PVC Resin HS-1300(SG-3)

PVC Resin HS-1300 (SG-3) is a suspension-polymerised poly(vinyl chloride) homopolymer classified as grade SG-3 under GB/T 5761. The resin exhibits a K-value of 71–72 and an average degree of polymerisation of 1300–1350 when determined by dilute-solution viscometry according to ISO 1628-2. These chain-length parameters place the material in the medium-high molecular weight segment of the suspension PVC range, above SG-5 and below SG-2 in the Chinese grade sequence. The product is supplied as a free-flowing white powder with a typical apparent bulk density of 0.45–0.52 g/cm³ by ISO 60. The principal difference from SG-5 and SG-7 is the higher melt viscosity and melt strength derived from the 1300-level chain length, which supports flexible calender stock, cable insulation, and high-elongation semi-rigid profiles, but reduces maximum screw speed and output when the resin is used in rigid pipe extrusion without reformulation.

The K-value of 71–72 corresponds to a viscosity-average molecular weight at the upper end of the suspension PVC range typically used for flexible applications. Higher molecular weight increases melt viscosity and elastic recovery, which benefits die swell and size stability in profile extrusion but increases screw torque. K-value is used as a specification parameter rather than as a direct melt-flow indicator, because the relationship between K-value and molecular weight depends on the solvent system and Mark–Houwink constants employed.

When HS-1300 (SG-3) Is Evaluated Against GB/T 5761 and ISO 1628-2

The classification falls within the suspension PVC specification framework in which the SG-3 designation corresponds to a K-value band of 71–72 and a nominal polymerisation degree of 1300. Typical batch-release values are listed below.

A volatile-matter limit of 0.30 % by ISO 1269 is not only a shipping characteristic; it also determines extrusion surface quality. Resin stored at relative humidity above 60 % absorbs surface moisture that can form steam during gelation and lead to pinholes in film or rough surfaces in cable insulation. Pre-drying in a hopper dryer at 60–70 °C for 1–2 h is therefore applied before processing when storage conditions exceed that threshold. The apparent bulk density range of 0.45–0.52 g/cm³ permits consistent gravimetric metering from silo and hopper systems, but pneumatic conveying can generate fines when bend radii are below the supplier-recommended minimum. The suspension process produces grains with sufficient internal porosity to absorb liquid plasticiser, while the drying step preserves free-flowing behaviour. Published data for batch-to-batch variation on specific high-speed mixing configurations is limited.

What Limits the Substitution of SG-3 for SG-5 in Rigid Pipe Extrusion?

The SG-3 grade is not a direct substitute for SG-5 in high-output rigid pipe extrusion. SG-5 resins have K-value 66–68 and average degree of polymerisation 1000–1100, giving lower melt viscosity, faster gelation in counter-rotating twin-screw extruders, and less shear heating at constant screw speed. When HS-1300 (SG-3) is processed in a twin-screw extruder with an L/D ratio of 25:1–36:1, the die melt temperature rises relative to SG-5 at the same screw speed, reducing the thermal stabiliser margin. A rigid formulation developed for SG-5 must be rebalanced with external lubricant and stabiliser; otherwise the longer chain increases torque and reduces line speed before surface quality is affected.

In flexible applications, the same molecular weight difference is a processing advantage for retention of plasticiser. The higher chain length reduces plasticiser migration under stress and lowers equilibrium extraction loss in dry-blend and plastisol compounds when tested under ISO 177:2016. The substitution should nevertheless be validated with the specific plasticiser package, because plasticiser molecular weight and polarity often control the migration rate more than K-value alone. Compared with SG-7, HS-1300 (SG-3) also shows lower melt flow and is not recommended for thin-wall injection moulding where high flow length at low viscosity is required.

Suspension PVC grains of HS-1300 (SG-3) are composed of agglomerated primary particles with internal pores that control plasticiser absorption. The polymerisation temperature is inversely related to molecular weight, so the lower reactor temperature used for SG-3 yields the higher K-value relative to SG-5 and SG-7. The grain size distribution is designed to balance plasticiser uptake against apparent bulk density; excessive grain porosity increases plasticiser absorption but reduces bulk density and can create dusting during powder handling. The resin is supplied without heat stabilisers, lubricants, or processing aids, and therefore all melt-processing formulations require a stabiliser package before extrusion, calendering, or injection moulding.

HS-1300 (SG-3) is a homopolymer and is not directly comparable with vinyl chloride–vinyl acetate copolymers or chlorinated PVC. In rigid applications, chlorinated PVC has a higher heat distortion temperature, while the homopolymer retains easier plasticiser absorption and is supplied as a general-purpose suspension resin. In laboratory viscosity checks, the resin is dissolved in cyclohexanone at 25 °C according to ISO 1628-2; dissolution requires controlled agitation because the grain skins can resist rapid solvent penetration.

Plasticiser Absorption, Dry-Blend Dwell Time, and High-Speed Mixer Behaviour

High-speed mixing of HS-1300 (SG-3) in hot-cold mixer combinations prepares dry blends for cable, film, artificial leather, and injection moulding. The resin is charged into a high-speed mixer and heated to 105–120 °C while plasticiser is absorbed into the porous grain structure. After discharge, the blend is cooled in a horizontal cooling mixer to below 40 °C before storage to prevent blocking. The plasticiser absorption of the 1300-level grain is higher than that of SG-7, allowing plasticiser loadings above 45 phr without preheating the liquid phase, although the exact absorption endpoint depends on the suspending agent system and residual grain porosity. Mixing above the recommended discharge temperature can prematurely densify the grains and reduce plasticiser uptake in the next batch.

