For example, the level of incorporation of calcium carbonate 0. Deep-f lighted TSEs may reach torque-limited capacity before the feeding rate limitation. Because the heat capacities of most fillers are only about half that of typical polymers, the capacity of such an extruder may actually increase as the filler loading is increased. Clay delamination was found to be improved by adding all the ingredients in the feed port, as the stresses were greatest as the polypropylene was melting, and there was no tendency to form conglomerates as occurs with CaCO3.
They concluded that the TSE would be preferred when the polymer is not susceptible to shear degradation, while the reciprocating single screw offers some benefits when fillers or fibers are highly susceptible to breakage. Deep channels are preferred with both types of equipment to facilitate easier intake of larger volumes of filler. The SPE Guide on Extrusion Technology and Troubleshooting  contains chapters particularly relevant to the processing of polymeric systems.
References 1 Grulke, E. Welsch, R. Gale, M. Rogers, M.
A comprehensive and up-to-date overview of the major mineral and organic fillers for plastics, their production, structure and properties, as well. A comprehensive and up-to-date overview of the major mineral and organic fillers for plastics, their production, structure and properties, as well as their.
Qian, B. Gale, G. Todd, D. Einstein, A. Kapfer, K. Paul, E. Vlachopoulos, J. These minerals include a number of natural products such as talc, kaolin, wollastonite, and ground calcium carbonate, as well as synthetic products such as precipitated calcium carbonate, aluminum trihydrate ATH , magnesium dihydroxide MDH , synthetic silicas, and silicates. A major need for silanes as coupling agents arose in the s when glass fibers were first used as reinforcements in unsaturated polyester UP resins. The first commercial silanes appeared in the mids.
Since then, they have become the most common and widely used coupling agents. The silicon functional group X is a hydrolyzable group chosen to react with surface hydroxyl groups of the filler to produce a stable bond, and is usually halogen or alkoxy. The silane coupling agents in commercial use are generally alkoxy-based and bear one organic group attached to the silicon center, the general formula being Y- CH2 3Si OR 3. The organofunctional group Y is tightly bound to the silicon via a short carbon chain and links with the polymer.
This group has to ensure maximum compatibility with the resin system. Bonding to the polymer takes place by chemical reactions or physicochemical interactions such as hydrogen bonding, acidbase interaction, interpenetration of the polymer network entanglement , or electrostatic attraction. The group Y may be non-functional or functional reactive ; examples of the latter are vinyl, amino, methacryl, epoxy, mercapto, etc. Most silanes are colorless or slightly yellowish, low viscosity liquids.
Both the non-functional and functional organosilanes discussed below are employed in important commercial filler treatments. Tetrachlorosilane is used to manufacture optical fibers, silicic acid esters, and fumed silica. Trichlorosilane is, in addition to other uses, the starting material for organofunctional and alkyl silanes. Commercially available organofunctional silanes are produced by hydrosilylation reactions of alkenes with hydrogen-containing silanes. Subsequent esterification affords the standard commercially available organofunctional silanes Scheme Scheme Production of organofunctional silanes.
These phases are typically organic resins e. ATH or fibrous reinforcements. The properties and effects of silanes are determined by their molecular structures. The silicon at the center is bound to the organofunctional group, Y, and the silicon functional alkoxy groups, OR.
The silicon functional groups, OR, usually alkoxy groups, can be hydrolyzed at the first stage of application, liberating the corresponding alcohol. Continuous reaction with water or moisture results in elimination of all OR groups as alcohol and their replacement by hydroxyl moieties to give silanols see Scheme Scheme Hydrolysis of trialkoxysilanes. Usually, the hydrolysis of the first OR group is the rate-controlling reaction step. The filler surface can react with the silanol intermediates and in subsequent steps these Si—OH groups react with active OH groups of the inorganic substrate, building up stable covalent Si—O—substrate bonds .
If the silane is added to an aqueous filler slurry, then it has to be water-soluble. Some silanes will be rendered water-soluble after hydrolysis and the formation of silanols. These Si—OH functions are very reactive in establishing a covalent bond between the filler and the silane. In addition to fast hydrolysis, the availability of reactive hydroxyl units on the central silicon atom significantly inf luences the reactivity of the silane. In this context, it has long been postulated that monomeric silanetriols are exclusively responsible for the activity of the silane and that these monomeric units are stable for a period of a few hours to a few days in aqueous solutions.
However, it has been proven by 29Si NMR spectroscopy that oligomeric silanes are active as well. Finally, the activity of the aqueous silane solution decreases as a result of cross-linking to give insoluble, polymeric siloxanes gel structures ; this is evident from a substantial decrease in adhesion. Knowledge of the silanol concentration and the degree of oligomerization is, therefore, important when using aqueous solutions .
