GB2171334A - Cellulose acetate moulding containing an odoriferous substance - Google Patents

Abstract

A porous moulding of cellulose acetate is provided which comprises cellulose acetate having a combined acetic acid content of 50 to 58%, a pore volume of at least 0.65 cc/g and a collapsing strength of at least 10 kg and an odoriferous substance contained in the pores of cellulose acetate.

Description

SPECIFICATION Cellulose acetate moulding containing an odoriferous substance The present invention relates to a porous moulding containing an odoriferous substance which may, for example, be obtained by impregnating a cellulose acetate-based porous moulding with at least one odoriferous substance such as, for example, an aromatizing agent or a volatile insect repellent by adsorption.

It is known that, for example, scent bags and pastilles containing means for stably and slo.vly releasing an odoriferous substance, such as a perfume or a volatile insect repellent over a long period of time were devised a long time ago.

In recent years, proposals have been made for obtaining a plastic article having aromaticity by allowing an adsorptive porous powder to adsorb an odoriferous substance, dispersing the powder in a gaspermeable plastic and moulding the plastic after pelletization (Japanese Patent Publication h,o.s283/ 1968); and for incorporating a volatile chemical in a thermoplastic elastomer comprising blocks containing polymer segments having a strong intermolecular bonding force and those having a weak intermolecular bonding force (Japanese Patent Laid-Open No.115377/1981).

Scent bags, pastilles and the products obtained by the above processes, however, have drawbacks in that their perfume contents are as low as no more than about ten per cent that the persistence of their fragrance is short and that the fragrance is weak.

When imparting aromaticity to a plastic article, restrictions are placed on, for example, the amount and kind of the aromatizing agent (perfume) added to the plastic, because it does not usually have sufficient compatibility with plastics, and is easily evaporated during moulding after pelletization. In addition, it is difficult to use an easily volatile aromatizing agent.

When the thermoplastic elastomer having blocks comprising polymer segments having a strong inter molecular bonding force and those having a weak intermolecular bonding force is used as a carrier for adsorption and volatilization of a volatile chemical, there is a restriction that the choice must be made from those chemicals and diluents therefor which show affinity for the polymer segments having a weak intermolecular bonding force but show less affinity for the polymer segments having a strong intermo lecular bonding force.

The requirements for a material (carrier) for adsorbing an odoriferous substance and releasing the adsorbed odoriferous substance are as follows. Firstly, the odoriferous substance is chemically inert to the carrier. Secondly, the carrier can fully adsorb the odoriferous substance. Thirdly, the external shape of the carrier does not change substantially after adsorption of the odoriferous substance. Fourthly, the odoriferous substance is released at a moderate rate and the composition of the released component does not change appreciably with the lapse of time. The third requirement that the external shape of a carrier does not change substantially is particularly important for designing commercial products when the carrier comprises a moulding.

We have found that a porous moulding based on cellulose acetate of a high pore volume fully adsorbs an odoriferous substance without substantially undergoing changes of its external shape and of continuously and consistently releasing the adsorbed odoriferous substance over a long period of time.

According to the present invention a porous moulding of cellulose acetate is provided which comprises cellulose acetate having a combined acetic acid content of 50 to 58%, a pore volume of at least 0.65 cc/g and a collapsing strength of at least 10 kg and an odoriferous substance contained in the pores of cellulose acetate.

The expression "combined acetic acid content" has the same meaning as "degree of acetylation".

The cellulose acetate used in the present invention is one containing hydroxyl and acetate groups and having a combined acetic acid content of 50 to 58%. The porous moulding can be formed from a solution of cellulose acetate in acetone or acetic acid, coagulating it by extrusion into a suitable coagulation bath, for example, an aqueous acetone solution or an aqueous acetic acid solution, moulding the e,qrudate while it still exhibits plasticity, and washing the product. The porous moulding can take a variety of forms, among which spherical particles are advantageous from the viewpoint of, for example, fluidity, strength or surface area, and those particles which have a diameter of 0.5 to 10 mm and a sphericity of at least 0.8 are particularly advantageous.In addition, it is possible to use a moulding of any desired shape, prepared by forming the above moulding. The porous moulding produced by this process shows a large collapsing strength in spite of its large pore volume. The fact that the cellulose acetate according to the present invention has a combined acetic acid content falling within the above range is thought to contribute to the features that the moulding can adsorb a wide variety of aromatizing agents by virtue of a good balance between the hydroxyl groups and the acetate groups, that when the moulding releases the adsorbed aromatizing agent, the composition of the released component does not change with the lapse of time even when a compounded aromatizing agent is used, and that the persistance of fragrance is good.A pore volume of below 0.65 cc/g is not practical because the amount of an odoriferous substance which can be adsorbed is low. A collapsing strength of below 10 kg is not practical because, for example, the particles undergo disintegration. When spherical particles have a particle diameter of below 0.5 mm or above 10 mm, then, for example, a problem of washing arises during their production, or they are difficult to handle in adsorbing an odoriferous substance and such particles are therefore not pre ferred.

