A formulator shortlisting silicon dioxide for a body scrub, a toothpaste and a matting powder is not buying one material in three pack sizes. The three grades share a chemistry — synthetic amorphous silicon dioxide, CAS 7631-86-9 — and in some cases share parts of a compliance file, but they are specified against different physical properties and they fail in different ways. Treating them as one line item is one of the most common sourcing errors in this category.

The shortlist logic is straightforward once the functions are separated. For body scrub, particle size and morphology determine the exfoliation signal on skin. For toothpaste, the relative dentin abrasion (RDA) level combined with thickening behaviour must match the product positioning — daily care, sensitive or whitening. For matting powder, pore structure, a narrow particle size distribution (D50 2–9 µm across the ZLSIL-SG range) and a refractive index close to that of the resin (RI ≈ 1.45) decide both gloss and film clarity. Price comparison only becomes meaningful after those three functions are defined.

Why one chemistry produces three different materials

Industrial silicon dioxide is manufactured by one of three routes, and the route, not the formula, sets the performance envelope. Precipitated silica is produced from sodium silicate and acid in a wet process below 100 °C, then filtered, dried and milled or granulated; its primary particles aggregate into a porous structure that adsorbs liquids. Gel silica is produced with a deliberately controlled pore structure, which raises adsorption capacity. Fumed silica is made by flame hydrolysis of silicon tetrachloride above 1000 °C and delivers nanoscale primary particles at purity of 99.8% or higher.

That is why a scrub particle, an oral-care abrasive and a coating matte agent can all be labelled silica while sharing almost no performance characteristics. The scrub grade is designed to remain a discrete, perceptible particle that rinses away. The toothpaste grade is designed to abrade gently, disperse in a humectant and surfactant matrix, and build thixotropy so the paste does not separate. The matting grade is designed to sit at the film surface and scatter light in a controlled way.

The four reported parameters that carry most of the decision

A shortlist can be narrowed to a workable set of candidates using four values from the certificate of analysis and technical data sheet. None of them is a ranking on its own; each answers a different question.

D50 — the median particle size

D50 is the diameter at which half the particles by volume are finer. It is the first filter, because it maps directly onto user-perceived texture. Too coarse a particle produces grit or sediment; too fine a particle raises dusting, agglomeration and suspension problems. In oral care, high-cleaning abrasive grades are commonly specified around D50 10–14 µm, while the ZLSIL-SG matting series is designed at D50 2–9 µm with a deliberately narrow distribution, because a wide tail shows up as uneven gloss and surface roughness.

Oil absorption (DBP) — how much liquid the grade can carry

Oil absorption measures pore capacity to take up oils and liquids, expressed as millilitres of dibutyl phthalate per 100 g. A higher value means higher liquid loading capacity. This is the parameter that decides whether a grade can carry an emollient, a fragrance or a liquid active and still deliver a free-flowing powder, and it also correlates with how strongly a matting grade competes with the binder for solvent.

BET — the surface available for adsorption

BET specific surface area, measured by nitrogen adsorption, indicates how developed the porosity is. Two grades with identical D50 can behave very differently because one has substantially more internal surface. Where the job is adsorption rather than spacing, BET is the more predictive number; where the job is texture, D50 usually dominates.

pH — the compatibility filter

Standard precipitated grades sit at a near-neutral pH of roughly 6.5–6.8. Purpose-built acidic grades also exist — for example an acidic grade at pH 2.6 for acidic systems, and oil-refining grades at pH 1.5–3.0. pH only becomes visible as a problem when a sensitive ingredient degrades: vitamins, enzymes and some active ingredients are affected by a mismatch, and the failure appears weeks later in stability testing rather than on the line.

Body scrub: Hydrated Silica for Body Scrub

The ZLDIO-PC series — ZLDIO-PC9000, ZLDIO-PC2200, ZLDIO-PC250, ZLDIO-PC22 and ZLDIO-PC50 — is the cosmetic silica line, declared under the INCI name Silica. It is a naturally derived mineral under ISO 16128, which is why it has become a common answer to the formulation brief that asks for an exfoliant without a synthetic polymer bead.

