Zhejiang Weitai Chemical Co., Ltd.

Zhejiang Weitai Chemical Co., Ltd. supplies chlorinated polyolefin and chlorosulfonated polyolefin resins for rigid PVC impact modification, high-temperature chlorinated PVC compounding, and metal-oxide- or peroxide-cured elastomer systems. The grade slate comprises chlorinated polyethylene (CPE) powders with chlorine content between 30 wt% and 37 wt%, chlorinated polyvinyl chloride (CPVC) resins with chlorine content between 66 wt% and 69 wt%, and chlorosulfonated polyethylene (CSM) grades containing chlorine 35–43 wt% and sulfur 1.0–1.5 wt%. Lot-release analytical protocols include ASTM D1646-19a for Mooney viscosity, ASTM D412-16 for tensile properties of cured CSM sheets, ASTM D2240-15 for durometer hardness, ASTM D792-20 for density, and ASTM D3030 for volatile content. Chlorine content is determined by oxygen-flask combustion followed by ion chromatography; no single ISO method is uniformly designated across all producer certificates. The CPE resins are produced by aqueous-suspension chlorination of high-density polyethylene; CPVC is produced by post-chlorination of suspension PVC; CSM is produced by chlorosulfonation in solvent. This route separation creates measurable differences in residual chlorocarbon carryover and cure behaviour relative to solvent-process CPE from other suppliers.

For the aqueous-suspension CPE process, hydrochloric acid is used as the chlorinating reactant and hydrogen peroxide as catalyst; residual acid is neutralized, leaving ash content below 0.50 wt%. In solvent-process CPE, the residual solvent content is a differentiating parameter. The aqueous route therefore supports lower residual volatile organic compound profiles in end-use articles, although published data for this specific configuration is limited.

Why Does Residual Crystallinity in CPE 135A Dictate the Impact-Modification Window in Rigid PVC?

Residual crystallinity in the CPE 135A grade, observed by differential scanning calorimetry at 10 K/min under nitrogen, appears as a melting endotherm between 55°C and 75°C. That endotherm controls the temperature at which the modifier transitions from discrete elastomer domains to a coalesced low-modulus phase during PVC fusion. In rigid PVC twin-screw extrusion on lines with 25:1 L/D and barrel zones set at 170–185°C, the 135A grade is fed at 8–12 phr. Below 8 phr, notched Izod impact measured by ISO 180 remains below 10 kJ/m² in unfilled PVC profiles; above 12 phr, the flexural modulus measured by ISO 178 commonly falls below 2100 MPa in formulations without mineral filler. The grade is specified at 35 ± 1 wt% chlorine and Mooney viscosity ML 1+4 at 125°C between 80 and 105, a range that balances impact efficiency and fusion torque. Aqueous-suspension chlorination provides a less blocky chlorine distribution than solvent-phase CPE, reducing residual crystallinity and accelerating fusion. Moisture content above 0.30 wt% causes feeding instability in gravimetric dosing units; incoming material is therefore pre-dried at 70°C for 2 h when storage humidity exceeds 60% RH.

Because aqueous-suspension chlorination lowers residual chlorocarbon carryover relative to solvent-process CPE, CPE grades from Zhejiang Weitai Chemical Co., Ltd. typically produce lower odour and lower extractable content in finished PVC articles, although published data for this specific configuration is limited. The 130A grade, with chlorine content near 30 wt%, has a lower glass transition and is used where cold-temperature impact is required. The 135B grade, with Mooney viscosity 55–70, is selected for injection-moulded PVC fittings where filling pressure limits require reduced melt viscosity. Compared with MBS and acrylic impact modifiers, CPE does not provide transparency and requires higher loading for equivalent room-temperature impact; however CPE-modified PVC retains impact resistance after 3000 h of QUV-B exposure to ISO 4892-3 with ΔE shift below 5 in some mineral-free exterior grade formulations. Compared with acrylic modifiers, CPE at 8 phr generally provides lower notched impact at -30°C but better resistance to environmental stress cracking in contact with zinc chloride solutions. Production-scale twin-screw compounding has recorded barrel temperature reduction of 5–8°C when switching from a higher-crystallinity solvent-process CPE to an aqueous-suspension grade, due to earlier dispersion and lower melt viscosity after fusion.

CPVC Resin Thermal Stability Limits and the Role of Chlorine Distribution in Pipe Extrusion

CPVC resins are applied in rigid piping and sheet where heat deflection temperature measured by ASTM D648 exceeds 100°C at 0.455 MPa in stabilised compounds. The resins are differentiated from commodity PVC by chlorine content between 66 wt% and 69 wt% and by higher processing viscosity; in single-screw extrusion of CPVC pipe, screw torque increases by approximately 25–40% relative to PVC at the same melt temperature. At 67 wt% chlorine, the glass transition is approximately 117–125°C, leaving a narrow melt-processing interval before dehydrochlorination. The processing window is narrower than PVC: recommended stock temperatures are 195–215°C, and excursions above 220°C initiate dehydrochlorination. Gelation rate is measured by torque rheometry in a 60 cm³ mixer at 35 rpm; fast-fusing CPVC reaches 90% of maximum torque in 90–120 s, whereas slow-fusing resin requires more than 180 s. This parameter is critical on pipe extrusion lines operating above 800 kg/h, where stable gelation must occur within the first 12 L/D of the screw. Stabilizer selection is based on tin mercaptide systems rather than calcium-zinc only, because organotin stabilizers provide longer colour-hold at 200°C in CPVC pipe tests. The presence of copper or brass tooling is avoided because copper species catalyse dehydrochlorination; stainless steel or chrome-plated dies are specified for production runs.

