing substantially 13% to 25% exploded wood fibre (where this is the sole fibrous ingredient), and substantially 40 to 13% filler (such as talc or equivalent), the balance being bituminous binder plus small amounts of resin, and/ or son e modification agent such as rubber hydrocarbon.

It was also observed that the penetration of plastic bituminous compositions containing exploded wood fibers, i. e. the stiffness or viscosity of such compositions at given temperatures, as well as the bulge test results on articles molded therefrom, tended to be well below specifications and well below the values given by comparable amounts of cotton linters in similar compositions. Therefore, it was reasoned that a somewhat softer binder could be employed both to improve mixing conditions and to increase the impact resistance without resulting in a molded article having an excessive tendency to bulge under given strains and temperatures. This is a factor which, so far as i know, is 850 unique to exploded wood. It will be understood that bulge resistance is improved by increasing the amount of fibrous reinforcement in a composition; but it is characteristic of exploded wood that the bulge resistances are so high on an equal percentage weight basis that a softer binder may readily be employed to incre se impact resistance as set forth. There is, naturally, a limit to the employment of softer binder substances, and I do not generally recommend a penetration of the composition lower than about 22. Such a penetration may be taken in the same way penetrations are taken of asphaltic binders alone, in accordance with the A. S. T. M. standards at a temperature of 150 F., under a load of 100 gms. applied for a time of 5 seconds.

Other advantages flow from the use of exploded wood in compositions and molded articles of this class. By way of example, Where the quantity of exploded wood is greater than the currently used quantities of cotton fiber in comparable articles, the specific gravity of the molded structure is less since the increase in fiber is taken at the expense of a heavier mineral filler. This makes the articles easier to handle, and less expensive to ship and store.

The exploded wood mixes well with the other ingredients of compositions of this class. The mixing procedures which I employ with exploded wood fibers do not differ from those hitherto used with cotton-containing compositions. Any of those mixing procedures which have been employed in the art may be used. For example, all ingredients may be introduced into a suitable power mixer together with water and mixed under heat to a state of homogeneity. The so-called quick-mix method is available. Here the liquid bituminous binder and the mineral filler are first commingled in a mixer, after which the fibrous material and water are added and rapidly incorporated with a lowering of the temperature. The composition is then preferably passed through one or more extrusion mixers of the masticator type. Yet again, the so-called dry-mix procedure may be followed in which the binder in powdered condition is mixed with the fiber, the filler, and appropriate quantities of the resin (liquid) and water to give an initial mix which is dry in the sense that it is a loose or powdery mass in spite of the presence of the liquids. This mass, which then may be further homogenized as by treatment in a Sprout-Waldron blender, is finally passed through one or more extrusion masticators, wherein it is both homogenized and plasticized. It is usual to add water to the composition in the masticators to keep the temperature down. I have noted that formulations utilizing exploded wood fibers generate more ,heat in the masticators so that it may be advisable to add more water to control the temperature. Otherwise, no difierences in processing or in molding are apparent. Compositions utilizing exploded wood fibers mold well and make molded articles having smooth and attractive surfaces.

A study was made of various exploded wood fibers and various fiber lengths of the same fiber to determine whether the generalizations given above are correct. Exploded wood fibers were classified as to fiber size in the following order: a +14 fraction, a +40 fraction, a +100 fraction, and a 1OO fraction. These size designations were determined using a Clark screen classifier.

The following table will indicate approximately the percentage composition of the various fractions:

[Percent retained on screen] Fraction +8 +24 +50 80 I found that the fiber length had little or no effect on the impact resistance of the molded article. However, a microscopic study of the molded articles revealed that the larger fractions did not mix in as well. On the basis of this study, I have in my own work eliminated the use of the +14 fraction, since it presents a danger of increasing apparent acid penetration and absorption through the exposure at molded surfaces of improperly mixed or improperly incorporated fibrous masses. The or smallest fraction does not increase the impact resistance of compositions proportionately as much as do the other fractions. For example, using equivalent quantities of the several fractions of exploded cottonwood fibers, it was found that the 1OO fraction gave an impact resistance of 6.3. The largest fraction, namely the V creases in the amount of resin present.