In terms of devising a stable waterborne silane system, the silanol form of a silane is desirable since silanols have greater solubility and reactivity than their alkoxysilane precursors. A series of waterborne silanes with different functionalities is commercially available, and these have high concentrations of active silanol groups and are stable in water for periods of up to a year.
These silanes are considered to be free of volatile organic compounds VOC. They are particularly useful in wet processes such as grinding and milling, where VOCs are undesirable, and the mineral can be treated in situ in the aqueous process slurry. Oligomeric silanes e. Figure are commercially available.
They are low viscosity liquids with high boiling and f lash points, releasing a significantly reduced amount of alcohol . Easy handling and Fig. Besides low VOC evolution during application, oligomers may provide additional benefits, such as better wettability on the filler and the formation of a more homogeneous, defect-free silane layer on the filler surface. This can result in smaller amounts of silane being needed to achieve the same final properties. Different types of oligomers are available, ranging from homo-oligomers to various types of co-oligomers, the latter combining the benefits and properties of both silane monomers.
The rate of hydrolysis depends on the pH as well as on the type of organo- and silicon-functional groups. The silicon functional group has a significant inf luence on the hydrolysis rate. The order of reactivity is as follows: propoxy 63 64 4 Silane Coupling Agents The effect of pH on the stability of the formed silanols is different from that on the stability of alkoxysilanes. Silanols are most stable at around pH 3, and their reactivity is higher at a pH lower than 1.
Silanols condense to form oligomers and, ultimately, two- and three-dimensional networks. Silanols Silane Reactivity 0 2 4 6 8 10 pH Fig. When considering silane hydrolysis and condensation, different reactivities in different pH ranges can be expected. At very low pH, silanes hydrolyze very quickly. The formed silanols are relatively stable and, over time, form coordinated networks.
At neutral pH, silanes hydrolyze very slowly to silanols, which are unstable and condense. Thus, in both cases, there is still a slow reaction in the transition from silanes to Si—O—Si networks. These silanols are very unstable and condense very quickly to give uncoordinated Si—O—Si networks. The build-up of Si—O—Si networks cannot be controlled and the uniform coating of the filler surface becomes more difficult resulting in thicker, uncoordinated layers.
The rate of hydrolysis is also inf luenced by the nature of the organic substituent on the trialkoxysilane.
As the polarity of the organic substituent is diminished by increasing the length of the non-polar chain, as for example in long-chain alkylsilanes, the hydrolysis rate decreases. This behavior can be explained in terms of the lower solubility of the nonpolar silanes in the aqueous reaction system and the associated formation of micellar structures. Incorporating polar moieties functionalities other than alkyl generally increases susceptibility to hydrolysis. However, it is not possible to determine whether the increased rate is directly linked to the functionality of the substituent or is merely a consequence of better solubility.
Without exception, in all the studied functional trialkoxysilanes, complete hydrolysis of the alkoxy substituents to the corresponding silanols takes place within a period ranging from a few minutes to a few hours, depending on the nature of the functional group. Reactivity towards hydrolysis increases with substituent in the following order: alkyl 4. Thus, they are most effective on fillers with high concentrations of reactive hydroxyls and a sufficient amount of residual surface water. Silica, silicates including glass , oxides, and hydroxides are most reactive towards silanes.
Silanes are generally not as effective on materials such as sulfates and carbonates, although encapsulation with, for example, silica can facilitate stable silane modification even on these surfaces. As a first step, fixation of the silanol on the filler surface is accomplished through hydrogen bonding with the surface OH groups. Until the water molecule is eliminated and removed from the reaction site, this reaction is thought to be reversible.
As long as there is only hydrogen bonding, the silane can still migrate on the filler surface. The covalent [silane—O—filler] bond eventually fixes the silane on the filler surface. In theory, the silane and in the reactions that follow, the oligomers form a monolayer on the filler surface see Scheme In reality, the propensity of trialkoxysilanes for self-condensation to produce various three-dimensional networks makes the concept of monolayer coverage based on simple surface reaction of dubious value when considering this type of molecule. The most highly reactive silanols form oligomers prior to the reaction with the filler surface.
This does not normally affect the performance of the silane on the surface. Elucidation of the exact nature of the surface layers and their relationship to the coating conditions has proven to be difficult. The current understanding is that silane layers on mineral surfaces are thicker than the postulated theoretical monolayer see Figure Such layers are very complex and depend on the coating conditions used, the nature of the mineral surface, and the chemistry of the reactive functionalities present. In general, it is known that silane layers, as they are normally formed and Scheme Mode of reaction between a silanol and an inorganic surface.
The physisorbed silane is readily removable by solvent washing, whereas the chemisorbed silane is not extractable. In order to obtain maximum efficiency, uniform silane dispersion is essential and this is achieved through the high shear rates provided by the mixing equipment. Most important commercial silane-coating processes are continuous and have high throughput rates. Control over the rate of silane addition, the dwell time, and the exact temperature within the system is essential. A certain elevated temperature is required to promote complete reaction between the silane and the filler; however, an excessively high temperature may lead to a loss of the silane reactivity.
