Patented Apr. 1, 1952 2,591,077

UNITED STATES PATENT OFFICE 2,591,077 METHOD OF PRODUCING ATHERMOPLAS TIC CoMPosITION Bayard T. Lamborn, Matawan, N.J., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Application April 12, 1951, .. Serial No. 220,733 3 Claims. (C. 106-196) This invention relates to a method for pro uniformly distributed throughout the film also ducing thermoplastic composi about 17% diethyl phthalate distributed through tions. In a specific aspect this invention relates the film in greatest concentration near the sur to a method for producing a thermoplastic com face and in gradually diminishing concentration position containing cellulose triacetate in an inwardly from the Surface. The film was swollen amount within the range of 10 to 50%. by the plasticizer and the surface was still slightly Cellulose triacetate scrap such as that used in wet with plasticizer in Small areas. Microscopic photographic film has heretofore been recovered examinations of a cross section showed a gradual by Solution processes for re-use in films, or it has decrease of plasticizer content, as indicated by been dissolved in organic such as acetic 0 degree of Swelling, inwardly from the surface. acid and subjected to hydrolysis conditions for Part of this film was cut into strips 3 mm. by 35 conversion to a secondary acetate which is then mm. by 0.15 mm. for kneading with plasticized directly useful for conversion to plastics. Cellu secondary cellulose acetate. lose triacetate scrap is not thermoplastic in the A plastic composition containing both cellulose commonly accepted sense of the term and has, s triacetate and secondary cellulose acetate was therefore, not been considered to be useful as a compounded by kneading 206 parts cellulose ace plastic in thermoplastic compositions or to be tate flake (53.5% combined ) with 185 compoundable into a thermoplastic cellulose ace parts diethyl phthalate on a heated (about 150 tate molding composition in the usual solventless C.) two-roll mill with differential rolls until a mixing procedures commonly used for secondary 20 completely colloided mix was obtained. Then 285 cellulose acetate compositions. parts of the cut strips of treated scrap film Now in accordance with the present invention, Swollen with the plasticizer was added in incre it has been found that a homogeneous thermo ments of 75 to 100 parts with kneading to a com plastic cellulose acetate molding composition con pletely colloided and uniformly blended mix be taining cellulose triacetate in an amount up to : tween increments. The resulting plastic com about 50% of the total cellulose acetate in the position was sheeted from the rolls and com composition and colloided therewith is produced minuted to a molding powder containing 58.3% by kneading a colloided secondary cellulose ace cellulose acetate and 41.7% plasticizer. Disks tate of thermoplastic properties under heat and and bars were molded in an injection press. The pressure in the absence of volatile solvents while 30 impact strength was 4.3 foot pounds per inch gradually adding thereto plasticized cellulose ace notch, the flow temperature was 163 C. (term tate of high combined acetic acid content in the perature at which plastic flows one inch in two form of particles which have been softened or minutes), and the hardness was 55 (Rockwell Swelled with additional plasticizer so as to have R. Scale). a gradually decreasing plasticizer content from 35 the surface inwardly, and continuing the knead When this experiment was repeated with a film ing until a uniformly and homogeneously col cast from a scrap cellulose triacetate solution loided plastic mass is obtained. The thermo containing added dimethyl phthalate so that the plastic cellulose acetate composition so obtained film contained a total of 34% plasticizer uni is useful for extrusion and iniection molding. 40 formly distributed in the film, the strips of The following examples illustrate the manner plasticized scrap film did not colloid with the sec in which the process of this invention is carried ondary cellulose acetate and appeared to act out and show properties of a typical plastic com only as a filler therefor. position obtained. All parts and percentages un Eacample II less otherwise noted are parts by weight. 