COLLOIDAL MICROCRYSTALLINE CELLULOSE AS A

COLLOIDAL MICROCRYSTALLINE CELLULOSE AS A SECONDARYRHEOLOGICAL ADDITIVE FOR WATERBORNE COATINGS1AYLING, G. ; YANG, S. ; LYNCH, G.FMC Corporation – Specialty Chemical Division – BioPolymer, Philadelphia, USA.1george.ayling@fmc.com; brasil.biopolymer@fmc.comKey-words: rheological agent, paint coating, microcrystalline cellulose, waterbornecoatings.SUMMARYColloidal microcrystalline cellulose (MCC) has been used widely in the food andpharmaceutical industries to suspend dense particles, prevent phase separation andstabilize emulsions. This study demonstrates that colloidal MCC has the samefunctionalities in waterborne coatings. It significantly improves the in-can shelf stabilityof waterborne coatings without negatively impacting application properties.INTRODUCTIONWaterborne coating systems are complicated. There are three basic ingredientsfound in typical coatings: pigments, polymers (also known as binders or resins) andsolvents. Each ingredient plays an important role in forming a durable and protectivefilm when the coating is dried.Pigment dispersion controls hiding, chalking, tint retention, color and sheenuniformity, flexibility, gloss, scrub resistance, color development, corrosion resistance,blistering, touch up and leveling of the coatings. Additives such as dispersants andrheology modifiers are added into the formulation to help disperse the pigments andstabilize the system through thickening and suspending.Rheology modifiers are important stabilizing agents in waterborne coatings.Although their use level is low, they control the flow of the liquid system and thus affectmany coating processes and performance. Rheology-controlled processes in coatingstechnology are stirring, mixing, pigment dispersion, pouring, pumping, coatingapplication, spreading, sagging, leveling, penetration into porous substrates, andpigment settling. Rheology modifiers also affect coating performance such as storagestability, color acceptance, film build, hiding powder, spatter resistance, scrubresistance, water resistance. Since all rheology modifiers thicken the system, and thethickening agent more or less modifies the rheology of the system, this paper uses bothterms interchangeably.Commercially available rheology modifiers can be divided into two categories:conventional and associative. A conventional rheology modifier thickens the waterphase of a coating due to hydrodynamic size (chain entanglement or gelling) andflocculative mechanisms. Examples of conventional thickeners are hydroxyethylcellulose (HEC), ethylhydroxyethyl cellulose (EHEC), hydroxypropylmethyl cellulose(HPMC), alkali-soluble or swellable emulsions (ASE), biopolymers, and inorganics,

such as clays. This class of thickening agents, in general, has the benefit of low costand convenience in use.Associative thickeners are water-soluble polymers with hydrophobic groups thatinteract non-specifically with other coating components to increase viscosity and modifythe rheology. They are normally chemically modified polymers, such as hydrophobicallymodified HEC (HMHEC) or EHEC (HMEHEC), hydrophobically modified ethoxylateurethanes (HEUR), and hydrophobically modified ASE (HASE).Each type of rheology modifier has its own performance attributes andlimitations. For example, modified celluloses such as HEC or HPMEC have been themajor products controlling the rheology behavior of acrylic latex paints. However, theynegatively affect coating properties such as leveling, spatter resistance and/or glossdevelopment. Hydrophobically modified cellulose (HMHEC) improves spatterresistance properties but has the limitation of biostability. HASE gives good glossdevelopment and easy handling, however, it imparts poor early water resistance and isnot alkali-resistant. HEUR overcomes these deficiencies and offers improved flow andleveling, film build, spatter resistance and good sprayability to the paint. The problem isthat they convey poor sag resistance, color incompatibility, viscosity drop on tinting anddilution as well as poor storage stability.This study addresses some of the deficiencies encountered here by usingcolloidal MCC as a stabilizer and secondary rheology modifier to further stabilize thesystem. Although the study examines only acrylic gloss paint formulations with HEURthickening agents as primary rheology modifiers, the application is suitable to otherwaterborne coating systems with other thickening agents.Colloidal MCCMicrocrystalline cellulose is produced by isolating and disintegrating thecrystalline regions of cellulose in an aqueous-based process (Figure 1). It isphysiologically inert, odorless and tasteless, making it suitable as a binding agent ordisintegrant in the tablet formulations (non-colloidal MCC).Figure 1 - Manufacturing process of MCC.