All parameters need adjustment depending on the type of silane employed. In general, the treated filler is heated after the addition of the silane to remove the reaction by-products, solvents and water, and to completely and permanently bond the silane to the filler surface. Also important in this step is the control of the by-prod- 4. Explosive limits and concentrations of the evolved alcohol should be considered and special collection systems can be installed to reduce the risk of explosions. In general, silanes need a certain time to react with the filler surface.
Accordingly, dwell times of only 2—3 minutes are common. Since the main covalent reaction is completed after about 15—30 minutes, to assure fixation of the silane on the mineral surface an additional 30 minutes should be allowed at elevated temperatures. Generally, silane loadings are between 0. Obviously, fillers that react with water cannot be treated according to this method. The slurry procedure should be considered for commercial treatment when the filler is handled as a slurry during manufacturing.
The reaction medium may be aqueous, a mixture of an alcohol and water, or a variety of polar and non-polar solvents. Alternatively, the silane can be applied as an emulsion. The silane solution or emulsion can be applied by spraying, dipping, or immersing. Removal of water, solvents, and reaction by-products requires additional steps such as setting, dehydration, and finally drying.
Silane loadings are comparable to those achieved by way of Method I. The undiluted silane is added directly to the polymer, either prior to or together with the filler. It is essential that the resin does not react with the silane prematurely as otherwise the coupling efficiency will be reduced. Typical types of compounding equipment are internal mixers, kneaders, Banbury mixers, two-roll mills, and extruders. This is mainly due to the one-step process and the lower raw material costs untreated mineral plus silane compared to pre-treated mineral , despite the fact that more silane is needed to achieve comparable performance in the finished composite.
Here, the silane is adsorbed at very high levels onto suitable carriers and then blended with the polymer and filler during compounding. In addition, an easy and safer handling method is assured. Silane loadings are comparable to those achieved by way of the in situ method. Proper selection of the mineral, silane, and production parameters will lead to optimum properties of the composite . In general, surface analysis depends on the type of organofunctional group on the silane.
To avoid the analysis of physisorbed rather than chemically bound silanes, the treated mineral can be eluted with an excess of solvent in which the respective silane is soluble. There exist several analytical methods that can distinguish between chemically bonded and physicochemically adsorbed silanes.
The untreated mineral filler should be used as a control to eliminate the absorption bands inherent to the mineral. In most cases, this method is semi-quantitative, resulting in the detection of approximate loadings of the silane on the surface [20,21]. Similar results may be obtained by means of Raman spectroscopy. Chemically bound and physicochemically absorbed silane can be distinguished by this method .
During refilling of the resulting vacancy by an outer electron, energy released can be transferred to a third electron, which leaves the solid and can be detected. By this method, two-dimensional silanecoated surfaces can be analyzed . Although it may be assumed that comparable processes take place on the surfaces of mineral fillers, AES cannot be used for their analysis since mineral fillers are three-dimensional.
Figure shows the results of AES surface analysis of a control E-glass sample. The sample was rinsed with ethanol prior to the analysis and, as a result, the elemental composition consists only of silicon and oxygen SiO2 after a few seconds of sputtering. For AES depth-profiling, the ethanol-rinsed E-glass plate was dipped in a 1 wt. The lack of homogeneity of the monomeric cationic aminosilane surface layer is confirmed by a shady SEM scanning electron microscopy image Figure In contrast, the oligomeric cationic aminosilane leads to a much more homogeneous surface. By AES depth-profiling it could be proven that the monomeric cationic aminosilane leads to an average silane layer thickness of ca.
AES line scans Figure demonstrate the resulting very homogeneous layer of the oligomeric cationic aminosilane. In contrast, the monomeric cationic aminosilane leads to silane pinholes and isolated domains. The data show 4. The samples are pyrolyzed and the volatilized parts of the silane especially those originating from the organofunctional group can be subsequently determined by GC . The results are semi-quantitative within the same system of mineral and silane; in all other cases they are only of a qualitative nature.
For example, application of an aminosilane to an acidic mineral will change its surface pH. Such changes can be monitored by titration in the presence of conventional indicators. Placing a mineral that has been treated with, for example, an alkyl-, vinyl- or methacryloxysilane into distilled water will immediately show how effective and how uniform the treatment has been through the amount of filler which f loats on the water. In another empirical method, a drop of water is applied to a pile 73 74 4 Silane Coupling Agents of the treated mineral.
The time required for the water droplet to permeate into the mineral provides an indication of the quality of the treatment. It is important that the colorant does not block any of the active sites on the mineral surface and that it spreads as homogeneously on the surface as the silane itself. The colorant needs to be soluble in the carrier. In this way, the normally invisible silane coating may be visualized; a proper treatment will lead to a homogeneously colored surface.
