PVC Resin HS-800(SG-7)

PVC Resin HS-800(SG-7) is a low-K-value suspension homopolymer produced by suspension polymerisation of vinyl chloride monomer. The grade designation combines the supplier identifier HS-800 with the Chinese national resin classification SG-7, placing the material in the lower molecular mass segment of commercial rigid PVC. Typical certificates of analysis report a K-value of 57.0–58.5 determined according to ISO 1628-2:2022, with an average degree of polymerisation controlled at 780–850. The resin is supplied as a white powder with an apparent bulk density normally between 0.46 g/cm³ and 0.54 g/cm³. Compared with SG-5 grades having K-values of 66–68 and polymerisation degrees of 1000–1100, HS-800 exhibits lower melt viscosity, faster gelation, and improved flow in thin-wall moulds. The lower molecular mass also reduces tensile yield strength and notched impact resistance in unmodified rigid compounds, which limits its use in high-pressure fittings unless formulation adjustments are made.

Raw Resin Specifications and Batch-Release Limits Under GB/T 5761-2006

The SG-7 classification anchors HS-800 to the suspension resin acceptance framework of GB/T 5761-2006. Batch-release testing typically covers K-value, apparent bulk density, volatile content, residual vinyl chloride monomer, sieve residue, and whiteness. K-value is measured by dilute solution viscometry as specified in ISO 1628-2:2022. Apparent bulk density is controlled within 0.45–0.54 g/cm³ using the bulk density method. Volatile matter including moisture is limited to ≤0.30 wt%. Residual VCM determined by gas chromatography according to ISO 6401:2022 is typically below 1 µg/g, while the general-purpose limit in GB/T 5761-2006 is ≤5 µg/g. Sieve retention on a 0.25 mm screen is normally below 0.5%, and the mean particle diameter falls between 150 µm and 180 µm by laser diffraction. These powder properties influence gravimetric feeding accuracy, dry-blend absorption, and dust extraction load in compounding plants.

The bulk density and sieve data explain why HS-800 transfers easily through dense-phase pneumatic conveying but still requires dust removal for fines below 50 µm, which are typically present at 3–6% by volume. These fines can accumulate on vacuum pump filters and lead to feed pulsation if not managed with cyclone separation and baghouse units.

How Does the Lower K-Value Modify Fusion Behaviour and Melt Pressure in Counter-Rotating Twin-Screw Extrusion?

In dry-blend extrusion on a 65 mm parallel counter-rotating twin-screw line with an L/D ratio of 36:1 and barrel temperatures between 155 °C and 178 °C, HS-800 compounds typically complete fusion at 2–4 °C lower than SG-5 equivalents at equal stabiliser loading. The reduced molecular mass lowers peak fusion torque and steady-state melt pressure by approximately 5–12% when screw speed is held at 28–32 rpm. This permits either a lower barrel-temperature profile or higher throughput without exceeding drive current limits. Capillary rheometry at 190 °C and 100 s⁻¹ shows an apparent melt viscosity of 8.5 × 10³ to 1.2 × 10⁴ Pa·s for a rigid compound containing 4.0 phr tin stabiliser and 1.2 phr lubricant, whereas SG-5 formulations of the same additive loading fall within 1.5 × 10⁴ to 2.2 × 10⁴ Pa·s. The narrower molecular-weight envelope of the low-K suspension resin also reduces plate-out on vacuum-vented barrels, although this effect depends on lubricant composition and screw temperature control.

In thin-wall injection moulding of PVC pipe fittings, HS-800 (SG-7) is processed at melt temperatures of 190–200 °C and mould temperatures of 30–45 °C. The lower K-value increases spiral flow length by approximately 15–25% relative to SG-5 at the same injection pressure of 120–150 MPa on a 250-tonne clamping-force machine. This flow improvement supports filling of wall sections below 2.5 mm without raising melt temperature toward the degradation threshold. However, the same molecular mass reduction lowers tensile yield strength to 46–50 MPa when tested under ISO 527-2, compared with 52–55 MPa for SG-5-based rigid compounds. Notched Charpy impact strength under ISO 179-1/1eA is reduced by 2–4 kJ/m² in unmodified formulations. Published data for this specific tool configuration is limited, so the exact spiral-flow gain must be confirmed by short-shot trials on the production mould. HS-800 is therefore not a direct drop-in replacement for pressure-bearing fittings where long-term hydrostatic strength under ISO 9080 is the controlling requirement; the reduced molecular mass shifts the ductile-to-brittle transition and lowers design margin under sustained internal pressure.

When HS-800 Replaces SG-5 in Calendering of Transparent Rigid Film

Calendering trials with HS-800 require final-roll temperatures of 175–185 °C, compared with 180–190 °C for SG-5 recipes. The lower melt viscosity shortens residence time and reduces yellowing-index increase caused by thermal history. Film produced at 0.25 mm thickness typically exhibits light transmittance of 90–92% and haze below 2.0% when measured with ASTM D1003. Gel counts measured with an optical particle analyser remain below 5 per 100 cm² in laboratory sheets. The resin’s lower plasticizer absorption means that dry-blending time should be extended by 10–15% or the mixer temperature should be raised to 105–110 °C to avoid dry spots when 2–3 phr of internal lubricant is used. Because suspension PVC powder picks up surface moisture above 60% relative humidity, predrying at 70 °C for 2–3 hours is required before processing to prevent surface defects and bubble formation in calendered sheet.

Residual VCM, Heavy Metal Restrictions and Food Contact Documentation

For food-contact and toy-safety applications, HS-800 (SG-7) must be accompanied by batch documentation stating residual VCM and extractable heavy-metal content. Modern suspension production achieves residual VCM below 1 µg/g and often below 0.5 µg/g, satisfying the EU 10/2011 specific migration limit for VCM of 0.01 mg/kg in the final article when processing includes adequate degassing. The resin can be used in rigid PVC food-packaging formulations that comply with FDA 21 CFR 177.195, provided the finished compound is formulated with approved stabilisers and lubricants. REACH and RoHS compliance must be verified on the compound rather than the raw resin alone. Lead-based stabilisers are incompatible with RoHS-compliant product lines and should not be used in HS-800 formulations. Supplier documentation should include the ISO 9001 certificate and a batch-specific test report for residual VCM, because resin grade alone does not establish food-contact status.

Plasticizer absorption for HS-800 is measured in the range of 16–22 g DOP per 100 g resin under GB/T 3400, lower than 20–27 g/100 g for SG-5 and slightly higher than SG-8. This intermediate absorption level reduces the time needed to produce free-flowing dry blends in high-speed mixers, but liquid plasticisers should be introduced at 70–80 °C and mixed for an additional 8–10 minutes to achieve uniform adsorption. In flexible PVC formulations, the lower molecular mass of HS-800 reduces compound viscosity, allowing a 10–15% reduction in plasticiser level to reach the same Shore A hardness as SG-5-based compounds at equal filler loading. The lower molecular mass also increases plasticiser migration potential in long-term service, so permanent plasticisers of higher molecular weight or polymeric types are preferred when extraction resistance is specified under ASTM D1239.