FIELD OF THE INVENTION
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The present invention relates to cellulose esters, and specifically, to cellulose esters that exhibit improved degradation.
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OF THE INVENTION
Typical cigarette filters are made from a continuous-filament tow band of cellulose acetate-based fibers, called cellulose acetate tow, or simply acetate tow. The use of acetate tow to make filters is described in various patents, and the tow may be plasticized. See, for example, U.S. Pat. No. 2,794,239.
Instead of continuous fibers, staple fibers may be used which are shorter, and which may assist in the ultimate degradation of the filters. See, for example, U.S. Pat. No. 3,658,626 which discloses the production of staple fiber smoke filter elements and the like directly from a continuous filamentary tow. These staple fibers also may be plasticized.
Acetate tow for cigarette fibers is typically made up of Y-shaped, small-filament-denier fibers which are intentionally highly crimped and entangled, as described in U.S. Pat. No. 2,953,838. The Y-shape allows optimum cigarette filters with the lowest weight for a given pressure drop compared to other fiber shapes. See U.S. Pat. No. 2,829,027. The small-filament-denier fibers, typically in the range of 1.6-8 denier per filament (dpf), are used to make efficient filters. In constructing a filter, the crimp of the fibers allows improved filter firmness and reduced tow weight for a given pressure drop.
The conversion of acetate tow into cigarette filters may be accomplished by means of a tow conditioning system and a plugmaker, as described, for example, in U.S. Pat. No. 3,017,309. The tow conditioning system withdraws the tow from the bale, spreads and de-registers (“blooms”) the fibers, and delivers the tow to the plugmaker. The plugmaker compresses the tow, wraps it with plugwrap paper, and cuts it into rods of suitable length. To further increase filter firmness, a nonvolatile solvent may be added to solvent-bond the fibers together. These solvent-bonding agents are called plasticizers in the trade, and historically have included triacetin (glycerol triacetate), diethylene glycol diacetate, triethylene glycol diacetate, tripropionin, acetyl triethyl citrate, and triethyl citrate. Waxes have also been used to increase filter firmness. See, for example, U.S. Pat. No. 2,904,050.
Conventional plasticizer fiber-to-fiber bonding agents work well for bonding and selective filtration. However, plasticizers typically are not water-soluble, and the fibers will remain bonded over extended periods of time. In fact, conventional cigarette filters can require years to degrade and disintegrate when discarded, due to the highly entangled nature of the filter fibers, the solvent bonding between the fibers, and the inherent slow degradability of the cellulose acetate polymer. Attempts have therefore been made to develop cigarette filters having improved degradability.
U.S. Pat. No. 5,947,126 discloses a bundle of cellulose acetate fibers bonded with a water-soluble fiber-to-fiber bonding agent. The bonded fibers are wrapped in a paper having opposing ends secured together with a water-soluble plug wrap adhesive, and a plurality of cuts are made to extend more than one half way through the bundle wrapped fibers. A tobacco smoke filter is thus provided that disintegrates and degrades in a relatively short period of time.
U.S. Pat. No. 5,947,127 discloses a filter rod produced by adding a water-soluble polymer in the form of an aqueous solution or dispersion, or in a particulate form, to a tow of cellulose ester fiber. The tobacco filter is said to be highly wet-disintegratable and, hence, contributes to mitigation of environmental pollution. The environmental degradability of the fiber can be increased by incorporating a biodegradation accelerator such as citric acid, tartaric acid, malic acid, etc. and/or a photodegradation accelerator such as anatase-form titanium dioxide, or titanium dioxide, preferably anatase-form titanium dioxide, may be provided as a whitening agent.
Research Disclosure, June 1996, pp. 375-77 discloses that the use of plasticizers used to form filters from acetate tow decrease the degradation of cigarette filters by holding the fibers together, but that simply leaving off the plasticizer will not allow the rapid disintegration of the filters in the environment due to fiber entanglement. The authors therefore propose environmentally disintegratable filters made using uncommon types of tow, that is, fibers which have properties that will significantly reduce entanglement when wet.
U.S. Pat. No. 7,435,208 discloses cigarette filters that comprise an elongate filter component having a longitudinal axis. A plurality of spaced-apart slits, generally perpendicular to the longitudinal axis of the filter component, partially extend into the component. The slits enable the filter to disintegrate and more readily degrade after being used and discarded.
U.S. Pat. Nos. 5,491,024 and 5,647,383 disclose a man-made fiber comprising a cellulose ester and 0.05 to 5.0% by weight of a titanium dioxide having an average particle size of less than 100 nanometers. The titanium dioxide is added to the “dope” (i.e., the solvated cellulose ester) prior to extrusion into the tow. Addition of the titanium dioxide may be at any convenient point prior to extrusion. The titanium dioxide is preferably an uncoated anatase material having an average particle size less than 10 nanometers and a specific surface area of about 250 m2/g.