+14 fraction gave an impact resistancev of 7.6." The next largest or +40 fraction gave a slightly lower impact resistance of 7.3; but the best impact resistance was given bythe +100 fraction of this fiber, namely an impact resistance of 7.8.

As a consequence of these considerations, I prefer to use exploded wood fibers of fiber lengths as given for the +40 and +100 fractions in the table above.

As indicated above, exploded wood fibers from all wood sources, are'not identical, although they have. in comon the general characteristics, set forth above. Of the. Commonly available exploded wood fibers, I prefer cottonwood to the others which I rate. in the following order: alder, hemlock and Douglas fir. Weight for weight, the cottowood fiber appears to produce greater impact resistances in all fractions thanthe other. wood fibers mentioned, which vary among themselves in effectiveness in. the several fractions. By way of example, the +100 fraction of cottonwood in a given amount, gave an impact value of 7.8, whereas the same fraction and amount of alder gave a value of 6.1, hemlock giving a value of 5.0 and Douglas fir a value of 5.2.

The impact value of a cotton composition on the first formula given above, by the same test, was 5.7. When 11% of +100. cottonwood fiber was substituted for the 11% of cotton in an otherwise identical composition,-the

impact resistance was only 4.6 by. the test, a value too.

low to be commercially significant. When, however, the

quantity of cottonwood fiber in the composition was in-.

creased in accordance with the teachings above, to a Value of 14.4%, the impact value had risen to 6.7 by thesame test, which is definitely and markedly superiorto the im-. pact value of the comparable cotton composition. At this point, the acid absorption value of the exploded wood composition was less than half of that of the cotton composition, and had apparently attained a fixed value, whereas the acid absorption-of the cotton com position was. still increasing at the end of 106 days of test.

Larger quantities. of. exploded wood will still furtherincrease impact resistance, resistance to bulging, tensile strength and the like while retaining acid properties equal to or better than the acid properties of current cotton compositions, as has been set forth.

The resins which have been referred to hereinabove are those taughtin the Dillehay Patent- 2,501,995, namely acid polymeri'zable resins chosen from a class consisting of partially polymerized furfuryl alcohol, phenol-furfural, phenol-formaldehyde, and mixtures thereof. That patent suggested'the use of such resins in an amount substantially between 1 /2% and 30% by weight'of the total binder, i. e. the asphalt or bitumen plus the resin. Economical considerations among other things will determine the amount of resin which will ordinarily be employed. While I believe that the novel results which flow from the practice of my invention are in large part dependent upon a coaction between exploded wood fibers and the combination of binder and resin, I desire to point out that the use of exploded wood fibers enables me on the one hand to secure an equal or superior acid resistance with a smaller quantity of polymerizable resin present, and on the other hand, to vary or modify the specific acid absorption of exploded wood compositions containing any given amount of exploded wood fiber by increases or de- Thus it is readily possible, economic conditions permitting, to maintain the same ultimate acid absorption with an increased, amount of wood fiber by increasing the resin content of'the composition. This, of course, is within reasonable limits,

since the. resin, beingxa softer ingredient, tends to lower the stifiness and increase the penetration of any given bituminous binder, so that it is generally necessary tov compensate for'the softening effect .of' theresinby the employment of a harder binder as the resin quantityis increased.v Nevertheless as a generalrule, I prefer-to use an increase in the amount of resin with an increase in the amount of exploded wood as illustrated by'the following two exemplary formulae:

Wood Fiber ..percent. 14.0 11.0; Talc. V V V (10.-.- 34. 6 41: 0 Resin. -.do-..- 3.0 2.1 A sn'halt do 48. 4; p 45. 9

Test Cotton Exploded Linters Wood 2. 61 3. 0 7. 5 9. 0 1, 052 l, 240 Flnn atinn 1. 44 I. 13 Tensile X Elongation 1, 548 1, 411 Bulge:

Side 0.031 0. 015 End 0. 119 0. 0 34 FORMULATION USED Asphalt. 46. 2 47. 4 Talc. V 40. 0 35. 8 Fiber 11.0 14. O Resin 2. 8 2. 8

It will be noted that the exploded wood composition has a measurable advantage in specific gravity. Its composition penetration is less. It shows an advantage in both forms of the dropped ball impact test. It has. also a somewhat greater tensile strength. 'Its elongation value issornewhat less, but it is comparable in'this value and in'the product of tensile'and elongation with the cotton linters composition. It'shows a distinctly lessened re sponse to both formsv of the standard bulge test. Its acid absorption is markedly less, as indicated above. It will be seen that the exploded wood container is a distinctly superior product. The above figureswere taken from boxes produced in production runs.