The list, based on experience, is not exhaustive and variations are possible. Major suppliers of silanes include Degussa Corp. The surface reactivity of many non-black fillers generally precludes strong bonding with a polymer matrix and, in some cases, leads to poor compatibility and dispersion. These filler surfaces can be made polymer-reactive if careful consideration is given to the choice of the organofunctionality of the silane. In the formulation, one part per hundred parts of resin phr of each silane indicated was introduced during compounding of phr of filler in a two-roll mill, and the composite properties were determined by standard DIN methods.
In the peroxide-cured system, all of the silanes promote significant improvements in modulus, but to different degrees depending on their relative reactivity. The methacryloxyfunctional silane is considerably more effective than the vinylsilane; this could be predicted from consideration of the relative reactivities of the double-bond moieties carbonyl vs. The aminosilane also provides a high level of filler—polymer interfacial bonding, whereas the mercaptosilane is relatively less effective compared to the methacryloxysilane. An example of a different reaction of an amino-functional silane with a modified polymer is the reaction of the amino groups with maleated polypropylene to form an imide Scheme This reaction is extensively used to couple treated glass fibers with polyolefins see Chapter 7.
The hydrolyzable groups are usually methoxy, ethoxy, or 2-methoxyethoxy. This type of functionality is used in polymers that are cross-linked by a free-radical process peroxide cure. The vinyl group is, however, not sufficiently reactive for all systems and the methacryloxy functionality is sometimes preferred, as shown in Table . The first generation of halogen-free f lame-retardant HFFR materials possessed excellent fire and smoke properties, but were mechanically weak and slow to process when compared with the PVC compounds that they were replacing.
Vinylsilane adhesion promoters make possible the high loading levels of ATH required for effective f lame retardancy, the improvement in melt processability of the highly filled EVAs, and the enhancement of the mechanical properties of the finished product. Oligomeric vinylsilanes, in addition, may provide a significantly reduced quantity of alcohol and hence lower VOC emissions upon reaction with moisture. Appropriate use of oligomeric vinylsilanes may also reduce compound viscosity and produce a smooth, defect-free surface.
They do not have the smoke and corrosive gas problems associated with other types of f lame retardants. This is the prime goal of the ATH manufacturing process. Experience suggests that large and thick particles of ATH with a low surface area are required for effective f lame retardation. When using vinylsilanes in HFFR materials, a small amount of peroxide is required to obtain good coupling. The basic formulation contained phr of ATH, 1 phr of stabilizer, and variable amounts of monomeric and oligomeric silanes and peroxide.
A co-rotating twin-screw extruder was used to produce sheets for the tests. The silane content is based on the filler; the silane was pre-blended with the EVA. Dicumyl peroxide DCP and Irganox phenolic stabilizer were used as peroxide and stabilizer, respectively. A control without silane is not included since it led to scorch. In the presence of peroxide, however, the overall picture changes dramatically. As the ATH couples with the EVA, tensile strength increases and water uptake is reduced both through increasing the cross-link density and by rendering the compound hydrophobic.
Elongation at break is not significantly affected by the presence of peroxide. Oligomeric vinylsilanes perform better than monomeric vinylsilanes, even at a lower concentration of 1. At a silane concentration of 1. As is clearly demonstrated in Table , increased silane levels reduce the risk of scorch significantly. In general, the properties achieved by the use of oligomeric vinylsilanes are 77 78 4 Silane Coupling Agents clearly superior to those achieved with commonly employed monomeric vinylsilanes, even at the lowest concentrations.
They have a wide versatility, also being used in epoxies, phenolics, polyamides, thermoplastic polyesters, and elastomers. Unlike for most other silanes, their aqueous solutions are quite stable as a result of hydrogen bonding between the silanol groups and the primary amine. An internal five- or six-membered ring is formed see Scheme The reactivity of the primary amino group has hampered elucidation of the nature of surface layers resulting from its adsorption on the filler.
The amino group itself may absorb strongly on a variety of surfaces and has also been shown to be very prone to hydrogencarbonate salt formation with atmospheric carbon dioxide. Modern analytical procedures are needed to elucidate some of the important features of these coatings; Ishida [18,19] has given a very good account of the current state of knowledge. It is directly related to the filler loading level and decreases with increasing loading. In the absence of a fine and uniform dispersion of the filler particles, agglomerates acting as stress concentrators will provide sites at which impact failure originates.
Optimizing filler dispersion would, therefore, minimize the formation of filler agglomerates and yield more homogeneous materials with improved impact properties. The polyamide-6,6 selected in the example below was a general purpose, lubricated material. The filler used was a fine calcined clay that was surface modified with 1 wt. Compounds were prepared at 40 wt. All injection-molded test samples were conditioned 24 h, 4.