It is also possible to use a product obtained by saponifying the outer surface of the porous moulding of the present invention.

Cellulose acetate essentially shows considerable affinity for polar substances such as esters, atones, lactones, aldehydes or phenols, so that, for example, some kinds of perfumes supported on the moulding cause surface stickiness of the moulding, and the surface of the moulding becomes sticky or the particles of the moulding stick together. These phenomena can be overcome by saponifying the outer sun'ace of the porous moulding. The saponification can be performed for example by immersing the porous cellulose acetate moulding in an aqueous solution of an alkali, preferably sodium hydroxide, for a certain time.Although the degree of regeneration of the cellulose acetate into cellulose in this case depends, for example, on the concentration of the aqueous solution of alkali and the soaking time, porous mouldings of a high cellulose content, which are undesirable for use in a solid aromatizing agent aimed in the present invention, are produced when the above treatment is carried out with a high-concentration solution of alkali or for a long time. Therefore, the concentration of the aqueous sodium hydroxide solution must be 0.2 to 5%, preferably 0.5 to 2%, and the soaking time is 1 to 10 minutes, preferably 2 to 5 minutes.

The immersing temperature is preferably 10 to 50"C, more preferably a temperature around ordinary room temperature. In order to decrease the amount of the alkali remaining after the saponification, it is necessary to wash the saponificate thoroughly, for remaining alkali directly causes the degradation of a perfume and this, in turn, causes an unbalanced aroma of a compounded perfume as well as degradation of the aroma.

When a porous cellulose acetate moulding is saponified by the above method, the saponification occurs on only the surface of the moulding. This fact can be affirmed by the fact that the surface appearance is improved and the average combined acetic acid content can be kept at a value which corresponds to at least 90% of that before the treatment.

Examples of the odoriferous substances which can be used in the present invention are single perfumes, compounded perfumes, volatile insect repellents, volatile antibacterial agents, and volatile mould inhibitors. It is also possible to use these volatile substances after dilution with diluents.

The impregnation of a porous moulding with an odoriferous substance can be performed, for example, by immersing the porous moulding in the odoriferous substance or spraying it with the odoriferous sub- stance. It is preferable from an economical viewpoint that the content of an odoriferous substance in the aromatizing agent of the present invention is 50 to 60% by weight. Further, it is apparent from the gist of the present invention that the cellulose acetate according to the present invention may be, for example, cellulose acetate butyrate, or cellulose acetate propionate.

It is also possible for the cellulose acetate used in the present invention to contain, for example, plasticizers, dyes, pigments, antistatic agents or antioxidants, if necessary or desired.

Impregnation limits of perfume were measured on conventional products and the product of the present invention to examine their characteristics. Table 1 shows the results.

Although the composition of each product tested varies slightly and the result depends on the quality of a perfume, it can be concluded on the whole that the product of the present invention is excellent in that it has a large impregnation iimit of perfume and a hard structure and shows no surface stickiness due to the perfumes and a good resistance to heat and that the conventional products have drawbacks in respect of shape after impregnation of a perfume, that is EVA is weak to heat and softened when the temperature is increased, the calcium silicate is easily disintegrated, and the silica gel is easily broken.

TABLE 1 Kind of products Impregnation limit* cellulose acetate particles 160 g saponified cellulose acetate particles 120 g calcium silicate pellets 150 g EVA pellets (VA content of 28%) 30 g silica gel spheres 40 g *Note: per 100 g of a base in the accompanying drawings, Figures 1 to 4 are graphs showing the changes in the amounts of odoriferous substances with the lapse of time, measured in the Examples and Comparative Examples.

The present invention will now be described in detail with reference to Examples. In these Examples, combined acetic acid content, sphericity, pore volume, and collapsing strength were measured according to the following methods.

Combined acetic acid content: About 5 g of a powdered sample were dried in a dryer at 100 to 1050C for 2 hours and weighed accurately. 50 cc of purified acetone was added to this sample and the mixture was dissolved completely. 50 cc of a 0.2N aqueous NaOH solution and 50 cc of a 0.2N aqueous HCI solution were added thereto in sequence. The resulting solution was titrated with a 0.2N aqueous NaOH solution using phenolphthalein as an indicator.The degree of acetylation was calculated according to the following equation: Combined acetic acid = (A - B x F x 1.201 x 100 (%) weight (g) of sample wherein A: volume (cc) of 0.2N aqueous NaOH solution added B: volume (cc) of 0.2N aqueous NaOH solution added in a blank test F: factor of 0.2N aqueous NaOH solution Sphericity: 20 particles were taken up at random and the largest and smallest diameters of each particle were measured with a micrometer. The sphericity was determined according to the following equation: sphericity = (smaIlest diameterilargest diameter) 20 Pore volume: A mercury porosimeter (a product of Carlo Erba) was used.The volume of mercury intruded into the pores at a pressure in the range of 0 to 1,000 kg/cm2G corresponded to a volume of pores in the range of 75 to 75,000 . The pore volume is represented by a volume (cc) per gram of the sample.

