Phosphate fibers

Griffith chronicled in lively fashion the growth and sudden demise of an extraordinary project of the Monsanto Co. to make phosphate fibers as substitutes for the much maligned asbestoses. The object was to make materials with most of the desirable properties of asbestos, but that would hydrolyze slowly in, say, the alveoli of the lungs to form a soluble and biologically beneficial product (phosphate ions), so avoiding the tendency of insoluble aluminosilicate fibers to remain indefinitely in biological material with the attendant risk of cancer. 

The Monsanto project is said to have been canceled, despite the effectiveness and designed environmental friendliness of the products, because of the sinister reputations (not wholly deserved) of both asbestos and phosphates in the popular view. A similar problem with public perception of silicone surgical implants was noted in Section 3.5. The tenor of our times is such that much beneficial technology may be lost through litigation (or the mere fear of it) regardless of any favorable scientific evidence that is put forward. 

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All animal studies made with calcium phosphate fibers have shown that the fibers are degraded by the enzymes in living systems. To date, the phosphates have been tested as implants in the pleural or peritoneal cavities of rats. As was to be expected... 

Figure 2. The corrosion of calcium phosphate fibers at boiling temperatures. Key A, water , 0.1N...

We make a mention of phosphate fibers, or more appropriately polyphosphate fibers, that were developed by Monsanto Co. as a replacement for asbestos fibers (Griffith, 1995). Basically, the silicon atoms of asbestos were replaced by phosphorus atoms. These polyphosphate fibers were supposed to be a kind of safe asbestos fiber. However, Monsanto did not commercialize these fibers because of a possible vulnerability to lawsuits. The safety feature of polyphosphate fibers stems from the fact that they are composed of components that are constituents of the human body and are thus biodegradable. The polyphosphate fibers developed by Monsanto were similar to asbestos fibers in terms of their insulating and nonflammable characteristics. 

Griffith, E.J. (1995) Phosphate Fibers, Plenum Press, New York,... 

Griffith, Edward J. Phosphate Fibers. Topics in Applied Chemistry. New York Plenum Press, 1995. 

Alkali metal and alkaline earth polyphosphates crystallize as short chains, two to six phosphate groups per chain or very long chains with hundreds to thousands of PO3 per chain. All polyphosphates in the alkali metal and alkaline earth systems are amorphous in the intermediate chain lengths. Control of the short chain length polyphosphates, both crystalline or amorphous, is a function of R, the M2O-P2O5 ratio. The control of the chain lengths of very long crystalline polyphosphates as Maddrell s salt, Kurrol s salt, and calcium phosphate fibers is not well understood. 

If the calcium phosphate fibers grown from ultraphosphate melts are slurried with a solution of sodium ethylene diamine tartaric acid the calcium crystals can be converted to a sodium phosphate glass that dissolves very slowly yielding very long chains. 

Three possibilities exist when a salt with a polyphosphate x-ray pattern crystallizes from a melt containing an excess of phosphorus pentoxide. 1. The phosphorus pentoxide is incorporated into the polyphosphate chains converting the chains to crystalline ultraphosphates. 2. The excess phosphorus pentoxide does not enter the polyphosphate crystal structure, but forms an amorphous phase between the crystals of polyphosphate. The amorphous phase is not detected by x-ray. 3. The excess phosphorus pentoxide does not enter the crystal structure of the polyphosphate, but forms as an ultraphosphate between the crystalline polyphosphate crystals as a eutectic phase. (This latter case is precisely what happens in the calcium sodium ultraphosphate system from which calcium phosphate fibers are grown (21) and the phase diagram of Hill et. al. is obeyed as it should be.)... 

In the potassium Kurrol s salt phase system the crystalline analogues to Ca2P60i7 or CaP O i were not found by a literature search. (22) The amorphous potassium ultraphosphate systems have been studied. (23) Amorphous condensed phosphates are seldom, if ever, single compounds, but are a random mixtures of compounds and can be large and very complex. If the ultraphosphates were embedded between crystals of pure potassium phosphate fibers they would be very difficult to detect. 

This extensive matrix spalling was not observed for the other composites, implying relatively weak fiber-matrix bonding in the LlWl specimens. Weak bonding was possibly due to poor impregnation of the fibers by the matrix during fabrication, or a deficiency of the phosphate fiber-matrix binder in the near surface region of the composite. 

Titanium fiber reinforced bioactive glass Zirconia reinforced A-W glass-ceramic Calcium phosphate particle reinforced polyethylene Calcium phosphate fiber and particle reinforced bone cement... 

Calcium phosphate fiber reinforced polylactic acid... 

These focal points will be referred to from time to time throughout this work. They are the foundation on which the cornerstones of the Phosphate Fibers Project were laid. 

He was hooked. He recognized that he was incapable of knowing a polyphosphate from asbestos when the polyphosphate was properly prepared. The Director responded to Dr. Payne in much the way Dr. Payne had responded to me. There was no way to stop the Phosphate Fibers Project. We were on our way even if it was not the start of a planning year. If a project looks good enough, simple rules are made to be broken. 

No other fibrous substances approach the wondrous physical and chemical properties of these very natural serpentine minerals. In retrospect, had I known more about serpentine minerals when I initiated the Phosphate Fibers Project, it is doubtful whether I would have had enough courage to attempt to prepare a phosphate replacement analogue of these minerals. The more I learned of these fibers, the more wondrous their properties became. 

From the moment of conception of phosphate fibers, during all research and development of phosphate fibers, it was our expressed purpose to deliver a safe, useful, inexpensive mineral fiber to society. It cannot be questioned that our mission was noble. A profit motive existed a corporation ceases to exist when there is no profit, but profit motive was not the driving force behind this project. Because of our mission it would be both deceitful and cowardly to ignore safety issues that deal with natural asbestos. These issues will be considered for comparison to phosphate fibers when it is deemed necessary. If there were no safety issues a Phosphate Fibers Project should never have existed. Properties built into phosphate fibers, to insure their utility and safety, were chosen to overcome the problems associated with asbestos. The properties of the phosphate fibers must be compared with natural serpentine minerals, both negatively and positively, if this book is to serve a useful purpose. 

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