In fillers & reinforcements, the action is at the interface.

Better understanding of the interactions between fillers, reinforcements, surface-modifying or coupling agents, and matrix resins bas been the aim of considerable research lately, as indicated by several papers given at two recent conferences-the big annual meeting of SPI's Composites Institute in Washington, D.C., and the SPE ANTEC in Montreal. Some of the topics covered included the relative cost-effectiveness of viscosity-reducing surface treatments on alumina trihydrate (ATH) of different particle sizes; effectiveness of different grafted polyolefins in coupling glass and PP; surface-treated microspheres as polymer blend compatibilizers; reground thermosets as low-cost fillers in polyolefins; property enhancement through coupling of natural cellulose-derived fillers in thermoplastics-including recycled materials; and a simple, new method of calculating how much couplant is just enough.

In addition, the following news report includes several new products that have come to our attention recently, including developmental ATH grades, high-strength microspheres, ceramic fibers that are synergistic' with glass, premium talcs and calcium carbonates from a new specialty supplier, and novel friction materials. There's also new information on the effectiveness of a wetting agent in permitting higher ATH loadings in SMC.

FLAME-RETARDANT FILLERS

This year, Alcan Chemicals, div. of Alcan Aluminum Corp., Cleveland, began full-scale production of Onyx Premier WP-31 white ATH. This product offers high whiteness and translucency in cultured marble and onyx. Average particle size is 35-45 microns. The company plans to expand its range of high-purity white ATH to include ground and fine-particle precipitated grades for FRP, wire and cable, and other plastics applications.

Some interesting clues to achieving maximum cost-effectiveness while maximizing ATH loadings in unsaturated polyester were present by Solem Div. of J.M. Huber Corp., Norcross, Ga., at the SPI composites conference. As shown in Fig. 1,180-phr mixtures of an unmodified coarse ATH (Solem's SB432, 8.6-micron average particle size) and an unmodified fine ATH (Solem's Micral 932,2-micron APS) produce lower viscosities than 180 phr of either ATH alone. A minimum is achieved at a 6OC/40F ATH ratio, where viscosity is 50-60% lower than with either single component.

Solem researchers find it interesting that the average particle size in the lowest-viscosity 6OC/40F mixture is 2.8 microns, and the percentage of particles below 1 micron is 25%, vs. 2.4% for C-ATH alone and 29.6% for F-ATH alone. This seems to contradict the conventional wisdom that often blames the fines' content of fillers for undesirably high compound viscosities.

By contrast, the data suggest that filler packing is optimized with some fine and some coarse articles. The presence fine particles has another advantage, Solem notes, because it is well known that flame-retardant efficiency increases as ATH particle size decreases.

Figure 2 shows experiments in surface modification with the 6OC/40F ATH blend. Solem ran series similar to that in Fig. 2 with five different surface treatments and found in all cases that treating just the coarse ATH gave greater viscosity reduction than treating just the fine ATH, and treating both gave the lowest viscosity of all. The authors suggest that processors should weigh the increase in cost for treating both filler fractions, rather than just the coarser ATH, against the incremental viscosity reduction and the possibility that offers of higher filler loadings.

Incidentally, Fig. 2 shows results with a developmental surface treatment that yielded 15-20% lower viscosity than two of the Solem's commercial treatments. A second developmental treatment yielded a further 20% viscosity reduction compared with what is shown in Fig. 2.

These data are supported by new data from BykChemie USA, Wallingford, Conn. Experiments in Germany with a variety of ATH particle sizes in low-shrink polyester SMC showed that new Byk W 995 organic wetting agent, introduced last year (see PT, April '90, p. 159), increased by 27-29% the amount of filler that could be added while maintaining the identical flow rating (by the Renault method).

All compounds contained more or less the maximum amount of filler that could be added while maintaining complete wetout of the 25% glass loading. As shown in the table, more of a coarser ATH could be added than of a slightly finer grade; however, the highest loading (and oxygen index) was obtained with a blend of coarse, medium and fine particles. Impact and flexural strengths and flex modulus were similar for all formulations.

NEWS IN MICROSPHERES

The latest from PQ Corp., Valley Forge, Pa., is development of Q-Cel hollow microspheres strong enough to survive high-pressure airless spray systems, such as those for PVC automotive underbody sealants and syntactic-foam cores for FRP laminates. New single-cell borosilicate spheres include the following:

* Q-cel 636, with an effective density of 0.35 g/cc and average particle size of 55 microns, has a crush strength of 1500 psi.

