JPS6224546B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating chrysotile asbestos fibers in order to reduce the adverse effects associated with the asbestos fibers, and to industrial products obtained from the fibers. "Asbestos" in the present invention shall mean a group of natural silicate minerals of commercial importance due to their fibrous properties: chrysotile asbestos, which is the most diverse, has the general formula Mg ₃ It has hydrated magnesium silicate with Si ₂ O ₅ (OH) ₄ , which is characterized by the presence of magnesium hydroxide on the outer surface of the fiber. Improved tensile properties of the fiber. asbestos fibers for modifying certain physico-chemical properties of asbestos fibers such as increasing heat resistance, improving heat resistance, waterproofing of the fibers for the production of water-repellent fabrics, dispersibility of the fibers and reducing release of the fibers during handling. There are many publications regarding the surface treatment of asbestos and the use of finished asbestos-containing products. The potential health problems associated with asbestos exposure are of particular importance to both manufacturers and users of asbestos fibers. The Safety Commission recognizes that people who inhale large amounts of asbestos dust can cause disabling or fatal fibrosis of the lungs and pleura, also known as asbestosis and various types of malignant tumors of the respiratory tract. (“Asbestos”, National Safety Commission Newsletter, R&D Section, June (1974)
Year)). Asbestos is also believed to cause various types of cancer, particularly lung cancer. Because of the apparent pathogenicity of asbestos fibers, there has been some public and certain health department opposition to the use of products containing asbestos fibers. This has led to a certain amount of research into modifying asbestos fibers in such a way as to reduce as much as possible their undesirable biological effects. Various substances have been investigated that interact with the surface of asbestos fibers and reduce their hemolytic effect. Such substances include ethylenediamineacetic acid (EDTA)
Disodium salts, simple phosphates, disodium versenate, polyzenylpyrrolidone N-oxide and alumina (G.Macnab and JS
Harrington, Natuve 214, pp. 522-3 (1967)
and certain acidic polyas (RJSchnitzer and
FLPundsack, Environmental Research 3,
Includes pages 1-14 (1970). Certain of these known substances, such as EDTA, dissolve in body fluids and do not reduce the long-term hemolytic effects of asbestos. It is therefore necessary to determine substances that will adhere to asbestos and reduce its hemolytic effect. Such passivating surface treatment materials should not adversely affect the useful commercial properties of asbestos. Furthermore, it has recently been found that asbestos fibers with at least one metal molybdate (USP. 4171405) or metal tungstate (4168347) deposited on the asbestos fibers have a reduced hemolytic effect compared to untreated asbestos fibers. Served. The following facts should be understood. That is, when asbestos fibers are treated in order to reduce their cytotoxic and hemolytic effects, consideration must be given to the cost involved. This is because the cost of processing is not at a reasonable market price for any of the processes developed so far. One of the drawbacks of the prior art of treating asbestos fibers to reduce hemolytic effects as described in U.S. Pat. Nos. 4,171,405 and 4,168,347 is that such treatments generally have the following disadvantages This includes carrying out the process in an aqueous medium. The disadvantage is that the moisture must be removed after treatment, and the treatment costs are increased to the point that the treated asbestos fibers are washed and then dried. This is to the point that asbestos fibers that have not been subjected to the above-mentioned treatments have not been commercialized to date due to the high costs required for their production. Another feature in addition to the cost of the fibers mentioned above is that the cost of the molybdenum and tungsten salts to be used is relatively high, increasing the cost of asbestos fibers so treated. Therefore, it is highly desirable to have modified asbestos fibers with reduced hemolytic and cytotoxic effects, as well as a method for commercially producing novel fibers at reasonable cost. The present invention thus provides novel chemically modified asbestos fibers containing 0.5 to 5% by weight of phosphate groups fixed to the asbestos fibers. The present invention also provides a method of treating asbestos fibers by depositing phosphate groups on at least a portion of the asbestos fibers. Asbestos fibers thus treated were found to have reduced hemolytic activity as demonstrated by using red blood cells and reduced cytotoxicity as demonstrated by using the rat pulmonary artery macrophage test. Served.
