CMC’s degree of substitution (DS 0.65–0.9) directly determines three performance parameters: 保水, 粘度, ，以及 solubility. DS counts the average number of hydroxyl groups on each anhydroglucose unit replaced by carboxymethyl (–CH₂COONa) groups. Each substituted group ionizes in water, creating a negatively charged polyelectrolyte chain that binds water through ion-dipole interactions and extends the chain through electrostatic repulsion.
水分滞留 rises with DS: more carboxylate groups immobilize water in hydration shells and form a denser gel network resisting evaporation and substrate suction. 粘度 increases with DS at equal molecular weight and concentration, because greater charge density extends the polymer coil and enlarges hydrodynamic volume. 可溶性 follows a threshold — DS ≥0.7 achieves rapid cold-water dissolution with ≤0.3% insoluble residue, while DS <0.7 leaves residual crystalline cellulose domains that hydrate slowly.
For construction mortar, DS 0.7–0.9 is optimal, balancing carboxylate density for water binding, chain extension for rheology, and cold-water solubility for on-site mixing. Below DS 0.65, water retention drops sharply and insoluble residue exceeds spec; above DS 0.9, cost premium yields diminishing returns while salt sensitivity rises in high-alkaline cement. Michem CMC spans DS 0.65–0.9 with customizable viscosity (400–8000 mPa·s), enabling formulators to match performance without over-specification.
DS selection is not an academic nuance — it determines whether CMC performs in the field or fails under job-site conditions. In dry-mix mortar, the difference between DS 0.65 and DS 0.85 can mean significantly higher water retention: full cement hydration versus surface crusting and strength loss.
Consider a tile adhesive applied in summer at 35°C on porous concrete. A low-DS CMC at 0.2% dosage may lose a large fraction of its mixing water within 15 minutes — insufficient for adequate hydration, risking adhesive failure. The same dosage of higher-DS CMC retains water longer, ensuring complete hydration and bond strength.
For procurement and formulation teams, understanding the DS-performance relationship eliminates trial-and-error in qualification. Specifying the correct DS range narrows selection to functionally equivalent products. Michem’s consistent DS control ensures lab-validated performance reproduces at scale — eliminating the most common cause of field performance drift in cellulose ether formulations.
CMC is produced by reacting alkali cellulose with sodium monochloroacetate (SMCA). Each glucose unit contains three reactive hydroxyl groups at the C2, C3, and C6 positions. DS counts the average number of hydroxyls replaced by carboxymethyl (–CH₂COONa) groups per anhydroglucose unit (theoretical max 3.0). In industrial-grade CMC, substitution is non-uniform — C6 primary hydroxyls react preferentially, followed by C2. The distribution affects performance independently of total DS: C6 substitution dominates solubility, while C2/C3 substitution influences chain stiffness and viscosity. DS titration testing per ASTM D1439 confirms the substitution level reported on each Michem product data sheet, providing a standardized, verifiable metric for qualification.
Each –CH₂COONa group dissociates in water to –CH₂COO⁻ + Na⁺, creating a negatively charged polyelectrolyte chain. Water binds to these anionic sites through ion-dipole interactions and hydrogen-bonding networks. At DS 0.8, a CMC chain of moderate DP carries hundreds of carboxylate groups, each immobilizing several water molecules — unavailable for evaporation, available for cement hydration.
The mechanism operates through two effects: bound water (immobilized in hydration shells) and network entrapment (CMC chains form a gel network that impedes water migration through capillary channels). In DS-optimization trials across mortar and ceramic applications, increasing DS from 0.65 to 0.85 at fixed dosage consistently reduced water-loss rate, confirming the DS–water-retention relationship under real conditions.
CMC in solution exists as an extended random coil due to intra-chain electrostatic repulsion between carboxylate groups. Higher charge density increases persistence length, enlarging hydrodynamic volume and raising viscosity at equal concentration and molecular weight. Viscosity measured per ASTM D2196 viscosity methods shows that, at fixed DP and concentration, viscosity rises with DS non-linearly and flattens above DS 0.85 as chain extension approaches maximum. The effect is amplified at low ionic strength and reduced in cement pore solution (high Ca²⁺, pH 12–13), where divalent ions screen electrostatic repulsion. Yet higher DS still resists complete chain collapse — a critical advantage in high-alkaline environments.
CMC solubility follows two steps: (1) water penetration into amorphous regions causing swelling, and (2) chain disentanglement and dissolution. Unsubstituted cellulose is water-insoluble due to inter-chain hydrogen bonding; each carboxymethyl group breaks several such bonds and introduces a hydrophilic, ionizable site. At DS <0.4, CMC is only alkali-soluble. At DS 0.4–0.65, partial cold-water solubility exists but dissolution is slow with insoluble residue. At DS ≥0.7, substitution density disrupts crystallinity, enabling complete cold-water dissolution within minutes — consistent with the ≤0.3% water-insoluble matter spec on Michem CMC. DS titration testing per ASTM D1439 confirms that batches meeting this threshold consistently report DS ≥0.7, validating it as a reliable specification boundary.
The following reflects Michem CMC product specifications (CAS 9004-32-4). Values are from Michem product data sheets; grade and process variations apply.