* Q-Cel 640-0.42 density, 52 microns APS, 2000 psi crush strength.

* Q-Cel 650-0.48 density, 48 microns APS, 3000 psi crush strength.

Priced around $1.39/lb tl, they're said to be oleophilic and easily dispersed.

A very interesting study suggesting that a filler or fiber can serve as an interphase compatibilizing agent in immiscible polymer blends was presented earlier this year at the SPI composites conference. Researchers Hatsuo Ishida and Natalia Scherbakoff of the Dept. of Macromolecular Science at Case Western Reserve University, Cleveland, presented what they believe to be the first systematic study of this possibility.

The objective of the study was to give both polymer components of the blend-in this case, nylon 6 and polypropylene-the opportunity to interact independently with the surface of the same filler particle. This was done by means of silane-treated solid glass beads. The authors noted that an untreated filler will tend to have a different degree of interfacial tension between itself and each polymer component of the blend; hence, one of the polymers will have a higher tendency to be present at the filler's surface than the other (in this case, the nylon more than the PP). However, a coupling agent was chosen with specific reactive groups to give each polymer an equal tendency to interact with the filler surface.

While balanced adhesion of the nylon and PP was obtained, the authors noted that "adhesion alone does not lead to surface compatibilization. Both polymers must be present at the filler surface in such a way that they interact with each other."

Evidence of such interaction, or true compatibilization, was obtained in different ways. One was a distinct decrease in crystallinity for the blend with treated filler added-much more than was obtained by adding untreated filler. This was about the same level of crystallinity as was measured on a bead-filled nylon/PP blend compatibilized by means of maleic anhydride grafting of the PP. Note that adding filler significantly reduced the crystallinity of that chemically compatibilized blend, but surface treatment on the filler had no effect.

Another sign of interphase compatibilization at the

Another sign of interphase capatibilization at the filler surface viscosity than an untreated filler; but for blends the behavior is the opposite, because viscosity increases with compatibilization, owing to reduced interfacial slippage. This was indeed observed with silane-treated beads in nylon/PP, where the viscosity was elevated into the same region as that of the unfilled nylon/maleatedPP blend.

REINFORCEMENTS

A new version of its Fiberfrax ceramic fiber reinforcing filler has been introduced by Carborundum Co.'s Fibers Div., Niagara Falls, N.Y. Fiberfrax 122S is a developmental product with an average diameter of 5-10 microns, compared with 2-3 micron diam. for standard Fiberfrax. This large diameter tends to decrease fiber entanglement, thus improving dispersibility, according to Carborundum's reinforcement market manager Margery J. Wirtner.

This product also has been specially processed to remove 20-25% more nonfibrous particulates than in other Fiberfrax grades, yielding more reinforcing fibers per pound and a longer average aspect ratio of 30-50:1. Also, the product is surface treated for dispersibility and coupling to phenolic, epoxy, nylon, melamine and polyurethane.

Wirtner reports "synergistic" enhancements of reinforcing behavior from blends of this fiber with 1/4-in. chopped fiberglass. In phenolics at a 40% total loading, the fiber blend showed up to 30% higher flexural strength and 55% higher flex modulus than was obtained with 40% fiberglass alone (properties were also higher than with just 40% Fiberfrax). In tests of wear resistance, 40% of EF 122S alone showed only 280/o as much wear as 40% fiberglass, but a blend of both fibers (40% total) readditional 32%.

Wirtner also reports that milled Fiberfrax EF 119 is beginning to find acceptance in cast urethane applications where wear resistance is more important than reinforcement. Grade EF 119 has an aspect ratio of only 10:1, but it reportedly disperses easily, allowing higher loading levels of up to 50%. Addition of only 10% EF 119 is said to cut wear by half.

BP Performance Polymers Inc., Hackettstown, N.J., has introduced two new adhesive polymers for use as coupling agents in glass-filled PP and also as compatibilizers in alloys. Polybond 3001 ($1.20/lb) and 3002 ($2/lb) are maleic anhydride-grafted BP's with 5 and 7 MFR, respectively. BP presented a paper at ANTEC showing that MAH-grafted PP is a more efficient coupling agent for glass fiber than is acrylic acid-grafted PP, also available in BP's Polybond series.