45 Example I A portion of the film which had been treated at 100° C. for 1 hour for penetration of the Cellulose triacetate scrap motion picture film plasticizer as in Example I was treated at 100° C. base from which the emulsion layer and subbing . for an additional hour. A cross section of the layer had been removed was run through a bath film showed a more even distribution of the of diethyl phthalate with wiping blades to spread plasticizer in the film and surface scrapings a thin coating of plasticizer on each side. The analyzed 50-60% plasticizer. Slivers cut from film was then rolled and stored at 100° C. for 1. this film and subjected to compounding by knead hour. The resulting film contained besides about ing under heat and pressure in the absence of 17% triphenyl phosphate plasticizer originally volatile as in Example I gave a plastic 2,591,077 3 4. composition substantially identical with that of in radius. However, if the cellulose triacetate Example I. consists of open, spongelike particles so as to Eacample III present a high surface per unit volume, the gross dimensions of the particles may be greater. Films which had been cut into slivers and wet 5 Scrap film up to about 0.20 mm. thickness is with diethyl phthalate in sufficient amount to operable but Scrap film of 0.15 mm. or less is provide 17% plasticizer in addition to the 17% preferable. The film may be used in long strips already distributed in the plasticized scrap film but is preferably cut into small strips or slivers but not allowed to age so as to permit penetra to aid in the mixing process. The term "par tion of the additional plasticizer could not be col O ticles' is intended to include strips of film as well loided and homogeneously blended with the Sec as slivers or chips of film, cellulose triacetate ondary cellulose acetate-plasticizer composition flake, and the like. - of Example I employing hot colloiding methods. While the dimensional characteristics of the The slivers appeared to remain in the mass un particles of cellulose triacetate are of importance changed. The plasticizer on the surface ap 5 for the production of a plasticizer-treated cellu parently was colloided with the secondary cellu lose triacetate conditioned for admixing with sec lose acetate preferentially in the kneading opera ondary cellulose acetate by hot colloiding tion on the hot two-roll mill. methods, the dimensional characteristics are of Following the procedure of either Example I or less importance after the particles are swollen II, up to about 50% by weight cellulose triacetate 20 with plasticizer. Thus the dimensions when based on total cellulose acetate can be incorpo Swollen may be up to twice that of the unswollen rated into a highly satisfactory and useful ther particles. Moreover, the particles may be reduced moplastic molding composition. Heretofore, it in overall size after swelling, if desired. For in has not been considered possible to introduce cel stance, film swollen in coiled strips or sheets may lulose triacetate into a colloided plastic mix suit be cut to Smaller dimension and be suitable for able for molding purposes by a hot colloiding proc conversion into a plastic composition; for each ess in the absence of volatile solvents. The present particle will have substantially the requirement process depends upon the treatment of the cellu of high plasticizer concentration at the surface lose triacetate in such a Way that it is highly with gradually decreasing concentration inwardly plasticized near the surface with gradually de 30 toward a point at the greatest distance from the creasing plasticizer content toward the center. Surface. In this way the process is effected without intro Cellulose triacetate within the scope of this in duction of so large an amount of plasticizer as to vention is considered to be any cellulose triacetate destroy the useful properties of the plastic mass. having 59 to 62.5% combined acetate acid, and The cellulose triacetate must contain at least 15% wherever the term 'cellulose triacetate' is used, plasticizer as the greatest distance from the sur cellulose acetate of such a range of combined face so that the last portion will colloid and blend acetic acid content is meant. Scrap film cellus uniformly and completely in the mass. Thus, if lose triacetate generally has a combined acetic unplasticized cellulose triacetate is plasticized acid content in the range of 60 to 62%. only with the plasticizer added and without treat 40 Secondary cellulose acetate used in the process ment other than aging to bring about diffusion, of this invention is cellulose acetate of 52 to 57% the plasticizer would have to diffuse sufficiently combined acetic acid and is the type known to to bring the plasticizer content to a minimum of be useful in thermoplastic compositions. Sec 15% at the greatest distance from the surface. ondary cellulose acetate of 53 to 56% combined In such a treated cellulose triacetate no portion acetic acid content is preferred. Either