Aminosilane treatment of calcined clay dramatically improves the properties of the filled polyamide-6,6. Data are not shown for nylon compounds with 40 wt. Good calcined clay dispersion in the polymer phase leads to low compound viscosities as measured by MFI and better processability. Treatment with this non-polar silane also results in reduced moisture uptake by the filler. The use of 3-aminopropyltriethoxysilane became an industrial standard for the production of reliable thermoplastic HFFR compounds.
Aminosilanes are also found 79 80 4 Silane Coupling Agents in thermoplastic, non-peroxide cross-linked EVAs, which is an alternative technology with widespread use in industry. The basic formulation contained phr of ATH, 1 phr of stabilizer Irganox , and 1. Compounds were made in a co-rotating twin-screw extruder and test specimens were produced from extruded sheets.
The presence of a carbonyl group in the molecule leads to a tendency for it to orient f lat on the filler surface under certain conditions . Thermosetting filler systems prepared from unsaturated polyesters UP , methyl methacrylate MMA , vinyl esters, epoxy EP , phenolic, and furan resins are used in many applications. It can be shown that, after pre-treatment of the filler, the organofunctional silanes cause a marked reduction in viscosity and an enhancement of mechanical properties, such as f lexural and impact strength.
This is especially evident after exposure to moisture. The organofunctional silane led to greater retention of the mechanical properties compared to the silane-free system, as shown by f lexural strength data after 6 h in boiling water. Maximum effectiveness was achieved by introducing the silane through pretreatment of the filler. A gap between the polymer matrix and the filler particle indicating debonding is visible in the absence of silane.
In the presence of silane, no gap between the resin and the cristobalite particles can be detected and the composite breaks in the polymer phase as a result of the improved adhesion. For example, in a system containing 60 wt. In addition to decreasing cost, these fillers serve to increase hardness, act as a heat sink for the exothermic curing reaction, decrease shrinkage during curing, and improve other properties, particularly retention of mechanical and electrical properties after extensive exposure to water.
Using 3-glycidyloxypropyltrimethoxysilane, the viscosity of an epoxy containing 60 wt. Here, the silane is added during rubber compounding, either neat or in the form of a dry liquid, in order to react with the silanol groups of the silica. The rubber-active group of the silane tetrasulfane, disulfane, thiocyanato or mercapto group has a strong tendency to form rubber-to-filler bonds during cur- 81 82 4 Silane Coupling Agents ing of the rubber compound . It should be noted that silane pre-treated silica is only used for technical rubber goods, and not for tires.
In particular, low volatility silanes are of great interest in the industry as they allow higher treatment temperatures and shorter dwell times increased throughput. Also, the combination of silane functionalities in a single silane molecule e. Finally, one challenge remains: an effective and commercially viable silane for filled PP is not yet on the horizon.
References References 1 Ishida, H. Skudelny, D. Ramney, M. Marsden, J. Plueddemann, E. Atkins, K. Beari, F. Arkles, B. Brand, M. Rosen, M. Coatings Technology , 50 , 70— Hanisch, H. Harding, P. Adhesion Science and Technology , 11 4 , — Ishida, H. Composites , 5, Adhesion , 79, — Garbassi, F. Colloid and Interface Science , 1 , — Bartella, J. Albers, P. Hartwig, A.
Sampson, P. Wang, G. Schofield, W. Mack, H. Plastics Compounding, Hunsche, A. Monte 5. The different ways that these additives work in filled polymers can be explained by breaking down the various mechanisms of the titanate or zirconate molecule into six distinct functions. Filler pre-treatment and in situ reactive compounding with titanates and zirconates to effect coupling, catalysis, and heteroatom functionality in the polymer melt are also discussed.
This permits coupling to non-hydroxyl bearing, and therefore non-silane reactive, inorganic substrates such as CaCO3 and boron nitride as well as organic substrates such as carbon black and nitramines without the need of water of condensation as with silanes. The thermally stable quaternary carbon structure of the neoalkoxy organometallics permits in situ reactions to take place in the thermoplastic melt. In addition, the coupling of monolayers of a phosphato or a pyrophosphato heteroatom titanate or zirconate imparts synergistic intumescence to non-halogenated f lame retardants such as Mg OH 2 and aluminum trihydrate ATH ; f lame retardance function to fillers such as CaCO3; control of the burn rate and burn rate exponent of aluminum powder rocket fuels; and extinction of the f lame spread of spalls of polymer-bound nitramines used in propellants and explosives.
Furthermore, the in situ monomolecular deposition of titanate on the surface of a particulate, such as a nanofiller, renders the particulate hydrophobic and organophilic. Under melt compounding shear conditions, the titanate assists in the removal of air voids and moisture from the particle surface, resulting in complete dispersion and formation of a true continuous phase, thus optimizing filler performance.