In a scrub, the particle is the product. It must be perceptible on skin, must not collapse under shear in the tube, and must rinse cleanly. Because the series spans several grades rather than one, the shortlist question is not which silica but which point on the series matches the intended exfoliation intensity and after-feel — a judgement that is made on a sample, not on a data sheet.

What to verify on a scrub sample before committing:

• Whether the particle remains suspended through an accelerated storage period instead of settling into a hard layer at the bottom of the tube.
• Whether the exfoliation signal survives the surfactant system, since a high-foaming base changes how a particle is perceived.
• Whether the grade carries the odour and colour profile expected in a fragrance-heavy formula.
• Whether the finished product documentation names the material as Silica consistently across the INCI list, specification and label.

One structural difference from traditional scrub media is worth flagging early in development: silica does not dissolve. Salt and sugar scrub particles change the base during storage, so the viscosity and preservative system can be designed around a shrinking particle. A mineral particle is permanent, so the suspension system has to be designed for it from the start rather than corrected later.

Toothpaste: toothpaste grade silica

Hydrated Silica for Toothpaste is the most technically constrained of the three. In an oral-care paste, one excipient has to do two jobs at once: it is the abrasive that removes plaque and extrinsic stain, and it is the structuring agent that gives the paste its thixotropy — the ability to hold shape on the brush, extrude smoothly and resist water separation and stratification during shelf life. The ZLSIL-T range (ZLSIL-T116, ZLSIL-T113, ZLSIL-T101, ZLSIL-T120, ZLSIL-T124, ZLSIL-TY2, ZLSIL-T163, ZLSIL-T104, ZLSIL-T103) covers these different balances rather than a single universal grade.

The governing selection criterion is RDA. High-RDA abrasive grades are built for whitening and strong-cleaning pastes; medium-RDA grades serve general care; low-RDA grades are designed for sensitive teeth and children, where rounded particles clean without aggressive enamel wear. Thickening grades are a separate axis, offered in low, medium and high viscosity, with high-clarity variants for transparent gels. Toothpaste grades are commonly specified against QB/T 2346-2015.

Two quality attributes matter more in oral care than in most other applications. The first is iron. Ultra-low iron content prevents the black speck and paste discolouration problems that appear when trace iron meets certain flavour systems. The second is chemical inertness: silica does not react with fluoride, desensitising agents, herbal extracts or probiotic ingredients, which is what allows one grade family to serve fluoride, herbal, whitening and probiotic lines without reformulation conflicts. A three-year supply relationship in Korea, covering general-care, sensitive and functional toothpaste across a 100 T programme, illustrates how far a single qualified family can be stretched — but only after each variant has been trialled separately.

Where the boundary sits: a high-RDA whitening grade is the wrong choice for a sensitive-teeth product even though it fully complies with the same standard. The standard defines the category, not the positioning, and it will not tell you which RDA band your marketing claim requires.

Matting powder: a different regulatory universe

Silica Matting Powder belongs to coatings, not to personal care. The ZLSIL-SG range — ZLSIL-SG30, ZLSIL-SG40, ZLSIL-SG50, ZLSIL-SG60, ZLSIL-SG70, ZLSIL-SG90, the ZLSIL-PG thickeners and the coarser ZLSIL-SG400 to ZLSIL-SG700 sub-series — is a precipitated and gel porous silica matting agent with D50 2–9 µm, high oil absorption, narrow particle size distribution and RI ≈ 1.45. Applications are wood coatings, industrial and UV coatings, leather finishing and inks.

The performance brief is optical rather than tactile. A well-matched grade delivers:

• Adjustable gloss from high satin to full matte without speckling or whitening.
• Low interference with film clarity in clear varnish systems, so hardness, abrasion resistance and weather resistance are not sacrificed for the matte effect.
• Dispersion in solvent-borne, water-borne and UV-curable systems with low agglomeration, which shortens dispersion time and reduces energy consumption.
• Improved suspension and anti-sedimentation behaviour, preventing hard sediment at the tank bottom.
• Chemical inertness with acrylic, polyurethane, epoxy and polyester resins, plus improved scratch and mar resistance at the film surface.