new or would contain less than 15% plasticizer and the scrap secondary cellulose acetate may be used. Surface would contain Substantially more, at least The plasticizers useful in the process of this about 45%, and preferably about 50% to 60% invention include triacetin, triethyl phosphate, plasticizer. Since scrap film already contains dimethyl phthalate, and diethyl phthalate for 15-20% plasticizer, scrap film is a preferable use as the additional plasticizer for diffusion into Source of cellulose triacetate. In such scrap film the cellulose triacetate particles. The cellulose the diffusion of added plasticizer is more readily triacetate to be treated with any of these addi brought about and the minimum plasticizer con tional plasticizers may already contain any of tent is already present throughout the cellulose the above plasticizers or any plasticizer useful triacetate. The added plasticizer is necessary in 55 with cellulose triacetate films uniformly colloided either case and it must be present in concentra therewith. The plasticizer for the secondary tions of at least about 45% and preferably 50% cellulose acetate colloided mass to which the cel to 60% at the surface with gradual decrease in lulose triacetate is added must also be either a concentration inwardly from the surface of the plasticizer for cellulose triacetate films or be one film, The total plasticizer should not be less than of the additional plasticizers listed above. The about 35% of the weight of the plasticizer-treated additional plasticizers are classified as liquid plas particle. - ticizers completely compatible perse with cellu The process of this invention is also applicable lose triacetate in all proportions. At least 90% to cellulose triacetate in forms other than films, : Such as virgin cellulose triacetate flake, for ex of the additional plasticizer should be completely ample; but due to the requirement of gradual de 65 compatible in all proportions with cellulose tri Crease in concentration of the plasticizer in acetate and should contain no other components Wardly from the Surface, the size or shape of the which detract from its compatibility when pres cellulose triacetate particles is of some impor ent in amounts up to about 10%. Besides the tance. For practical operation, it has been deter plasticizers set forth above, a "plasticizing acti mined that no point in the cellulose triacetate 70 vator' in amount up to 10% of the plasticizer particles should be more than about 0.10 mm. may be used in admixture with the plasticizer from a surface through which the added plasti used for treatment of the cellulose triacetate. cizer is to diffuse. Thus, if the particles are of a The use of Such a plasticizing activator aids in shape that presents a minimum surface per unit the penetration or diffusion of the plasticizer volume, they must be smaller than about 0.10 mm. 75 into the cellulose triacetate. The materials which 2,591,077 have been found to function as plasticizing acti and for general molding purposes where second vators are: the liquid water-soluble glycols and ary cellulose acetate compositions are useful. polymers thereof containing only carbon, hydro The advantage of the process is that it makes gen, and oxygen and boiling within the range of use of scrap film which has heretofore required about 195° to 300° C. This includes ethylene 5 solvents for direct utilization and has generally glycol, propylene glycol, and polymers thereof involved removal of the plasticizer and subsequent such as di- and tri-ethylene glycols and di- and hydrolysis to a usable secondary cellulose acetate. tri-propylene glycols, and the like. These glycols What I claim and desire to protect by Letters improve the plasticizing action and do not detract Patent is: from the cellulose acetate plasticizers when pres 0 1. The method of producing a thermoplastic ent therein in amounts up to about 10% of the cellulose acetate composition containing cellulose total plasticizer. triacetate in an amount within the range of about The aging of the cellulose triacetate with plas 10 to 50% which comprises kneading secondary ticizer is generally accomplished at elevated tem cellulose acetate plasticized with about 20% to perature to shorten the time required. Tempera about 30% plasticizer therefor at an elevated tures of 60-100° C. are suitable, but temperatures temperature below the temperature of decom up to about 200° C. may be used, if desired. position thereof while gradually adding thereto Kneading may be accomplished on a two-roll particles of cellulose triacetate, said particles be mill, a Banbury mixer, a plastic extruder, or