This may result in the creation of metallocene-like titanocene or zirconocene behavior associated with effects such as increased composite strain to failure, resulting in increased impact toughness, or enhanced polymer foamability.
Other effects to be discussed below with specific examples are related to enhanced processability, reduced polymer chain scission, shortened polymer recrystallization time, and the compatibilization of dissimilar polymers. There is a significant body of published information on titanium- and zirconiumbased coupling agents. During the period —, patents and technical papers appeared. Some detailed historical documentation with more than figures and tables is provided by the author in ref. References [2—21] are some of the technical papers and conference presentations by the author. Table provides a chemical description of the coupling agents discussed in this chapter, along with an alpha-numeric code for the titanates and zirconates invented by the author.
The alpha-numeric code is often used alone in this chapter for the sake of brevity. Table 52 indicates the designation of just a few of more than 50 commercial titanates and zirconates available from various vendors, such as Kenrich Petrochemicals, Inc. Kenrich licensee. However, Plueddemann  observed that organosilanes are essentially non-functional as bonding agents when employing carbon black, CaCO3, boron nitride, graphite, aramid or other organic-derived fibers. Hybrid titanate zirconate coupling agents, such as those containing 1 mole each of a carboxyl [function 3 ] and aliphatic isostearoyl [function 4 ] ligand and 2 moles of carboxyl [function 3 ] and acrylyl [function 5 ] ligands, are possible.
These effects are also related to the method of application of the titanate on the filler surface, as discussed below. In addition, a variety of particulate fillers such as carbonates, sulfates, nitrides, nitrates, carbon, boron, and metal powders used in thermoplastics, thermosets, and cross-linked elastomers do not have surface silane-reactive hydroxyl groups, while almost all three-dimensional particulates and species have surface protons thereby apparently making titanates more universally reactive.
C20 aliphatic mineral oil can be used as a low molecular weight model for polyolefins. Since it is non-polar and, thus, a poor medium for dispersion of most polar fillers, coupling agent effects can be more easily measured. Figure shows the effect of 0. The deagglomeration effect is apparent.
Download preview PDF. Several minerals are used for this purpose: talc, calcined kaolin, cristobalite, precipitated silica, diatomaceous earth, mica, calcium carbonates, calcium sulfate anhydrite , magnesium carbonate, magnesium sulfate, and feldspars. Natural magnetite is composed of hard, angular particles that can enhance slip resistance of polymer flooring. The use of these hollow ceramic microspheres is recommended for the formulation of very demanding formulas. Such factors seriously complicate the task of establishing sharp boundary lines between extenders and functional fillers in terms of their generic composition; however, on the performance basis they can be separated as shown in the fig Therefore, the extender fillers basically lower the formulation cost and increase the flexural modulus, whereas the functional fillers provide at least one specifically required function in the formulation.
Significant viscosity reductions have been observed through the application of the same titanate at 0. The CPVC is defined as that point at which addition of more filler to an organic phase will cause incomplete wetting due to insufficient organic binder being available to wet the additional inorganic filler surface. Figure transitions from the model f luid to polypropylene PP polymer as the organic phase and shows the f lexibility imparted to a sample containing 70 wt.
Voelkel et al. Titanates and zirconates are well established adhesion promoters, as discussed in ref. A recent example of 91 92 5 Titanate Coupling Agents bonding polyolefins to metals appears in ref. The application of increasing amounts of titanate on substrates such as CaCO3 results in significant changes in hydrophobicity, as shown from contact angle measurements with water droplets. In a recent publication by Krysztafkiewicz et al.
The highest degree of hydrophobicity was observed for silicas modified with 1 wt. The authors also observed that water was necessary for the silane to couple to the silica, while it was not needed in the case of the titanate. However, in situ coupling requires careful consideration of good compounding principles to avoid localized, inconsistent or incomplete coupling because of inadequate specific energy input low shear caused by reduced polymer viscosity induced by the coupling agent.
Localization and physical absorption of the coupling agent on the filler or fiber that results in whole segments of uncoupled particulate surfaces can be largely overcome by using masterbatches of the coupling agent see Table In order to effect monomolecular level coupling, the titanate or zirconate must be solubilized in the organic solvent, plasticizer, polymer phase or finely emulsified in water prior to addition of the filler.
If the organic phase has a high molecular weight, then sufficient shear and high mixing torque is needed to assure titanate distribution. Uniform distribution of the titanate in the dry powder ingredients or accurately dosing in the melt dictates the matching of the titanate form to that of the polymer or filler by using appropriate liquid, powder or pelletized titanates see Table Therefore, when evaluating a titanate in an unfilled or filled thermoplastic, it is imperative to compare both compounds processed at the same specific energy input.