Furthermore, the phosphate fossil cotton fibers of the present invention have an unexpectedly high degree of freedom that correspondingly increases the drainage rate in aqueous slurries of products containing asbestos fibers, such as in the manufacture of asbestos-cement products. Further improved phosphate fossil cotton fibers can be obtained by subjecting the thus obtained phosphate fossil cotton fibers to a heat treatment at 300 to 500°C. Surprisingly, this heat treatment reduces the cytotoxicity of the phosphate fossil cotton fibers of the present invention, whereas when ordinary asbestos fibers are heated to temperatures of about 500°C, the toxicity of the fibers increases substantially. Report that (Hayashi, H.Envir.Health
Persp. 9: pp. 267-270 (1974). A feature of the novel phosphate fossil cotton fibers of the present invention is the absence of a characteristic peak at 1021 cm ^-1 , which is derived from the reaction of asbestos fibers with phosphate salts in an aqueous medium as disclosed in U.S. Pat. No. 3,535,150. It is one of the three characteristic peaks of phosphate fossil cotton fibers or untreated asbestos fibers obtained by
^-1 , has characteristic peaks at 1021 cm ^-1 and 954 cm ^-1 . In other words, the novel phosphated fibers of the present invention have an infrared spectrum with virtually no absorption in the range 954-1080 cm ^-1 . A feature of the invention is also the incorporation of phosphate-containing asbestos fibers into industrial products, thereby avoiding the health hazards normally associated with manipulating asbestos fibers prior to incorporation of the fibers into industrial products. , thus imparting to such industrial products the inherent safety factor of the novel phosphated fibers of the present invention. According to the invention, asbestos fibers contain phosphate groups.
Processed to deposit 0.5-5% by weight. More particularly, the method comprises contacting asbestos fibers with a circulating dry vapor of a phosphorus compound selected from the group consisting of phosphorus oxychloride and phosphorus pentachloride in an inert atmosphere that is non-reactive with the phosphorus compound vapor. As a result, some of the terminal hydroxyl groups bonded to magnesium atoms are converted into phosphate groups, and the amount of phosphate groups depends on the fiber being treated.
It is 0.5 to 5% by weight. The method of the invention can be carried out under normal temperatures and pressures. The invention will be more easily understood by referring to the drawings. FIG. 1 is an illustration showing the interconnected parts for use in carrying out the method of the invention; FIG. B is an infrared absorption spectrum obtained by treating asbestos fiber with phosphorous oxychloride according to the present invention and then subjecting it to heat treatment; FIG. 3 is an infrared absorption spectrum In the figure, C is the infrared absorption spectrum of natural and untreated asbestos fibers,
D is an infrared absorption spectrum obtained by treating asbestos fibers in an aqueous medium with NaH ₂ PO ₄ . The term "asbestos" as used in the present invention is intended to apply to chrysotile asbestos, which is the most important of the natural fibrous silicates and represents approximately 95% of asbestos production worldwide. and the phrase "asbestos fibers" is intended to apply to commercial fibers of grades 2 to 7 (Kubek standard). The phosphorus compounds chosen are those that readily volatilize at room temperature and of all phosphorus compounds only phosphorus oxychloride and phosphorus pentachloride are suitable. In fact, the vapor of the phosphorus compound is obtained through a non-reactive drying gas, whereby the dry vapor of the phosphorus compound is conveyed for reaction with the asbestos fibers. The amount of phosphorous oxychloride or phosphorus pentachloride gas used will vary depending on the amount of asbestos fibers being treated and will vary depending on the amount of phosphate bound to the asbestos fibers. For example, for 50 g of asbestos fibers placed in a reaction column, a stream of dry nitrogen of about 2 per minute is passed through a bottle of phosphorous oxychloride for 20 minutes, whereby 4-8 ml of phosphorous oxychloride comes into contact with the asbestos fibers. Modified asbestos fibers are thus obtained having 0.5-1.5% by weight of phosphate groups attached to the asbestos fibers. The amount of phosphorus compound in vapor form that contacts the asbestos fibers can be increased or decreased by increasing or decreasing the temperature of the phosphorus compound through which the inert carrier gas is passed. In fact, the reaction takes place in a rotating vessel 10 having an inlet 12 and an outlet 14 and a mixing blade 36 mounted on the wall. Rotating means are not shown. Inlet 12 and outlet 14 are connected to wall 18