sim ing permeated with plasticizer in concentration ilar hot colloiding and kneading apparatus. varying from at least about 45% at the surface The kneading temperature must be sufficient thereof to about 15 to 20% at the greatest dis to make kneading possible. The minimum tem tance from the surface, and continuing kneading perature is generally about 150° C. The maxi until a uniformly colloided plastic mass is ob mum temperature will be that below which de tained. composition takes place and Will in general be 2 5 below about 300° C. 2. The method of producing a thermoplastic The amount of plasticizer used in the process cellulose acetate composition containing cellulose of this invention will be governed by the char triacetate in an amount within the range of acteristics of the materials used and the proper about 10 to 50% which comprises kneading sec ties desired. Secondary cellulose acetate will re- : ondary cellulose acetate plasticized with about quire at least about 20% plasticizer and prefer 20% to about 30% plasticizer therefor at an ele ably 25 to 30% pasticizer for satisfactory knead wated temperature below the temperature of de ing as the Cellulose triacetate is added and col composition thereof while gradually adding loided therewith. Since more plasticizer will be thereto particles of cellulose triacetate, said par required with the cellulose triacetate, it is prefer ticles being colloided with at least 15% plasti able to keep the amount used with the secondary 3 5 cizer and softened with additional plasticizer cellulose acetate low when a low average is de distributed in gradually decreasing concentration sired in the finished plastic. The cellulose tri inwardly from at least about 45% at the surface acetate should have an average plasticizer con thereof to about 15 to 20% at the greatest dis tent Or, as better expressed, total plasticizer con tance from a surface, and continuing kneading tent of about 35% plasticizer as a minimum. 40 until a uniformly colloided plastic mass is ob This, as pointed out above, is to be distributed tained. from the surface inwardly over a range of con 3. The method of producing a thermoplastic centration from at least about 45% at the sur cellulose acetate composition containing cellulose face to at least 15% at the point farthest from triacetate in an amount within the range of about the Surface and may be as high as 100% at the 10 to 50% which comprises kneading secondary surface. The maximum at the center will depend cellulose acetate plasticized with about 20% to upon the total that can be allowed for the final about 30% plasticizer therefor at an elevated composition for the properties desired therein, temperature below the temperature of decom since operability is not destroyed by a large position thereof while gradually adding theret) amount of plasticizer. However, the properties particles of cellulose triacetate, said particles be of the finished product will be greatly affected ing colloided with at least 15% plasticizer and thereby and too high a plasticizer content may softened with additional plasticizer distributed in limit greatly the utility of the completed product. gradually decreasing concentration inwardly In general, the final product should contain as from about 50 to 60% at the surface thereof to much below 50% total plasticizer as possible and 5 5 about 15 to 20% at the greatest distance from the actual amount that can be used will depend a surface, and continuing kneading until a uni upon the amount of cellulose triacetate incor formly colloided plastic mass is obtained. porated and the minimum amount of plasticizer that can be used therewith. Up to about 50% BAYARD T. LAMBORN, cellulose triacetate based on total cellulose ace 30 tate in the composition can be tolerated in a REFERENCEs CITED finished plastic composition containing cellulose The following references are of record in the triacetate and secondary cellulose acetate. The file of this patent: minimum plasticizer content of such a composi tion produced by this process would thus have UNITED STATEs PATENTs slightly less than about 30% plasticizer. The Number Name Date desired range would be about 35%. Higher plas 1910,948 Dreyfus ------May 23, 1933 ticizer contents are much more easily obtained simply by kneading in more plasticizer into the 1953,956 Dreyfus ------Apr. 10, 1934 composition during the compounding process if 1999,405 Dreyfus ------Apr. 30, 1935 more plasticizer is desired. FOREIGN PATENTS The plastic compositions of this invention are Number Country Date useful for coating fabrics and other materials 417.937 Great Britain ------Oct. 11, 1934