UNITED STATES PATENT OFFICE 2,591,077 METHOD of PRODUCING ATHERMOPLAS TIC CELLULOSE ACETATE Composition Bayard T

Patented Apr. 1, 1952 2,591,077 UNITED STATES PATENT OFFICE 2,591,077 METHOD OF PRODUCING ATHERMOPLAS TIC CELLULOSE ACETATE 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 cellulose acetate 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 solvents 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 acetic acid) 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 solvent 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.

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