GOHSENX T-350 is a partially saponified polyvinyl alcohol (PVOH) powder supplied as a suspension dispersant for vinyl chloride monomer (VCM) polymerisation. The grade carries a nominal degree of polymerisation of 350 and a degree of hydrolysis in the partially saponified range, which places it between low-viscosity surfactant-like PVOH grades and higher-molecular-weight film-forming grades. The product is dissolved in demineralised water before reactor charging; it is not formulated for film or adhesive end-use applications where bulk PVOH mechanical properties are required. Its primary function is interfacial: it adsorbs at the VCM/water interface under agitation, retarding droplet coalescence and controlling PVC grain morphology during the particle-identity period of suspension polymerisation.

The material is hygroscopic, and incoming quality control limits for volatile content are therefore used to correct gravimetric charging accuracy. The powder is combustible only as a fine dust cloud, and the aqueous solution is non-corrosive to stainless steel. These properties are standard for partially saponified PVOH; they do not differentiate T-350 from adjacent grades in the same series, but they define the storage and handling envelope of the product.

What Specification Boundaries Apply to GOHSENX T-350?

Compliance testing for the product is normally performed under JIS K6726, the Japanese Industrial Standard method for polyvinyl alcohol. The viscosity value refers to a 4% aqueous solution at 20 °C; the degree of hydrolysis is determined by saponification back-titration and is expressed as mol%. The following table consolidates the property limits reported in supplier technical documentation.

Lot-to-lot variation within these windows is normally below the threshold that would require reactor parameter adjustment. However, a batch near the upper degree-of-hydrolysis boundary can display slightly higher water solubility and lower VCM/water interfacial activity, while a batch near the lower boundary can produce a more surface-active but less water-soluble dispersant. In plants that operate within a narrow suspension window, this variation is compensated by adjusting the dispersant feed by a small trim amount rather than by altering the agitator curve.

In production-scale suspension PVC, the prepared GOHSENX T-350 solution is charged into the aqueous phase before VCM addition. The reactor is typically a jacketed stainless steel vessel with top-entering agitation and one or more baffles. The dispersant solution is introduced through a dedicated dosing line and passed through a 100 µm screen; retained gel aggregates are an early indicator of incomplete cold-water dissolution. The dispersant is typically evaluated at addition levels between 0.02 and 0.15 wt% based on VCM mass, although published data for the optimum T-350 concentration in a specific reactor configuration is limited. Agitation is set to maintain a stable monomer dispersion. Insufficient dispersant feed produces coarse grains and can lead to wall fouling, while overdosing raises continuous-phase viscosity, reduces heat transfer at the jacket, and can depress plasticizer absorption by the finished resin.

The dissolution step itself is a processing bottleneck on some lines. Cold water below 15 °C delays hydration of the PVOH particle surface and can leave undissolved fines; water above 40 °C can form a hydrated skin on the powder surface during addition, producing lump formation. The recommended dissolution window is therefore 20–30 °C with high-shear dispersion or recirculation through a static mixer. A typical preparation skid uses a stainless steel tank with a cowles-type disperser and a transfer pump delivering the solution through a 100 µm basket strainer. The solution is used before significant microbial growth occurs; holding times beyond 24 h at ambient temperature are not recommended unless a validated biocide is used.

The dispersant feed is normally checked against the torque curve of the reactor agitator. In batches where the primary dispersant concentration is too low, the torque signal during the early polymerisation stage may show a lower apparent viscosity because droplets coalesce and the interfacial area falls; however, the resulting grain size distribution becomes broader and the fines content below 63 µm increases. In batches where the concentration is too high, the torque signal remains elevated, the monomer dispersion is over-stabilised, and the median particle size becomes too fine for some rigid PVC applications. The practical control window is therefore defined by the combination of agitator torque, jacket heat-transfer coefficient, and final resin particle size, not by a single dispersant concentration.

In many suspension PVC recipes, T-350 is used with a secondary dispersant or a lower-DP PVOH grade to create a bimodal or broad particle size distribution. The primary dispersant controls the initial droplet size and the secondary dispersant modifies coalescence behaviour during the particle-identity stage. The ratio of primary to secondary dispersant is more important than the absolute amount of T-350. Published data for the optimum ratio in a specific PVC grade is limited; the ratio is typically developed through reactor trials because it depends on agitator type, baffle clearance, and monomer purity.