U.S. Pat. No. 5,512,230 discloses a method for spinning a cellulose acetate fiber having a low degree of substitution per anhydroglucose unit (DS/AGU) of the cellulose acetate. The addition of 5 to 40 weight percent water to cellulose acetate (CA)/acetone spinning solutions (dopes) is said to produce dopes that will allow fibers to be solvent spun using CA with a DS/AGU from 1.9 to 2.2.
U.S. Pat. No. 5,970,988 discloses cellulose ester fibers having an intermediate degree of substitution per anhydroglucose unit (DS/AGU) that contain pigments which act as photooxidation catalysts. The fibers are useful as filter materials for tobacco products. The filter materials thus provided are easily dispersible and biodegradable and do not persist in the environment. The pigment may be titanium dioxide and is provided within the fiber, but in amounts greater than are typical for use as a whitening agent.
U.S. Patent Publication. No. 2009/0151738 discloses a degradable cigarette filter that includes a filter element of a bloomed cellulose acetate tow, a plug wrap surrounding the filter element, and either a coating or a pill in contact with the tow. The coating and/or pill may be composed of a material adapted to catalyze hydrolysis of the cellulose acetate tow and a water-soluble matrix material such that when water contacts the water-soluble matrix material, the material adapted to catalyze hydrolysis is released and catalyzes the hydrolysis, and subsequent degradation, of the cellulose acetate tow.
WO 2010/017989 discloses a photodegradable plastic comprising cellulose esters and also, if appropriate, additives. The photodegradable plastic comprises a dispersed photocatalytic carbon-modified titanium dioxide. The photodegradable plastic is said to exhibit a surprisingly high increase in photocatalytic degradability when compared with products in which a conventional or other modified titanium dioxide is used. The photodegradable plastic can, for example, first be further processed to give a filter tow.
WO 2009/093051 and U.S. Patent Publication. No. 2011/0023900 disclose a tobacco smoke filter or filter element comprising a cylindrical plug of a substantially homogeneous filtering material of circumference between 14.0 and 23.2 mm, wherein the substantially homogeneous filtering material comprises a plurality of randomly oriented staple fibers.
The photocatalytic activity of mixed-phase titanium dioxide has been investigated. See “Explaining the enhanced photocatalytic activity of Degussa P25 mixed-phase TiO2 using EPR”, J. Phys. Chem. B 107 (2003) 4545-4549. See also “Probing reaction mechanisms in mixed phase TiO2 by EPR”, Journal of Electron Spectroscopy and Related Phenomena, 150 (2006) 155-163.
Titanium Dioxide P25, Manufacture—Properties—Applications, Technical Bulletin Fine Particles, Number 80, Degussa Aerosil & Silanes Product Literature (Undated) discusses commercial uses of mixed-phase titanium dioxide, including use as a photocatalyst and as a photo-semiconductor.
U.S. Pat. No. 5,720,803 discloses a composition comprising a cellulose ester including at least 10 weight % of a low-substituted cellulose ester having an average degree of substitution not exceeding 2.15 and giving a 4-week decomposition rate of at least 60 weight % as determined using the amount of evolution of carbon dioxide as an indicator in accordance with ASTM 125209-91. The composition may contain a plasticizer, an aliphatic polyester, a photolysis accelerator such as anatase type titanium dioxide or a biodegradation accelerator such as organic acids and their esters. The low-substituted cellulose ester may be a cellulose ester having an average degree of polymerization from 50 to 250, an average degree of substitution from 1.0 to 2.15 and a residual alkali metal/alkaline earth metal-to-residual sulfuric acid equivalent ratio of 0.1 to 1.1. The biodegradable cellulose ester composition is said to be suitable for the manufacture of various articles including fibrous articles such as tobacco filters.
U.S. Pat. No. 5,478,386 discloses a composition that includes a cellulose ester including at least 10 weight % of a low-substituted cellulose ester having an average degree of substitution not exceeding 2.15. The composition may contain a plasticizer, an aliphatic polyester, a photolysis accelerator such as anatase-type titanium dioxide, or a biodegradation accelerator such as organic acids and their esters.
U.S. Pat. No. 5,242,880 discloses novel titania comprising anatase titanium dioxide and sodium, potassium, calcium, magnesium, barium, zinc, or magnesium salts of sulfuric or phosphoric acid. The titania are said to be useful in the pigmentation of oxidizable polymers, while at the same time providing a catalyst system for the photooxidation of the oxidizable polymers.