Much has been written about fiberlength degradation in injection molding of glass-filled compounds. However, an unusually revealing investigation into the subject was reported at the SPI composites meeting by Dr. Bernard Sanschagrin, P. Ehrardt and B. Fisa of the Mechanical Engineering Dept. at the Ecole Polytechnique de Montreal. They injection molded 2-3 mm test plaques of 30% long-glass (1/2 in.) reinforced PP on an 80-ton machine, then burned off the polymer and analyzed the fiberlength distribution with an image-analysis instrument.

As shown in Fig. 3, 60% of the total fiber-length degradation occurs in the screw, while about 20% takes place in the check valve, 5% in the nozzle, 10% in the sprue, and less than 5% in the runner, gate and mold. Slightly less degradation is seen in Mold II, which has a 37.5% larger sprue diameter and more than 11 times larger gate area than Mold I.

Other data show that adding a spacer ring to the check valve in order to more than triple the ring gap does indeed reduce glass breakage, but the final result is virtually the same unless the nozzle diameter is also increased and even then the improvement is relatively small. Some ability to reduce glass breakage by reducing screw speed and injection speed and increasing nozzle temperature were also demonstrated. Increasing fiber concentration above 30% resulted in lower average fiber length in molded parts.

MISCELLANEOUS FILLER NEWS

Six new lines of specialty fillers are available from Polar Minerals, Inc., a six-month-old firm in Lilburn, Ga. Polar specializes in premium-grade talcs, calcium carbonates and other mineral pigments, which are processed domestically from imported ores.

High purity, specialty fine grinds, and unusually high aspect ratio in platy talcs are special features claimed. The talcs are said to be tremolite (asbestos)free and the calcium carbonates free of crystalline silica. Both are of sufficient purity for use in cosmetics, according to the company. Pricing reportedly is competitive with other premium grades.

Polar's first processing facility, with 150-million-lb/yr capacity, is due to start up next month near Mount Vernon, Ind. Rigorous SPC/SQC will be applied to maintain strict product uniformity, says Polar president Joseph Keating, former owner of Solem Industries before it was sold to J.M. Huber Corp. Polar's products are stocked and sold by two sister companies, Delta Resources, located at the same address in Lilburn, and Kish/Crosby, Inc. in Cleveland.

Among Polar's introductory line of products are 8100 Series calcium carbonates, described as white grades in four grinds with median particle sizes from 0.7 to 7 microns and dry brightness ratings from 92 to 97. Three of those grinds are available in a coated form (8100C Series) for easier dispersion and flow and improved acid and moisture resistance. Also available is a standard calcium carbonate 8600 Series with lower brightness (80-84 rating). Three grades have median particle sizes of 37 microns.

Polar talcs include a 9100 Series of three white grades with median particle sizes of 1.9 to 10 microns and dry brightnesses of 93-96. Also offered is a highly platy 9600 Series of "performance talcs" in three grades with median particle sizes of 3-10 microns and 82-86 dry brightness ratings. The standard platy talc 9400 Series includes three grades of 10-20 micron median particle size and 79-83 dry brightness.

New surface-modified silicas are in advanced development at Bums & Russell Co., Baltimore. Two products, designated F-20OX and F-40OX, are experimental versions of existing F-200 and F-400 products, with new surface treatments that offer promise of higher loadings. F-20OX will be in the minus 70-75 mesh range and F-40OX will be minus 42-45 mesh.

Nyco Minerals, Inc., Willsboro, N.Y., is introducing a new nonfunctional surface treatment, which can be used on any of its Wollastokup, Wollastocoat, Flakeglas, ATH Nycoat, and Micacoat products. This noncoupling treatment is a thermally stable, aromatic hydrophobe designed to improve dispersion and wetout while displacing moisture from the filler surface. One new product incorporating this treatment is 325 Wollastokup 10734, a 325mesh grade of wollastonite, which has been used in polyolefins and nylon 6 and 66.