It is glued to the perforated tube 16 which is closed in the center of the tube by. Nitrogen container 20 with pressure gauge 22
The flow of nitrogen is adjusted from the conduit to the containment vessel 26 of sulfuric acid 26A under the desired pressure, thereby dehydrating the nitrogen gas, and then dehydrating the dehydrated nitrogen gas to the phosphorus oxychloride 30. The solution is led to a conduit 27 in a closed container 28 . As pressure increases within the containment vessel 28, phosphorous oxychloride vapor is directed from the conduit 32 to the central inlet 12 of the rotating vessel 10. The phosphorus oxychloride vapor spreads out of the opening 16a in the central tube 12, thus coming into contact with the rotating asbestos fibers 34, and the unreacted phosphorus oxychloride reacting through the opening in the second part of the central tube 16. It flows out from the container 10. If desired, unreacted phosphorus oxychloride is recycled. Further improved phosphated fossil cotton fibers can be obtained by heating the phosphated fibers at temperatures of 300-500°C. It will be appreciated that the illustrated apparatus may be easily modified without departing from the concept of carrying out the reaction of the present invention. The main advantages of the novel process of the present invention are as follows. That is, the present reaction is carried out under dry conditions, whereas in the prior art means the reaction is carried out in an aqueous medium and therefore costs money for the energy required to remove the water after the reaction is complete. be. It has been found that the phosphates containing asbestos fibers obtained by the process of the invention not only have increased flexibility but also have reduced cytotoxic and hemolytic effects. Fibers treated according to the present invention and phosphate fossil cotton fibers obtained in an aqueous medium according to the teachings of US Pat. No. 3,535,150 were subjected to comparative tests to determine their cytotoxic and hemolytic effects. Other aspects of the invention are as follows. That is, the novel phosphate fossil cotton fibers reduce the usual hazards associated with handling asbestos fibers prior to being incorporated into industrial products, and this advantage therefore extends to the industrial products obtained therefrom. This means that it will be reflected in the The modified asbestos fibers obtained according to the invention can be incorporated into certain products and replace unreacted asbestos fibers, such as wallboards, pipes, plates,
Mention may be made of asbestos-cement products such as roof tiles, friction materials such as brakes, brake pads, clutch coatings, paper supports, yarn and textile materials, gasket materials, felts for roofing or floor linings, and insulation materials. Biological Testing The chemically modified phosphate fossil cotton fibers of the present invention, which retained their fiber structure, were tested for the degree of improvement in their cytotoxic and solution action. All were compared to samples of untreated chrysotile asbestos fibers and phosphate fossil cotton fibers obtained according to US Pat. No. 3,535,150. The test was conducted in the following manner. Hemolysis Phenomenon For each experiment, whole blood was obtained from the inferior vena cava of two ether-anesthetized adult male Long Island rats (250-300 g/body weight). The obtained whole blood was immediately suspended in 400 ml of Veronal buffer solution (290±5 mOsm) with a pH of 7.28. Red blood cells were washed three times and 4% by volume of rat red blood cells (RBCs) were prepared in Veronal buffer. Veronal test of the asbestos sample was carried out using a Dounce tube.
Suspended in 12.5 ml of buffer. The concentration of fibers investigated was varied in the range 100-1000 μg/ml. The dispersed fiber suspension was added to a Falcon tube containing 12.5 ml of RBC suspension (final concentration of RBC: 2%).
) A suspension of dispersed fibers was poured into 30 ml. The flask was shaken at 37°C in a Dubnoff metabolic shaker. Three ml samples were taken from each tube and control after 15, 30 and 60 minutes of shaking. Samples were centrifuged for 5 minutes to pellet phantom cells and intact RBCs. Dilute 1 ml of supernatant with 3 ml of Veronal buffer and test at 541 nm.
The absorbance at was measured. Add Triton X- to a 2% suspension of RBCs in distilled water.