My invention contemplates the use ofexploded wood fibers in whole or in part as the fibrous reinforcement in compositions and molded articles of the classes referred to. Exploded wood may be used as a partial or complete replacement for other types of fibers in such compositions and moldedarticles. Further, a percentage ofexploded wood may be employed in compositions of this. class to increase impact resistances without substantially lowering acid values where the percentage of other fibers also employed is. such as to give satisfactory acid'values. Thus, in a structure in which cotton is used, a part of the cotton may be substituted by exploded wood fibres,

permitting the use of a somewhat greater total quantity of fibrous reinforcement without sacrifice of acid qualities, or the attainment. of better acid qualitieswith equivalent physical properties. Similarly articles may be made with combinations. of papermakers fibre and exploded Wood fibre, as well as mixtures. of these with cotton or other fibres.

Modifications may be made in my invention without departing from the spirit of it: Having thus described my invention in certain exemplary embodiments, what l claim as new and desire to secure by Letters Patent is: I

1. An acid-resistant molding: composition comprising as a fibrous reinforcement substantially 13% to 25% of exploded Wood fiber and substantially 40% to 13% of non-fibrous, finely divided, acid-resistant filler, the balance being a bituminous binder.

- 2. An acid-resistant molding composition comprising substantially 13% to 25% of exploded wood fiber and substantially 40% to 13% of non-fibrous, finely divided,

acid-resistant filler, the balance being a bituminous binder, including a small quantity of an incompletely polymerized resin, acid polymerizable to an acid-resistant state, and chosen from a class consisting of partially polymerized furfuryl alcohol, phenol-furfural, phenol-formaldehyde and mixtures thereof.

3. The composition claimed in claim 1, wherein the quantity of non-fibrous filler varies inversely with the quantity of exploded wood fiber within the limits set forth.

4. The composition claimed in claim 2, wherein the quantity of non-fibrous filler varies inversely with the quantity of exploded wood fiber within the limits set forth, and in which the quantity of resin is substantially 0.5% to varying directly with the quantity of exploded wood fiber within the limits set forth.

5. A molded storage battery container made from the molding composition of claim 1.

6. A molded storage battery container made from the composition of claim 2.

7. A molded storage battery container of good acid properties and superior physical characteristics comprising a bituminous binder, from 13% to 25% by weight of exploded wood fiber and a non-fibrous, acid-resistant filler.

8. The article claimed in claim 7, comprising also as an ingredient from 0.5% to 5% of an incompletely polymerized resin, acid polymerizable to an acid-resistant stage, and chosen from a class consisting of partially polymerized furfuryl alcohol, phenol-furfural, phenol-formaldehyde and mixtures thereof.

9. A bituminous molding composition containing a bituminous binder, a finely divided non-fibrous, acid-resistant filler, and exploded wood fiber as a fibrous reinforcement, the said exploded wood fiber being substantially 13% to 25% by weight of the composition, and the said fiber being of such size as to pass a -mesh screen and be retained on a l00-mesh screen in the Clark classifier.

10. A molding composition consisting of substantially 14% exploded wood fiber, 33.6% talc, 48.4% bituminous binder and 3% of an incompletely polymerized resin acid polymerizable to an acid-resistant state, and chosen from a class consisting of partially polymerized furfuryl aleohol, phenol-furfural, phenol-formaldehyde and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,501,995 Dillehay Mar. 28, 1950 2,516,847 Boehm Aug. 1, 1950 2,601,597 Daniel June 24, 1952

Claims (1)

1. AN ACID-RESISTANT MOLDING COMPOSITION COMPRISING AS A FIBROUS REINFORCEMENT SUBSTANTIALLY 13% TO 25% OF EXPLODED WOOD FIBER AND SUNSTANTIALLY 40% TO 13% OF NON-FIBROUS, FINELY DIVIDED, ACID-RESISTANT FILLER, THE BALANCE BEING A BITUMINOUS BINDER.