The importance of specific energy input in relation to the dispersion of fillers during 5. Again, filler dispersion is defined as the complete deagglomeration of the filler as attritted or precipitated so as to allow all moisture and air in the interstices of the agglomerates to be replaced with a continuous organic polymer phase. One effective method for dry filler pre-treatment is to apply the neat titanate, either by airless spraying or by adding it dropwise over a period of 1 minute, to a f luidized bed of the filler as created by a Henschel-type mixer operating at low speed rpm.
The treated filler thus obtained can then be compared with an in situ treated control to test the effectiveness of the dry treatment method. This is necessary because for certain fillers, such as Mg OH 2, dilution is needed to avoid localization and uneven distribution.
The aromatic e. Currently, published efforts in metallocene titanocene and zirconocene chemistry by major polymer producers appear to be centered on olefin polymers and copolymers. Metallocene-derived HDPE and engineering plastics seemingly remain a future goal, while titanate and zirconate esters appear to be efficacious to some degree in virtually all polymers synthesized by various routes . Moreover, the titanocene or zirconocene catalysts used in the synthesis of metallocene-derived polymers do not remain in the polymer. The melt index of the control blend without titanate climbs from 17 to 38, while the value for the blend with titanate is only 24, thus indicating a significant decrease in chain scission due to the titanate.
The control melt index increas- es from 17 to The value for the blend with titanate increases only to 24, indicating a significant recombination of cleaved polymer chains. Table gives examples of filled systems for which easier processing and better mechanical properties may be attributed to this effect. System Titanate coupling agent Coupling agent effects Refs.
Figure depicts a theoretical monolayer of phosphato titanate [function 3 ] coupled to a substrate. Pyrophosphato titanates are efficacious on metal oxides such as antimony oxide, which is used in halogenated f lame-retardant systems. ATH must be loaded to a level of 64 wt. Examples of the synergisitic benefits of titanate on function 1 coupling, function 2 catalysis, and function 3 phosphato and pyrophosphato heteroatom intumescence are presented in Table In a related patent , the phosphate titanate is claimed to permit increased nitramine loadings, improve f low characteristics, and control the spread of burning propellant spalls.
For example, transparent polyolefin films containing titanate and 40 wt. Examples of work by others in the area of CaCO3-filled polyolefins are shown in Table Specific property data adapted from ref.
Polymer Titanate Comments Refs. As the amount of carbon black is increased, the resistivity is decreased. In addition, the efficiency of a fixed amount of carbon black is increased as a result of the increased dispersion offerred by the use of titanates. Yu et al. Their data show that an 18 wt.
From PTC intensity vs. Thus, it is necessary to load the polymer without losing the ability to process the compound, and then to form a part that has suitable mechanical properties. The effects of pretreating CB with KR TTS in terms of improving the low-temperature f lexibility of butyl rubber and the overall performance of a conductive isobutylene compound are described in refs.
The principal effects of the coupling agents in relation to the given application are also shown. Modifications of TiO2 with pyrophosphato- and phosphito-coordinated titanates to produce a highly functional metal oxide  and an acrylic colorant  have been described. Titanates have also been used as surface treatment agents for metal oxides in order to impart enhanced environmental stability  and in organic electroluminescent devices  for increased brightness. For example, a pyrophosphato titanate can be used to treat silica to convert it to an anti-corrosive pigment; an acrylic functional zirconate can convert TiO2 to a UV-reactive pigment; or a water-insoluble pyrophosphato titanate or zirconate, or blend thereof, can be reacted with a methacrylamide functional amine to make a water-soluble, anti-corrosive, acrylic functional organometallic additive for pigments, fillers or surfaces.
Such substrates would be compatible with water-based acrylics of high solids content. The cured resin showed good optical properties and scratch resistance.
For example, the seventh in a series of titanates synthesized by the author was a hybrid titanate KR 7 consisting of two moles of methacrylic acid and one mole of isostearic acid see Table The theory, borne out through commercial practice, was that the isostearoyl ligand would stabilize and protect the methacrylic ligands from auto-oxidation. The concluding discussion on thermally conductive thermoplastics highly filled with boron nitride and suitable for electronic packaging refers to a recent patent  with potentially significant commercial value.
Such a composition displays a thermal conductivity of at least 15 W m—1 K—1 and it is capable of being molded using high-speed molding techniques such as injection molding. It also helps to reduce the melt viscosity of the composition and allows for higher loading with the fillers. In addition, the coupling and dispersing agent may also improve the interfacial adhesion between the polymer and the ceramic fillers and thus provides better physical and mechanical properties. Appendix References 1 2 3 4 5 Monte, S. Monte, S. Louis, MO, March 21—25, References 11 Monte, S.