The matting series is documented for coating, leather and ink use. It is not a food or oral-care ingredient, and food-contact status for a coated article must be confirmed against a separate food-contact grade rather than assumed from the word silica on the label. This is the single most common documentation mistake when a buyer consolidates all silica purchases into one request for quotation.

Where the shortlist breaks: real boundaries and trade-offs

A shortlist that does not state its limits is a sales document. Three boundaries deserve to be written into the evaluation plan from day one.

Certificate compliance is not performance compliance. A grade can meet every specification and still disappoint in a specific formulation, because in-spec parameters only mean the material is chemically compliant. Two grades with near-identical sheets can behave differently in the same base, and end performance is also governed by the formulation, the process and the equipment.

Matte and clarity pull against each other. A matting powder cannot deliver maximum film clarity and maximum gloss reduction at the same loading. Raising the loading lowers gloss and simultaneously raises viscosity and haze. The right loading is the lowest one that hits the gloss target, found by a gradient, not by the supplier data sheet.

Substitution against established mineral alternatives carries cost, not just chemistry. Calcium carbonate and dicalcium phosphate remain perfectly serviceable toothpaste abrasives; the difference is that abrasive and rheology functions then have to be delivered by separate ingredients, which adds a raw material to the formula and a supplier to the qualification file. Similarly, salt and sugar remain cheap scrub media where dissolution during storage is acceptable, and organic matting agents remain viable where a silica matte surface is not wanted. Silica wins where one excipient must carry two functions or where a mineral, non-dissolving particle is required — not automatically.

Pilot trials are not optional in any of the three applications

Because certificate compliance does not guarantee finished-product performance, pilot work is the point where a shortlist becomes a specification. A defensible pilot at 1–25 kg scale follows five steps.

1. Fix the benchmark parameters up front: D50, oil absorption, pH and loss on drying.
2. Run parallel tests at the same dosage as the incumbent formulation so the comparison is like for like.
3. Evaluate the attributes that the consumer or the customer actually perceives: flowability, anti-caking or matting performance, colour and solubility or dispersibility.
4. Run accelerated stability at 40 °C and 75% relative humidity for two to four weeks.
5. Document the results and authorise scale-up only where performance is acceptable.

Two disciplines make the result usable. Pilot material must come from the same batch that will be used for full-scale production, and trial samples must be sealed and retained. Skipping the pilot and moving straight to full production is the single most expensive shortcut in this category, because the failure mode — separation, haze, grittiness, discolouration — usually appears after filling, not during mixing.

What is changing in how buyers treat silica

Two shifts are visible in how industrial buyers now approach this material. The first is that silica is increasingly specified as a functional design parameter rather than a commodity filler: formulators ask for D50, oil absorption and pH before they ask for a price, because those three numbers decide whether the finished product passes its own stability test. The second is documentation-driven. Naturally derived mineral status under ISO 16128, plus the general move away from intentionally added microplastics in rinse-off cosmetics, has raised the value of an inorganic, non-bioaccumulating particle — silica released to the environment returns to the natural silicon cycle as sand and rock.

A third, quieter shift is portfolio consolidation. Buyers who previously sourced oral-care silica, cosmetic silica and coating matting agents from three different suppliers are now asking one supplier to demonstrate capability across all three, because a single qualification file is cheaper to maintain than three.

Outlook

The three applications will keep diverging rather than converging. Oral care is moving toward more precise RDA banding and more transparent formulations, which pushes demand for tighter particle size control and lower iron. Rinse-off personal care is moving toward mineral alternatives that survive a full shelf life without a preservation compromise. Coatings are moving toward UV-curable and water-borne systems, where dispersibility and suspension behaviour matter as much as gloss. What unites them is the requirement that the supplier can evidence the grade, not just name it — and that evidence is built in a pilot, not in a brochure.