Thermal degradation of CPVC proceeds by dehydrochlorination with an activation energy near 120–160 kJ/mol, depending on stabilizer type and chlorine distribution. In pipe extrusion, the residence time distribution between screw root and die exit must be kept below 3 min at melt temperatures above 205°C. A production-scale failure mode is the formation of black specks when stagnant resin accumulates in the barrel and undergoes autocatalytic dehydrochlorination; purging after every 8 h of continuous operation is specified on lines running above 500 kg/h. Post-chlorination of suspension PVC is carried out in aqueous slurry under ultraviolet light; the process increases chlorine content from 57 wt% to 66–69 wt% and raises the glass transition from approximately 82°C to 117–125°C. Base PVC with K-value 57–60 is typical for pipe-extrusion CPVC resin.

For specification-grade CPVC pipe compounds, incoming resin is tested for particle size distribution, thermal stability by dehydrochlorination at 180°C in nitrogen, and residual crystallinity. Unlike CPE impact modifiers, CPVC resin contributes to the polymer matrix rather than forming a dispersed elastomer phase. Supplier-to-supplier differences are observed mainly in particle morphology and fusion rate; these differences are not captured by single-point viscosity measurements alone.

In continuous PVC pipe and profile extrusion, CPE from different suppliers are not interchangeable at equal dosage when residual crystallinity differs. A 135A-type CPE with residual crystallinity 2–8% by DSC requires a lower processing temperature than a grade with residual crystallinity above 10%; the former also disperses earlier in the fusion zone. This difference reduces the risk of unmelted CPE particles at the die lip, a failure mode observed as surface roughness and low impact retention in production runs with undersized screen packs. Differences from chlorinated paraffin plasticizers are notable: CPE is a high-molecular-weight elastomer, whereas chlorinated paraffins are low-viscosity plasticizers that reduce modulus. Substitution of CPE by chlorinated paraffin in rigid PVC does not provide impact modification because the molecular weight is insufficient to form stress-relieving elastomer domains.

When Incoming Inspection Requires Compression Set and Sulfur-Cure Response Data

CSM grades require cure-response evaluation using a moving-die rheometer at 160°C for 30 min to record minimum torque, maximum torque, scorch time t_s2, and cure time t₉₀. Compression set after 22 h at 70°C by ISO 815-1:2019 is used to verify crosslink density and long-term sealing performance. In production-scale cable jacket extrusion, a CV line with 90 mm extruder and 180°C steam cure is operated at 15–30 m/min; the CSM compound is specified with a t₉₀ below 12 min to prevent under-cure at high line speed. If the CSM grade exhibits moisture content above 0.20 wt%, porosity can appear in the jacket wall; opened cold stock is dried at 60°C for 1 h. The CSM grades differ from CPE in that sulfonyl chloride groups provide a predictable metal-oxide cure without reliance on peroxide decomposition products. That difference is relevant where cable jackets must meet IEC 60502-1 low-voltage insulation thickness and heat-shock requirements because residual peroxide odour is eliminated from the curing system. CSM cured with 4 phr magnesium oxide and 2 phr pentaerythritol typically reaches 70 Shore A hardness and tensile strength above 10 MPa under ASTM D412-16.

In single-ply roofing membranes, CSM is calendered at 70–90°C roll temperatures and cured after incorporation of metal oxides. The membranes are specified to ASTM D4637 for vulcanized rubber sheet waterproofing; tensile strength after heat aging at 70°C for 168 h must retain at least 80% of original value. This end-use differs from CPE impact modification because the CSM phase must form a continuous elastomeric sheet rather than a dispersed modifier phase. In injection moulding of PVC fittings with CPE 135B at 6–10 phr, clamp force is set at 3–5 kN/cm² of projected area, and melt temperature is held below 195°C to avoid pre-gelation in the barrel. Screw-back pressure is maintained at 0.5–1.0 MPa; higher back pressure raises melt temperature and increases risk of CPE agglomeration. Short-shot failures have been observed when the melt viscosity is too high for thin-wall sections below 2 mm, which is why 135B rather than 135A is selected for such moulds.

Production-scale batch records for these chlorinated polyolefins show that lot-to-lot Mooney viscosity variation is controlled within ±5 points for CPE 135A and ±4 points for CSM grades, based on internal statistical process control limits. Sieve residue on 0.9 mm mesh is held below 2.0 wt% for powder CPE grades; oversized particles above that level cause screen-pack pressure rise in single-screw compounding. The products are incompatible with amine-based stabiliser packages when used as sole stabilizers in CPE-modified PVC because amine species can accelerate dehydrochlorination at processing temperatures above 190°C. These operational boundaries are derived from industrial process failures and are not a substitute for lot-specific certificate of analysis data.