Complete hemolysis was obtained by adding 100 ml. Cytotoxin Male Long-Evans rat with black head (250-300g/body weight)
were killed by intraperitoneal administration of an overdose of pentoparbital sodium salt. After tracheostomy, lung lavage was performed continuously in situ with calcium and magnesium-free Hanks balanced salt solution supplemented with glycol (1 g/). Free lung cells (> ¹⁰⁷ cells/rat) were isolated by low speed centrifugation and isotonic on ice.
Resuspend in a solution of NH ₄ Cl for 10 minutes. This step was introduced to eliminate contamination by RBCs. After continuous washing, cells (>95% macrophages)
The cells were counted with a hemocytometer and the viability (93-97%) was evaluated by the trypan blue test (0.4% solution). Unless otherwise noted, all fabrications were performed at 4° C. and with sterile raw materials. Then cells (10 ⁶ cells/2.5 ml of medium) were
At 37°C in a silicone-coated glass vial.
Shake for 24 hours. Shaking was carried out in normal air and the humidity in the shaking chamber was maintained at around 80%. Alveolar macrophages were incubated with 10 mM _CaCl2 and
10mM _MgCl2 , 2mM L-glutamine, 4%
(v/v) heat-inert fetal bovine serum and sterilization filled with antibiotics (initial PH: 6.8 at 37°C)
Shake in MEM medium (Hank's salts). Each fiber material was autoclaved at 121°C for 45 minutes prior to its use and then Dounced.
Gently resuspend in sterile MEM medium with a glass homogenizer. Aliquots up to 250μ/ ¹⁰⁶ cells (10, 40 and 100μg/shaking medium)
ml) was selected for analysis. After 24 hours of shaking, the shaken medium without cells was collected for analysis and analyzed for: - Cell viability (intact membranes) - Lactate dehydrogenase or LDH (cytoplasmic excretion) - B -N Acetyl Glucose Aminidase, or B-NAG (Lysosomal Damage) All spectrophotometric analyzes were performed with a dual beam spectrometer. The following contents can be understood from Table 1. That is, contact of untreated chrysotile or NaH ₂ PO ₄ treated chrysotile with red blood cells (RBCs)
yielding a degree of hemolysis of 82%, 72% and 57% compared to control, while POCl ₃ treated fibers contact
After 15 minutes, the degree of hemolysis was 16%. At the same time, the table shows that it affects the parameters of pulmonary macrophage response, which are widely adopted as indicators of cytotoxicity:
Viability, and enzyme leakage after exposure to mineral fibers. At all treatment levels, all parameters show a clear reduction in the cytotoxic effect obtained by POCl ₃ -treated fibers when comparing the effect obtained by untreated or NaH ₂ PO ₄ -treated fibers. These data must be considered in the light of the determination that there is a good correlation between the hemolytic power, the effect on macrophages and the fibrogenic action of asbestos-containing mine dust (Allison, A.
C. et al., 1977. Ann.Rheum.Dis. 36 (Suppl.)
8). Furthermore, it has been shown that there is a correlation between the cytotoxic effects of mine dust and their ability to reduce mesothelial tumors (Chdmberldin, M. et al.
1978, Br.J.Exp.Patr. 59 :183-189).

【table】

[Table] After treatment with POCl ₃ treated fibers, the surface treatment of biological effects observed in the infrared absorption spectrum
It is noteworthy that this is related to the disappearance of the characteristic absorption peak at 1021 cm ^-1 . This phenomenon was discovered when chrysotile was subjected to ball milling to obtain short fibers for experimental purposes.
Selikoff) et al. (J. Toxicol.