Incoming quality control should include sieve residue, volatile matter, and K-value on each lot. For flexible compounds, the plasticiser absorption test on the resin is used as a predictor of dry-up time in the hot mixer. A resin lot with plasticiser absorption below the control range will produce dry blends with longer maturation and can leave unplasticised grains in calendered film.

In wire and cable insulation, HS-1300 (SG-3) is processed on a single-screw extruder with a barrel L/D of 25:1–30:1 and a compression ratio of 2.5:1–3.5:1. The melt temperature is generally controlled between 160 °C and 175 °C for lead-free stabiliser systems. The higher molecular weight reduces sagging in thin-wall constructions below 0.5 mm and contributes to concentricity retention at the crosshead. Heat ageing is verified under IEC 60811-401 or an equivalent end-use standard, because plasticiser loss and elongation retention depend on the entire formulation, not on the resin K-value alone. The processing boundary is lower output at equivalent screw speed compared with SG-5; line speed must be established on the specific crosshead and screw design because the resin shear-heats more readily than lower-K-value grades.

Calendered flexible film and sheet operations use HS-1300 (SG-3) at roll temperatures between 165 °C and 185 °C on three-roll or four-roll calenders. The polymer exhibits a later fusion onset than SG-5 at the same roll temperature, so the bank residence time and roll gap are adjusted to prevent cold grain and pinhole defects. Once fused, the higher molecular weight results in higher tear resistance and lower surface blocking in thin-gauge flexible film. Tensile properties are tested under ISO 527-3 and tear resistance under ISO 6383-2; the values are formulation-specific, and no single tensile or elongation figure is representative of all SG-3 compounds. Calendering line speed is limited by gelation rate and the thermal stability of the stabiliser package, not by the feed capacity of the resin.

In compact and foam layers for artificial leather, HS-1300 (SG-3) is dispersed with plasticisers, fillers, and foaming agents in a high-shear mixing step and then coated or calendered onto release paper. The 1300-level degree of polymerisation permits foam formulations with 60–80 phr plasticiser to retain cell structure during the foaming stage and to resist exudation at ambient storage when the compound contains an epoxidised soybean oil costabiliser. The resin is not flame-retardant by itself; flammability classification must be achieved by the additive package under ISO 3795 or the applicable end-use standard. Production experience shows that the higher plasticiser demand of SG-3 requires longer dry-blend maturation than SG-5, and batch-to-batch variation in plasticiser absorption can be observed when the suspending agent system changes.

Flexible tubing, hoses, and gaskets based on HS-1300 (SG-3) are processed on single-screw extruders with a cooled screw and compression ratios between 2.5:1 and 3.5:1. The higher molecular weight yields higher burst-strength retention and kink resistance in thin-wall tubing than SG-7, but the compound requires a higher barrel temperature or a lower screw speed to reach full gelation. Compression-set behaviour is controlled by the plasticiser and cross-linking or high-molecular-weight plasticiser system rather than by the PVC K-value alone. Therefore comparative evaluation against SG-5 or SG-7 should be based on finished-part performance standards rather than on resin properties in isolation.

The resin is thermally processed only after the addition of an effective heat stabiliser. Dehydrochlorination is accelerated above 190 °C, and unprotected melt residence at temperatures above that threshold leads to discolouration and surface defects. The resin should be stored away from direct sunlight, strong oxidising agents, and moisture ingress. In high-shear mixing, frictional heating can generate local temperatures above the set point, so discharge temperature is monitored rather than total mixing time alone. These limitations are common to suspension PVC homopolymers and are not unique to HS-1300 (SG-3).

When mineral fillers are incorporated, the high melt viscosity of HS-1300 (SG-3) increases the dispersion energy required in the gelation stage. Calcium carbonate loadings of 20–40 phr are typical in flexible cable and artificial leather formulations. The use of stearic acid-coated fillers with a median particle size of 1–2 μm is associated with lower screen-pack pressure and can increase the external lubricant requirement while lowering the thermal stability margin slightly. The selection of filler type and loading is therefore made in conjunction with the stabiliser-lubricant package rather than by reference to the resin specification alone.

For regulatory declarations, HS-1300 (SG-3) homopolymer resin is supplied with batch certificates covering the relevant national chemical-control requirements. In food-contact end uses, the finished compound and article must comply with the applicable positive-list scheme, such as Regulation (EU) No 10/2011 or GB 4806.6-2016, because compliance is determined by residual vinyl chloride monomer content and by the additives rather than by the K-value grade alone. Residual vinyl chloride monomer for food-contact grades is typically controlled to below 1 mg/kg. RoHS compliance is assessed on the formulated article; the resin itself does not normally contain restricted phthalates, lead, cadmium, or hexavalent chromium unless introduced by downstream additives. Processors should verify the batch-specific certificate and regulatory declaration for the target jurisdiction before qualification.