参数 | 规格 |
Product | |
CAS号. | 9004-32-4 |
Ionic type | 阴离子 |
取代度（DS） | 0.65–0.9 (customizable) |
纯净 | ≥99.5% |
氯化物 | ≤0.5% |
干燥损失 | ≤8.0% |
pH（1%溶液） | 6.5–8.5 |
水不溶性物质 | ≤0.3% |
Viscosity (1% solution, 25°C) | 400–8000 mPa·s (customizable) |
推荐用量（干混砂浆） | 0.1%–0.3% |
应用 | 食品、药品、化妆品、洗涤剂、陶瓷、油田、建筑 |
Source: Michem CMC Technical Data Sheet, michemicals.com/cellulose-ether/cmc. DS and viscosity are customizable within the stated ranges; confirm grade-specific values with Michem before specification.
Selecting DS balances water retention, rheology, and solubility against system chemistry (cement vs. gypsum), substrate absorbency, and ambient conditions:
Synergy with other ethers: CMC works synergistically with HPMC and HEMC. Lower-dosage Michem CMC (DS 0.8) with HPMC can outperform HPMC alone in water retention at lower total ether cost — CMC provides bulk water binding, HPMC contributes thermal gelation and air-entrainment stability.
Dosage adjustment: On high-absorption substrates (aerated concrete, clay brick), increase DS rather than dosage. Moving from DS 0.7 to 0.85 at the same dosage typically yields better water retention than increasing low-DS dosage, and avoids excessive viscosity.
Mixing protocol: Pre-blend CMC with cement or sand before adding water. Adding CMC directly to water causes lumping; pre-blending separates particles for uniform dispersion.
Temperature compensation: For hot-weather application (>30°C), specify a higher DS grade (0.85–0.9) and moderate dosage increase to preserve open time.
DS 0.9 provides higher water retention than DS 0.7 at equal dosage — longer open time and more complete hydration, valuable on porous substrates and at elevated temperatures. For interior wall tile on non-porous substrates, DS 0.7–0.75 is often adequate. Weigh the cost premium against the performance requirement.
Yes, but with optimization. Gypsum systems require lower DS (0.65–0.75) because gypsum has lower water demand and shorter setting time; excessive retention delays setting and reduces hardness. Cement systems benefit from higher DS (0.75–0.9) due to longer hydration and higher alkalinity.
DS is determined per ASTM D1439 DS determination methods, providing a standardized, reproducible measurement. Michem reports DS on each data sheet and controls production within tight tolerances so lab-validated performance reproduces at scale. Confirm grade-specific tolerances with Michem during specification.
No. Viscosity is primarily determined by cellulose degree of polymerization (chain length), while DS determines charge density, water retention, and solubility. Michem produces DS 0.85 CMC at viscosities from 400 to 8000 mPa·s, enabling independent selection of water retention (DS) and rheology (viscosity grade).
Insufficient DS manifests as: visible undissolved gel particles (insoluble residue), faster surface drying and skin formation, lower bond strength from incomplete hydration, and inconsistent viscosity between batches from variable dissolution kinetics. If these appear, verify DS ≥0.7 per ASTM D1439 and adjust upward in 0.05-unit increments until performance stabilizes.
This guide draws on two categories of evidence:
Michem product data: DS (0.65–0.9), purity (≥99.5%), chloride (≤0.5%), drying loss (≤8.0%), pH (6.5–8.5), water-insoluble matter (≤0.3%), viscosity (400–8000 mPa·s), and mortar dosage (0.1%–0.3%) are from Michem CMC Technical Data Sheets. Confirm grade-specific values with Michem before specification.
Recognized standards cited:
DS-performance relationships here are grade- and process-dependent; validate via lab testing for each formulation.
本指南适用于： Formulation engineers, procurement teams, and specifiers sourcing CMC for construction chemicals, ceramics, oil-field, and related applications. Assumes basic familiarity with cellulose ethers.
制作过程： Compiled by the Michem Technical Applications Team from product specifications, ASTM test methods, and field experience in mortar and ceramic applications. Product data is from Michem CMC Technical Data Sheets; references are from ASTM and ISO standards in References.
限制： The DS-performance relationship is grade- and process-dependent. DS values, viscosity grades, and dosages interact with formulation chemistry, substrate, and ambient conditions. Always validate selection via lab testing under target conditions before full-scale specification.
更新政策： Reviewed periodically as specifications and standards evolve. The “Last reviewed” date in the Editorial & Trust Box indicates the most recent review. For latest data, consult the current Michem CMC Technical Data Sheet.
Degree of substitution is the primary structural parameter governing CMC performance. DS 0.7–0.9 is the practical sweet spot for construction and industrial applications, balancing water retention, solubility, and cost. Within this range, each DS increment delivers measurable changes in water binding, viscosity, and dissolution — enabling formulators to match performance to requirements precisely.
Michem CMC combines DS 0.65–0.9, high purity (≥99.5%), low insoluble matter (≤0.3%), and customizable viscosity (400–8000 mPa·s) for reliable performance across dry-mix mortar, tile adhesive, wall putty, ceramic, and oil-field applications.
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