When GOHSENX T-350 Replaces T-330H or T-450 in Vinyl Chloride Suspension Polymerisation

The distinguishing variable between partially saponified GOHSENX T-series grades is nominal degree of polymerisation. At equal reactor temperature, agitator speed, and monomer-to-water ratio, substitution of a lower-DP grade such as the T-330H class by T-350 shifts the droplet size distribution toward a larger median diameter and lowers the fine fraction below 63 µm when measured by laser diffraction according to ISO 13320. The same substitution generally increases the protective film strength around the monomer droplet, which reduces coalescence during the particle-identity period. Conversely, replacing a higher-DP grade such as the T-450 class with T-350 reduces solution viscosity and can allow a higher monomer-to-water ratio without exceeding the agitator torque limit of the reactor drive. The selection depends on reactor geometry and target resin morphology rather than on any absolute product superiority.

The table is directional, not a substitute for reactor trials. On a 30 m³ reactor with a top-entering turbine, moving from the lower-DP grade to T-350 may require a 5–10% reduction in target dispersant feed if the median diameter is held constant. Moving from the higher-DP grade to T-350 may permit a 2–5% increase in monomer-to-water ratio at the same agitator torque, but published data for this specific configuration is limited. The actual adjustment depends on impeller diameter, tip speed, baffle clearance, and the presence of secondary dispersants.

The PVC resin produced with T-350 is evaluated by standard resin tests. Plasticizer absorption is measured according to ISO 4608; apparent bulk density according to ISO 60; and residual VCM content according to ISO 6401. The target values of these properties are set by the converter, not by the dispersant alone. A shift from T-330H to T-350 at constant addition level can raise plasticizer absorption slightly and reduce apparent bulk density; a shift from T-450 to T-350 can improve powder flow and reduce dry-blend mixing torque because the coarser grain morphology from the higher-DP grade is partially reversed. These differences are observed on production dry-blend lines equipped with torque-control mixers, and they are quantified by the converter rather than by the resin producer alone.

The residual acetyl content of the partially saponified PVOH also plays a role in final resin quality. T-350 typically retains a degree of hydrolysis between 72 and 75 mol%. Within this range, the hydrophile-lipophile balance is compatible with the VCM/water interface at polymerisation temperatures of 55–65 °C. If the degree of hydrolysis drifts upward, the dispersant becomes more water-soluble and less interfacial; the droplet stabilisation effect weakens, and the reactor may require a higher dispersant addition to maintain the same particle size. If the degree of hydrolysis drifts downward, the dispersant becomes more surface-active but less soluble, and dissolution-related defects can increase. This is why the specification window is relatively narrow and why the hydrolysis value is monitored in every incoming lot.

During polymerisation, the reactor pressure is maintained at the vapour pressure of VCM at the chosen temperature, typically 0.9–1.2 MPa absolute at 55–65 °C. The dispersant’s main effect is confined to the early conversion range before the PVC phase becomes rigid; after the particle identity point, agitation continues to suspend the growing particles, but the interfacial demand for the dispersant decreases. The batch is normally terminated after a pressure drop corresponding to a residual VCM content that is subsequently removed by stripping. The exact conversion at termination is determined by the resin producer’s target for residual monomer and grain porosity, not by the dispersant grade.

Wall fouling associated with dispersant failure is detected as a decline in the overall heat-transfer coefficient of the reactor jacket. Production experience indicates that fouling deposits containing PVOH, PVC fines, and monomer-swollen gel tend to accumulate first at the gas-liquid interface zone and behind baffles. The deposits are removed by high-pressure water jetting between batches; if the fouling is not removed, batch cycle time increases because the jacket cannot remove the heat of polymerisation at the designed rate. T-350’s contribution to fouling is primarily through undissolved powder or through a primary dispersant concentration that is too low to stabilise the monomer droplets. Both failure modes are prevented by dissolution filtration and by feed-rate control rather than by changing the grade alone.

Compared with hydroxypropyl methylcellulose (HPMC) used as a secondary dispersant, T-350 has a lower aqueous viscosity at equivalent concentration and does not undergo thermal gelation in the normal PVC polymerisation temperature range of 55–65 °C. Compared with gelatine-based suspension systems, T-350 shows less susceptibility to biological degradation in prepared solution, but microbial growth must still be controlled by hold-time limits or a validated biocide. Published data for ternary HPMC/gelatine/PVOH blends in T-350-based recipes is limited; plant trials generally retain the PVOH as the primary interfacial stabiliser and use HPMC only as a secondary particle-size modifier.

Unopened bags of T-350 should be stored in a dry area at 25 °C and relative humidity below 60%. Opened bags should be re-sealed and consumed within a limited campaign; moisture absorbed above 5.0% volatile content changes the net powder weight and can make dissolution more difficult. The powder is incompatible with strongly alkaline additives that accelerate hydrolysis of the residual acetate groups and with borate salts that can form diol complexes and raise solution viscosity. When pre-drying is required at relative humidity above 60%, the material should be dried with ambient dehumidified air below 40 °C to avoid particle fusion.