In addition, Nyco is offering two unusual new products for friction applications such as brake pads. American Tripoli, Inc., Seneca, Mo., a subsidiary of Nyco, produces Tripoli, a mildly abrasive mineral used to polish and buff decorative metals. Now, Tripoli is being used together with Nyco's Nyad G Wollastokup 20204 (a high-aspect-ratio, surface-treated wollastonite) in brake pads. The wollastonite provides reinforcement, while the Tripoli permits the compound to scour or scrub the mating metal surfaces, keeping them clean and polished without scoring, thereby providing a fresh solid surface on which the brake pad or block can act.

Another new product for brake pads and similar friction products is Promaxon D, a synthetic hydrated calcium silicate produced by Promat B.V. in Holland, which Nyco is representing in North America. Spherical-particle Promaxon is said to be a safe, nontoxic asbestos substitute with high-temperature resistance and ability to reduce brake noise. It costs around $3/lb.

Reground thermosets as low-cost fillers in thermoplastics? Apparently there's interest in this area on the part of polyolefin recyclers, says David Graham, research associate at OwensCorning Fiberglas Corp.'s Technical Center in Granville, Ohio.

At the SPI composites meeting, he and Ralph Jutte of OCF presented data on properties of reground polyester/glass SMC in PP. Blends of 15-30% coarse and fine SMC regrind in PP yielded tensile, flexural, impact and HDT properties equal to or better than those of natural PP, though elongation and unnotched Izod impact were significantly reduced. These compounds were able to match or exceed the properties of 9% glass-filled PP, except in tensile or flexural strength and Izod impact.

Several papers were given at the recent ANTEC meeting on the ability of coupling agents to improve properties of natural organic fillers in polyolefins. For instance, Southeastern Reduction Co., Valdosta, Ga., and the Center for Research in Pulp and Paper at the Universite du Quebec, Trois-Rivieres, showed that blends of pecan-shell and peanut-hull flour (from Southeastern Reduction) could be surface modified by grafting to a small amount of HDPE using maleic anhydride and dicumyl peroxide. This reportedly resulted in cost-effective reinforcing properties.

Improvements were also reported in HDPE filled with treated wood fibers (either paper pulp or wood flour) by R.G. Raj and B.V. Kokta of the same research center in Trois-Rivieres, Quebec. Wood fibers were treated with a special isocyanate from BASF Corp., silane, or a combination of maleated PP and stearic acid.

Property improvements were also observed by D.J. Olsen of Eastman Chemical Co., Kingsport, Tenn., using maleated PP as a coupling agent in wood-flour/PP compounds. Olsen noted, however, that both acid number and molecular weight of the maleated PP are critical to its coupling effectiveness.

Wood fibers from paper pulp can be treated with phenol-formaldehyde resin to provide improved reinforcing of recycled HDPE/PP mixtures, according to research presented at ANTEC by H. Chtourou and B. Riedl of the Dept. of Wood Sciences and A. Ait-Kadi of the Dept. of Chemical Engineering at Laval University, Ste-Foy, Quebec. Recycled HDPE containing 4.7% PP was supplied by Transplastek Inc., St-Bruno, Quebec.

HOW MUCH COUPLANT IS

ENOUGH?

Coupling-agent concentrations for fillers and fibers are generally determined by empirical means. Mere has been no exact method of calculating the amount of couplant needed, except for published data covering the case of pure silica treated with silane. At the SPI composites meeting, consultant Thomas H. Ferrigno of Improde, Trenton, NJ., proposed a simple variant of the oil-absorption test to help solve this problem.

His approach is based on the theory that the "optimum couplant concentration defines optimum dispersion and the most efficient packing of particles." When the volume fraction of a fixed weight of completely wetted filler in a compound is plotted against couplant concentration, says Ferrigno, a distinct peak is observed, corresponding to the optimum couplant concentration for most efficient particle packing. If either too much or too little couplant is present, greater than the minimum possible spacing between particles will result. His test method, described in the paper, involves working measured amounts of a liquid into a preweighed mass of filler until all the filler is just wetted, indicated by the first appearance of a slight gloss on the kneaded cake of material.

The "surrogate liquid," which substitutes for resin, should have a solubility parameter similar to that of the intended resin-examples could include polybutene for polyolefins, chlorinated paraffin for PVC, and polyester plasticizer for PET or PBT. Varying amounts of a "concentrate" of 10% couplant in the same surrogate liquid are added during the procedure until the optimum couplant concentration in the "compound" is identified by maximum volume fraction, or "packing fraction."