Collapsing strength: A Monsanto tablet hardness tester (a product of Oiwa Medical Machine Manufacturing Co.Ltd.) was used. An average of the measured values of 10 particles was calculated.

Example 1 Spherical cellulose acetate particles having a combined acetic acid content of 54%, an average particle diameter of 4.0 mm, a sphericity of 0.9, a pore volume of 0.82 cc/g and a collapsing strength of 17 kg were immersed in a compounded Citrus perfume. The amound of the compounded perfume adsorbed after 24 hours was 164% based on the weight of the spherical porous cellulose acetate moulding. The diameter of the spherical porous cellulose acetate moulding did not change appreciably after adsorption.

Figure 1 shows the change in the weight of the spherical porous cellulose acetate moulding containing the adsorbed perfume, obtained when it was left standing in a completely open air at the room temperature, preferably 25 to 29"C.

The moulding continued to relase the aroma of the compounded Citrus perfume over a period of at least one month, and the aroma just after the initiation of the release did not differ appreciably from that after one month.

Example 2 Spherical cellulose acetate particles having a combined acetic acid content of 52%, an average particle diameter of 3.5 mm, a sphericity of 0.87, a pore volume of 0.75 cc/g. and a collapsing strength of 20 kg were immersed in the same compounded perfume as that used in Example 1 to effect adsorption under the same conditions as in Example 1. The amount of the perfume adsorbed was 57%. Figure 1 shows the change in the weight of the spherical porous cellulose acetate moulding containing the adsorbed perfume, obtained when it was left standing in the same way as in Example 1. The release characteristics were substantially the same as those in Example 1.

Example 3 A cubic moulding (pore volume of 0.80 cc/g) having a side of 35 mm formed by using the same spherical porous cellulose acetate moulding as that used in Example 1 was immersed in the same odoriferous substance as that used in Example 1. The amount of the odoriferous substance adsorbed after 24 hours was 160%, based on the weight of the moulding. The moulding did not change appreciably in shape after the adsorption, and persistently released an aroma over a period of at least one month.

Example 4 The same spherical porous cellulose acetate moulding as that used in Example 1 was immersed in a compounded rose perfume for 24 hours. The amount of the odoriferous substance adsorbed was 158%.

The moulding did not change appreciably in its shape after adsorption. This moulding persistently released the aroms of the compounded rose perfume over a period of at least one month. In addition, the aroma just after the initiation of the release was substantially the same as that after about one month.

Comparative example 1 A No.5 filter paper (a product of Toyo Filter Paper Co.,Ltd.) was cut into squares of a size of 2 cm x 2 cm, and these squares were immersed in the same compounded Citrus perfume as that used in Example 1 for 24 hours. The amount of the perfume adsorbed was 93% based on the weight of the filter paper squares. Three of these squares were laid upon each other and left standing in a completely open air at 25 to 29"C. Figure 1 shows the change in the weight with the lapse of time in this case. The aroma was extremely weakened after about 10 days, and it could hardly be detected after about 15 days.

Comparative example 2 When substantially spherical particles (an average particle diameter of 3.5 mm) of an ethylene/vinyl acetate copolymer (vinyl acetate content of 8 mol %) were immersed in the same compounded Citrus perfume as that used in Example 1, the particles were swollen with the lapse of time to such an extent that the diameter increased 2.5-fold.

Example 5 About 100 g of spherical cellulose acetate particles having a combined acetic acid content of 54.5%, an average particle diameter of 3.6 mm, a sphericity of 0.87, a pore volume of 0.82 cc/g, and a collapsing strength of 20 kg were immersed in 500 cc of a 1% aqueous sodium hydroxide solution with stirring at room temperature for 3 minutes. The particles were dewatered in a centrifuge, washed with warm water (40"C) for 3 hours and dried for 3 hours in a dryer at 100 to 110 C to obtain spherical surface-saponified cellulose acetate particles. These particles had a combined acetic acid content of 53.4%, an average particle diameter of 3.2 mm, a sphericity of 0.82, a pore volume of 0.75 cc/g, and a collapsing strength of 15 kg.When these particles were impregnated with 20%, based on the weight of the particles, of Lemon-pH- 5526 (a product of Takasago Corporation), which is based on a terpene hydrocarbon perfume, the impregnation was complete after about 10 minutes. These particles impregnated with perfume did not show surface stickiness nor adhesion among the particles when left standing in a high-temperature chamber of 80"C, thus functioning as a solid aromatizing agent. 10 g of this agent were placed and left standing in a glass Petri dish 10 cm in diameter and 1.5 cm in depth to measure the rate of volatilization at room temperature. Nine days were necessary for 50% volatilization and 45 days were necessary for 90% volatilization. This suggested an excellent effect of slow release.Figure 2 shows the change in the amount of the perfume volatilized with the lapse of time.