FMC’s patented technology co-processes MCC with various solublehydrocolloids like carboxylated methylcellulose (CMC), to keep the microcrystals fromreaggregating during the drying process. These co-processed MCC are referred to ascolloidal MCC because they can be dispersed in water. The hydrocolloids act as barrierdispersants to protect the cellulose from excessive hydrogen bonding during the dryingprocess, and also to aid in the re-dispersion (“activation”) of the dried MCC in theaqueous phase. The technology provides products with specific viscosity, suspensionand stabilizing properties, and thus makes them suitable for many industrialapplications.Colloidal MCC was used successfully in waterborne coating systems to stabilizethe formulation. It was found to be an excellent stabilizer and dispersing aid, due to itssuperior suspending functionality and emulsion stabilizing ability. The work describedhere summarizes some results in acrylic gloss paint systems.EXPERIMENT, MATERIALS AND RESULTSThe materials used in this study and their suppliers are listed in Table 1. Thereare several grades of colloidal MCC products available from FMC Corporation toprovide a wide functionality range with different activation requirements. The one usedin the study was Lattice NTC 80 (colloidal MCC) because it was found to be the mostsuitable for coating applications.Table 1 – Gloss Paint FormulationFunctionSupplier1. Pigment grind stageWaterLattice NTC80Ethylene glycolNeosept 95Orotan 731-KBykTM 025Ti-Pur R706Texanol BykTM 025Primal EP 2596Acrysol RM 2020Acrysol RM 8WStabilizerFMC BiopolymerMerckPreservativeISPDispersing agentRohm & HaasAntifoamByk-ChemiePigmentDuPont2. Letdown stageCialescing agenEastmanAntifoamByk-ChemieAcrylic latexRohm & Haas3. Rheology control stageHEUR thikenerRohm & HaasHEUR thikenerRohm & HaasTotal% .10100.008.901.301270.45COATING FORMULATIONSThe general coatings composition used in this study is also is also summarized inTable 1. The pigment dispersion was prepared with a Cowles-type mixer at high speeduntil Hegman 7.5 was achieved. ASTM method D 1210 was used to test the Hegmanfineness of the grind. Other ingredients were then added at low mixing speed.Evaluation methods are summarized in Table 2.

Table 2 - Evaluation Procedures - Industry standard methods usedParameterTest method detailsGlossD523, higher number indicated higher glossPigment grindD1210 (ASTM), higher number indicates finer particle sizeStormer viscosityD562, higher number indicates higher paint viscosity in the canD 4287, higher viscosity (at 12,000 s-1) indicates higher brush loading and better filmbuildICI viscosityFreeze/thaw stabilityD2243Spatter resistanceD4707 (ASTM), higher number indicates greater resistance to spatterSag resistanceD4400 (ASTM), higher number indicates greater resistance to sagLevellingD4062 (ASTM), higher number indicates better levellingHigh temp. stabilityD1849 (52ºC, 125ºF x 28 days)Commercial predispersions of tinting agents in propylene glycol were added at adosage of 2%TintingFUNCTIONAL PROPERTIES OF

Primal EP 2596 Acrylic latex Rohm & Haas 56.0 714.80 3. Rheology control stage Acrysol RM 2020 HEUR thikener Rohm & Haas 0.70 8.90 Acrysol RM 8W HEUR thikener Rohm & Haas 0.10 1.30 Total 100.00 1270.45 COATING FORMULATIONS The general coatings composition used in this study is also is also summarized in Table 1 .