ACS Rubber Div. Press, a Div. Glaysher, W. Voelkel, A. Yamazaki, A. Kataoka, M. Krysztafkiewicz, A. Wang, Y. Wah, C. Galanti, A. Gummi Kunstst. Simonutti, F. Chen, C. Imahashi, T. Chiang, W. Ichazo, M. Doufnoune, R. Sharma, Y. Yu, G. Ogino, M. Hatanaka, T. Kudo, M. Manabe, T. Kuwabara, M. Murakata, T. Koike, Y. Bodelin-Lecomte, S. Young, E. Patent 5,,, Kozawa, M. Sousa, R. Vaz, C. Horibe, H.
Yang, H. Ahmad, S. Lahore , 10 4 , — Uchida, N. Chen, M. Imaoka, N. Kijima, Y. Wang, Z. Processing Soc. Fan, Q. Report, UMass, Dartmouth, Nov. Kim, C. Cho, H. Lee, S. Kitani, I. Kelley, D. Patent 4,,, Schut, J. Zhuo, Q. Rothon 6. The use of organofunctional silanes and titanates has been described in Chapters 4 and 5.
This section covers the other main approaches that can be used. For the purposes of the discussion, these additives are referred to as non-coupling and coupling.
Both types have advantages and limitations, and the differences between them are described below. Treatment of the noncoupling types is more extensive than in many other works. This is for two reasons. First, they are very important commercially. While division into coupling and non-coupling types is often based on chemical structures, this can be misleading.
As will be shown later, some modifiers can act as either non-coupling or as coupling types, depending on the formulation. The concept of reinforcement promoters, first introduced by Ancker and co-workers , and discussed later Section 6. The coverage has largely been restricted to additives that can be considered to have some form of chemical attachment to the filler surface.
This eliminates species such as glycols and some surfactants, which are only physically adsorbed. There is still a gray area, however, as some additives can function as polymer modifiers in their own right, but may also react with a filler surface. Where such filler attachment is thought to be likely, and important to the effects observed, then such materials e. The coupling effects are superimposed on non-coupling ones due solely to changes in the nature of the filler surface. The effects on processing are less clear-cut than with the non-coupling types. They usually depend on structural features other than coupling itself and can also be affected by at what point in the process the coupling is established i.
Strong coupling on its own would be expected to increase melt viscosity and adversely affect processing. While this can be observed, it is often masked by other effects. There is also the potential for changes in filler nucleating effects similar to those mentioned for the non-coupling modifiers. It was developed by Ancker and co-workers  and refers to modifiers that increase both strength and toughness. While most classical coupling agents increase strength, not all increase toughness.
Although it is little used today, the Ancker approach is useful, as it is independent of modifier structure or mechanism of action. It will be discussed further in Section 6. Anchoring to the filler is thought to proceed by salt formation with mineral fillers, or esterification with organic fillers such as wood products.
The first type of attachment is effective on fillers with basic and amphoteric surfaces, such as carbonates and hydroxides, but not so useful on acidic surfaces such as found on silicas and silicates. The carbon chain can be linear or branched. Their name derives from the occurrence of some of the higher members, notably stearic acid, in natural fats. They are mainly obtained from natural product sources, with the products containing an even number of carbon atoms being much more abundant than those with odd numbers.
Before starting a detailed discussion, some words have to be said about the approach taken here, especially with respect to the fatty acid salts. There is considerable scope for confusion and it has to be admitted that the situation is quite complex and 6 Functional Polymers and Other Modifiers by no means clearly resolved at present. The problems stem from the fact that salts such as calcium stearate are frequently used as additives in their own right, and can inf luence compound properties without having any filler surface effects.
They are also often attracted to filler surfaces and may be formed when fatty acids react with filler surfaces. It is thus almost impossible to separate out the effects of surface and polymer modification, especially as filler surface treatments based on fatty acids may split off salts into the polymer phase, while salts initially in the polymer phase may become attached to the filler during processing. For consistency, the approach taken here is to discuss these additives in terms of filler surface attachment, but it is by no means clear that this is necessary for good effects to be obtained with fatty and other carboxylic acids and their salts .
Methods of Application The method of application of the fatty acid coatings can have a large inf luence on their structure and distribution. Increases heat-deflection temperature HDT. Resists shrinkage and warpage. Enhances flexibility. Protects from thermal and UV degradation with carbon blacks. Modifying polymer properties Electrical properties can be affected by many fillers.
For example, by adding conductive fillers, an electromagnetic shielding property can be built into plastics, which are normally poor electrical conductors. Anti-static agents can be used to attract moisture, reducing the build-up of static charge. Coupling agents are added to improve the bonding of the plastic matrix and the reinforcing fibers.
Different fillers are used to lower the cost of materials. Other additives include flame retardants to reduce the likelihood of combustion, lubricants to reduce the viscosity of the molten plastic, plasticizers to increase the flexibility of the materials, and colorants to provide colorfastness. Low-aspect fillers Fillers modify the properties and molding of the compound to which they are added. If the fillers are characterized with a low aspect ratio between the longest and the shortest dimensions, the basic properties will be less changed from those of the unfilled polymer.