U.S. Pat. No. 5,804,296 discloses a composition comprising a cellulose acetate or other cellulose ester, and an anatase-type titanium oxide having a specific surface area of not less than 30 m2/g, a primary particle size of 0.001 to 0.07 μm, or a specific surface area of not less than 30 m2/g and a primary particle size of 0.001 to 0.07 μm. For improving the photodegradability and the dispersibility, the surface of the titanium oxide may be treated with a phosphoric acid salt or other phosphorus compound, a polyhydric alcohol, an amino acid or others. The composition may further contain a plasticizer and/or an aliphatic polyester, a biodegradation accelerator (e.g. organic acids or esters thereof).
WO 1995/29209 discloses pigmented cellulose acetate filaments produced by mixing a dispersion of titanium dioxide in a carboxylate ester of a polyhydric alcohol with cellulose acetate and a solvent for cellulose acetate. The resulting dispersion is dry spun to produce pigmented cellulose acetate filaments.
Balázs, Nándor et al.; “The effect of particle shape on the activity of nanocrystalline TiO2 photocatalysts in phenol decomposition”; Applied Catalysis B: Environmental, 84 (2008), pp. 356-362, investigated the effect of the morphology, that is spherical versus polyhedral, on the photocatalytic activity of nanocrystalline titanium dioxide photocatalysts.
Byrne, H. E. et al.; “Characterization of HF-catalyzed silica gels doped with Degussa P25 titanium dioxide”; Journal of Non-Crystalline Solids, 355 (2009), pp. 525-530, synthesized SiO2/TiO2 composites by adding Degussa P25 TiO2 to a liquid sol that was catalyzed by HNO3 and HF acids. The composites were then characterized by several different analytical techniques.
Hurum, D. C. et al., in “Probing reaction mechanisms in mixed phase TiO2 by EPR”; Journal of Electron Spectroscopy and Related Phenomena, 150 (2006), pp. 155-163, investigated charge separation processes in mixed phase TiO2 photocatalysts by electron paramagnetic resonance spectroscopy.
Janus, M. et al., in “Carbon-modified TiO2 photocatalyst by ethanol carbonisation”; Applied Catalysis B: Environmental; 63 (2006), pp. 272-276, investigated the effect on photocatalytic activity of modifying titanium dioxide powder by carbon via ethanol carbonization.
Janus, M. et al., in “Carbon Modified TiO2 Photocatalyst with Enhanced Adsorptivity for Dyes from Water”; Catal. Lett.; 131 (2009), pp. 506-511, obtained a new photocatalyst by modifying a commercial anatase titanium dioxide in a pressure reactor in an ethanol atmosphere. The photocatalytic activity of the material was tested during three azo dyes decompositions.
Lu, Xujie et al., in “Intelligent Hydrated-Sulfate Template Assisted Preparation of Nanoporous TiO2 Spheres and Their Visible-Light Application”; ACS Applied Materials & Interfaces; December 2010, investigated nanoporous titanium dioxide spheres and their applications, including their photocatalytic activities.
Juergen Puls et al., in “Degradation of Cellulose Acetate-Based Materials: A Review”; Journal of Polymers and the Environment: Volume 19, Issue 1; 2011; pp. 152-165, reviewed studies conducted on the biogradability of cellulose acetate, including photo-degradation.
There remains a need, however, for degradable cellulose esters such as those used to make cigarette filters, especially those that exhibit an increased ability to degrade in the environment using materials that may be applied to the filters in a variety of manners.
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OF THE INVENTION
In one aspect, the invention relates to articles comprising a cellulose ester having incorporated therein or thereon mixed-phase titanium dioxide particles. The article may be in the form of a molded article, or in the form of cellulose ester fibers, for example in the form of a yarn or a fabric.
Alternatively, the cellulose ester fibers may be in the form of a filter prepared by a process that includes the steps of applying a plasticizer, having the mixed-phase titanium dioxide particles dispersed therein, to the cellulose ester fibers to obtain plasticized cellulose ester fibers; and thereafter forming the plasticized cellulose ester fibers into a filter. In this aspect, the plasticizer may include one or more of: triacetin (glycerol triacetate), diethylene glycol diacetate, triethylene glycol diacetate, methyl phthalyl ethyl glycollate, dibutyl phthalate, tripropionin, acetyl triethyl citrate, triethyl citrate, and mixtures of triacetin and one or more polyethylene glycols. When the articles of the invention are in the form of filters, the filters may be provided with one or more slits, and may be useful, for example, for use in cigarettes.
The mixed-phase titanium dioxide particles useful according to the invention may comprise, for example, an anatase phase present in an amount from 50% to 98%, and a rutile phase present in an amount from 2% to 50%, in each case as measured by x-ray crystallography. The particles may have a surface area, for example, from about 10 to about 300 sq. m/g, and may independently have an average particle size from about 1 nm to about 100 nm, or from 5 nm to 50 nm.
The amount of mixed-phase titanium dioxide particles provided to the articles according to the invention may vary widely, for example from about 0.01 to about 20 wt. %, based on the weight of the article.