Supplier context

Zhonglian Food Silica is the overseas-facing brand of Shandong Zhonglian Chemical Co., Ltd., a silicon dioxide producer within Zhongqi (Guangdong) Silicon Materials — a National High-Tech Enterprise listed on the Guangdong Equity Exchange in 2021 under code 880747 — supplying food-grade, oral-care, cosmetic and industrial silica from GMP-compliant workshops in China. The company reports annual silica capacity of approximately 50,000 metric tons, 45 patents across production, powder handling and packaging, and an in-house testing centre with a dedicated microbiological laboratory. Management systems are certified to ISO 9001:2015, ISO 22000:2018 and FSSC 22000 v6.0, with HALAL and OU Kosher certification on the product side. For procurement planning, standard grades are quoted at a 1 t minimum order with 7–10 day lead time, subject to product, quantity, inventory and destination.

The relevant point for this shortlist is portfolio breadth rather than a single hero grade: the same supplier documents ZLDIO-PC scrub grades, ZLSIL-T toothpaste grades and ZLSIL-SG matting powders, each against its own application basis, which is what makes a three-way comparison possible without three qualification projects.

FAQ

Why can one silicon dioxide grade not serve body scrub, toothpaste and matting powder?

Because the three applications depend on different physical properties of the same chemistry. A body scrub needs a discrete, perceptible particle that stays suspended in a surfactant base; toothpaste needs a particle that abrades within a defined RDA band while simultaneously building thixotropy in a humectant matrix; matting powder needs a porous particle with a narrow size distribution and a refractive index close to the resin so it scatters light without hazing the film. A grade optimised for one of these will be out of specification for the other two.

Which parameters belong on the comparison sheet first?

D50, oil absorption (DBP), BET specific surface area and pH. D50 governs perceived texture and settling; oil absorption governs how much liquid the grade can carry; BET indicates how developed the porosity is and therefore how much adsorption capacity exists; pH governs compatibility with sensitive ingredients. Refractive index is added as a fifth parameter only for coating applications, where it determines whether a matte clear film stays clear.

Why are pilot trials necessary before scale-up?

Because certificate of analysis compliance does not guarantee finished-product performance. In-spec parameters only confirm that the material is chemically compliant; end performance is also affected by the formulation, the process and the equipment, and two grades with similar specifications can perform very differently in the same base. A pilot at 1–25 kg scale, run against the incumbent at identical dosage with two to four weeks of accelerated stability at 40 °C and 75% relative humidity, is the minimum evidence required before committing to full-scale production.

Why does pH matter, and when is an acidic grade the right choice?

Standard precipitated grades are near-neutral at roughly pH 6.5–6.8, which suits most oral-care and personal-care systems. Purpose-built acidic grades exist — an acidic grade at pH 2.6 for acidic systems and oil-refining grades at pH 1.5–3.0 — and are selected when the surrounding formulation is itself acidic. A pH mismatch can degrade sensitive ingredients such as vitamins, enzymes and some active ingredients, and the effect typically surfaces during stability testing rather than during production, which is why a pH compatibility trial precedes any formulation based on a new grade.

What is the practical difference between precipitated, gel and fumed silica in these three applications?

Precipitated silica is made from sodium silicate and acid in a wet process and offers the best value for general anti-caking, flow and abrasive functions, which is why it underpins most oral-care and personal-care grades. Gel silica has a controlled pore structure and higher adsorption capacity, and is used where liquid loading dominates. Fumed silica is produced by flame hydrolysis, has nanoscale primary particles and purity of 99.8% or higher, and is typically chosen for thixotropy and high-clarity systems rather than for scrubbing or matting.

Do matting powder grades carry the same documentation as toothpaste grades?

No. The ZLSIL-SG matting series is documented for wood coatings, industrial and UV coatings, leather finishing and inks, and is supplied with COA, MSDS and application guidance for those uses. Toothpaste grades are specified against oral-care requirements including QB/T 2346-2015 and are supported by oral-care compliance documentation. Where a coated article must meet food-contact requirements, a separate food-contact grade should be specified rather than relying on the matting grade.

For formulators who want the full grade list, technical parameters and application notes in one document, the supplier publishes a downloadable food-grade silica brochure: Food Grade Silica Brochure (PDF).