Comparative examples 3 and 4 When spherical calcium silicate particles having a particle diameter of 5.0 mm, a sphericity of 0.9 and a collapsing strength of 3.5 kg (Florite R-5), a product of Tokuyama Soda Co., Ltd.) (Comparative Example 3); and EVA pellets (vinyl acetate contents of 28%, particle diameter of 3 to 4 mm) (Comparative Example 4) were impregnated with 20% of the same perfume as that used in Example 5 in the same way as in Example 5, the impregnation was complete after about 5 minutes.

The perfume within these particles was released at a rate such that 50% of the perfume initially present was released after 5 to 8 days, and all of the perfume was released after one month. These particles were fragile and easily disintegrated into powder. Figure 2 shows the change in the amount of the perfume volatilized with the lapse of time.

Example 6 100 g of spherical cellulose acetate particles having a combined acetic acid content of 55.2%, an average particle diameter of 5.3 mm, a sphericity of 0.9, a pore volume of 0.85 cc/g and a collapsing strength of 18 kg were immersed in 500 cc of a 0.5% aqueous sodium hydroxide solution with stirring at room temperature for 5 minutes and treated in the same way as in Example 5 to obtain cellulose acetate particles. The particles had a combined acetic acid content of 54.5%, an average particle diameter of 5.1 mm, a sphericity of 0.85, a pore volume of 0.80 cc/g and a collapsing strength of 15 kg. When these particles were impregnated with 20%, based on the weight of the particles, of Green Apple pH-5527 (a product of Takasago Corporation), which was based on an ester perfume, the impregnation was complete after about 15 minutes. The change in the amount of the perfume volatilized with the lapse of time was measured in the same way as in Example 5. Figure 3 shows the results. The aromatizing agent of the present invention showed an excellent effect of slow release such that 25 days were necessary for 40% release.

Comparative examples 5 and 6 The same spherical calcium silicate particles (Comparative Example 5) and EVA pellets (Comparative Example 6) as those used in Comparative Examples 3 and 4, respectively, were impregnated with 20% of the same perfume as that used in Example 6, and the change in the amount of the perfume volatilized with the lapse of time was measured. Figure 3 shows the results. 12 and 10 days were necessary for 40% release of the perfume, respectively. These rates are higher than that of Example 6.

Example 7 18 g of a porous plateform moulding (70 mm x 70 mm x 15 mm) of cellulose acetate of a combined acetic acid content of 55% was immersed in 500 ml of a 0.5% aqueous sodium hydroxide solution with stirring at room temperature for 5 minutes and dehydrated, washed and dried in the same way as in Example 5. The surface-saponified cellulose acetate moulding obtained had a pore volume of 0.7 cc/g and a collapsing strength of 15 kg. This moulding was impregnated with 18 g of a compounded perfume Kinmokusei pH-5528 (a product of Takasago Corporation) for about 40 minutes. The moulding containing the impregnated perfume did not show surface stickiness due to the perfume and maintained a satisfactory state when it was left standing at a temperature of as high as 80"C. To compare the volatility of the perfume, a plate formed from wood tips, e.g. sawdust (70 mm x 70 mm x 15 mm, a product of Takasago Corporation) was impregnated with 18 g of the above compounded perfume. Both of the above aromatizing agents were set in an air duct in position to provide the same condition and air was blown into the duct at a rate of 2.8 m/sec. Figure 4 shows the results obtained. These results also show that the aromatizing agent of the present invention show an excellent effect of slow volatility.

Claims (4)

1. A porous moulding of cellulose acetate is provided which comprises cellulose acetate having a combined acetic acid content of 50 to 58%, a pore volume of at least 0.65 cc/g and a collapsing strength of at least 10 kg and an odoriferous substance contained in the pores of cellulose acetate.

2. A porous moulding as claimed in claim 1, which has been saponified on the surface.

3. A porous moulding as claimed in claim 1 or 2, which is in the form of particles having a particle size of 0.5 to 10 mm and a sphericity of at least 0.8.

4. A porous moulding substantially as herein described with reference to and as illustrated in any of the Examples.