Env. Health 4:173–188 (1978). The produced fibers have much less hemolysis, and this is consistent with the infrared absorption spectra data, precisely the change in the data at 1021 cm ^-1 . Therefore, both the two fundamentally different methods of modifying fibers, mechanical and chemical, have a biological effect associated with the change in the peak at 1021 cm ^-1 (±2 cm ^-1 ). The biological activity is clearly related to the structural characteristics of chrysotile, which exhibits an absorption at this wavenumber according to the infrared absorption spectrum. Therefore, either physical or chemical treatment results in a reduction or disappearance of the absorption feature of about 1021 cm ^-1 in the infrared absorption spectrum, which results in a substantial change in the cytotoxic effect of such treated fibers. Contrary to mechanical methods, which lead to a significant increase in the fibrous structure of chrysotile and a concomitant decrease in the physical activity of the product, treatment with POCl ₃ inactivates the fibers but essentially destroys its fibrous structure. will not cause damage. Examples of production of modified asbestos fibers are shown below. Example 1 Asbestos fiber manufactured as a sample (grade 4T30
50g (Qubec standard) in a plexiglass cylinder (30cm x 12cm) sealed at both ends.
It was installed inside a tumbler made of. Inside the cylinder, there are a number of fixed blades as shown in FIG. Stainless steel tubing passes through both ends of the cylinder. Through the first set of holes in the tube,
Gas vapor is released inside the tumbler and is present through another set of holes at the other end of the tube. The tumbler is rotated by conventional mechanical equipment at a speed of 33 RPM. A flow of dry nitrogen (2/min) controlled by bubbling through the sulfuric acid bottle is introduced into the phosphorus oxychloride (POCl ₃ ) bottle at room temperature. The phosphorus oxychloride vapor is conveyed in a rotating tumbler with a stream of nitrogen, thus providing very discontinuous contact of the phosphorus oxychloride vapor with the fibers. Processing is carried out until approximately 4-8 ml of phosphorous oxychloride has been used. The fibers are then purged with nitrogen only for a few hours and finally removed from the tumbler and then placed in a humid chamber overnight to hydrolyze excess chloride. Analysis of PO ₄ content in treated fibers (Chemical Ardysis Volume 8 DF Boltz ed. Method D38
(1958) found that amounts between 1.5 and 5% by weight of PO ₄ were fixed on the fibers. Example 2 The phosphated fibers of Example 1 were divided into two lots. One lot was heated in an oven at 325°C for 1 hour and then all fibers were kept in the oven at 325°C. Infrared absorption spectroscopy was performed separately on untreated asbestos fibers, phosphate fossil cotton fibers according to the method of US Pat. No. 3,535,150, and asbestos fibers obtained according to Examples 1 and 2 of the present invention. The presence or absence of related peaks is shown in Table 3.

[Table] The phosphate fossil cotton fiber of the present invention is 1021cm ^-1
It is clear that it is characterized by the disappearance of the characteristic peak at 1021 cm ^-1 which is observed for untreated asbestos fibers and asbestos fibers phosphated in aqueous medium.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram for implementing the method of the present invention, and FIG.
The figure and FIG. 3 are infrared absorption spectra. 26A...sulfuric acid, 30...phosphorus oxychloride.

Claims (1)

[Scope of Claims] 1. A method for producing modified chrysotile asbestos fibers containing 0.5 to 5% by weight of phosphate groups, comprising phosphorus oxychloride and phosphorus pentachloride under drying conditions and in an atmosphere inert to phosphorus compounds. contacting the chrysotile asbestos fibers with the vapor of a phosphorus compound selected from the group consisting of the following while stirring the fibers, whereby a part of the hydroxyl groups of the chrysotile asbestos fibers are replaced with phosphate groups, and the phosphate groups are replaced with phosphate groups. A method for producing modified chrysotile asbestos fibers, wherein the amount is from 0.5 to 5% by weight of the fiber. 2. The method of claim 1, wherein the source of the phosphorus compound is phosphorus oxychloride. 3 Approximately 0.2 to dry chrysotile asbestos fiber
A phosphate fossil cotton fiber having phosphate groups bonded to chrysotile asbestos fibers in an amount of 5% by weight, the phosphate fossil cotton fibers being capable of phosphating untreated chrysotile asbestos fibers as well as chrysotile asbestos fibers in an aqueous medium. 1021 cm ^-1 obtained by infrared absorption spectroscopy of the phosphate fossil cotton fiber thus obtained.
The phosphate fossil cotton fiber is characterized in that there is no characteristic absorption peak.