Rotomolding Applications — The Complete Landscape

1. Rotomolding Industry Overview

Rotational molding (rotomolding) is a process that forms hollow plastic articles through biaxial rotation plus heating. Compared with injection molding and blow molding, rotomolding has low tooling cost and can form very large, complex parts in a single piece (volumes up to 50,000 litres and above), with no weld lines, low stress and uniform wall thickness — which gives it an irreplaceable advantage in the field of large outdoor plastic articles.

In 2025 the global rotomolding market was worth about USD 5.9 billion, and is expected to reach USD 11.2 billion by 2036 (CAGR 5.9%). Asia-Pacific accounts for 43% of the global total, with China the core growth engine (CAGR 7.4%). PE-type materials account for more than 85% of rotomolding resins; thanks to its toughness, wide processing window and excellent ESCR, LLDPE has become the preferred substrate for large water tanks and outdoor articles.

Typical application landscape

2. Why the Rotomolding Process Places Severe Demands on Additives

The rotomolding process itself means that its requirements on the additive system are far higher than those of ordinary plastics processing — it superimposes the two harshest conditions, "processing thermo-oxidative ageing" and "outdoor photo-ageing", on one and the same article.

2.1 Processing thermal oxidation

Rotomolding powder must stay inside a closed mould at 200–250℃ for 30–120 minutes, with oxygen continuously diffusing in. This means:

• The polymer is exposed to oxygen in the molten state for a long time → large numbers of free radicals are generated and the risk of thermo-oxidative degradation is very high
• The antioxidant system must combine sufficient initial antioxidant activity with long-term stability, otherwise the article has already "planted the seeds" of ageing the moment it leaves the mould
• The conventional synergy of a hindered phenol (such as AO-1010/1076) with a phosphite (such as AO-168) is the "standard base" for rotomolding

2.2 Outdoor photo-oxidation

More than 90% of rotomolded articles are used outdoors, continuously exposed to sunlight, rain, temperature differences and biological attack:

• UV-B (280–315 nm) directly breaks C–C / C–H bonds and triggers free-radical chain reactions; it is the main cause of surface chalking and cracking
• UV-A (315–400 nm) penetrates deeper and, together with heat and moisture, causes fading and discoloration
• UV absorbers (UV-A type) absorb and convert UV energy, while hindered amine light stabilizers (HALS) capture free radicals and can regenerate themselves — only the two acting together allow rotomolded articles to serve 10+ years even in high-UV equatorial regions

2.3 Chemical contact and extraction resistance

In scenarios such as water tanks, chemical tanks, pesticide drums and detergent containers, the article is in long-term contact with acids, alkalis, salts, oils and detergents:

• Low-molecular-weight light stabilizers are easily extracted by solvents → they fail quickly
• High-molecular-weight HALS (such as HS-944/HS-950) must be selected to ensure long-term stability
• NOR-type light stabilizers (HS-112 / XT-8) perform particularly well in acid, alkali and pesticide environments

2.4 Food-grade and drinking water compliance

Drinking water tanks, food turnover drums and children's toys must comply with regulations such as FDA 21 CFR and EU 10/2011:

• Additives must be listed on the FDA / EFSA indirect food-contact permitted lists
• Migration (SML) and specific migration limits must be met
• Tiangang HS-944 / HS-770 / AO-168 / AO-1076 and others have passed food-contact compliance in the main markets

2.5 Color stability and appearance

White, light-shade and colored articles must retain their initial appearance over the long term:

• Under high UV radiation they readily suffer yellowing, chalking and loss of gloss
• Light stabilizers with low color staining and low volatility are required (the combination HS-944 + UV-326/327 is recommended)
• Dark (carbon black) articles weather significantly better than light ones, but carbon black agglomerates easily and dispersion must be watched

2.6 Flame-retardancy requirements

Public facilities, children's playgrounds and electronic housings must meet flame-retardant grades such as UL94 V-0/V-2 and GB/T 2408:

• PE/PP substrates are inherently flammable and require flame retardants
• Traditional brominated flame retardants are restricted by RoHS and REACH; halogen-free flame retardancy is the trend
• Tiangang FR-810A polymeric halogen-free flame retardant combines high flame-retardant efficiency with low smoke and low migration

3. Common Failure Modes of Rotomolded Parts

4. Tiangang Proprietary Product Matrix (Core Rotomolding Recommendations)

4.1 Top recommendationHS-362 compounded light stabilizer package

4.2 Award-winningHS-625 high-molecular-weight polymeric hindered amine light stabilizer

4.3 Classic compositeHS-962 compounded light stabilizer package (light stabilizer 783)

4.4 Differentiated flagshipNOR light stabilizers XT-8 / HS-112

Selection guide: thick-wall moulding that needs dry-powder premixing → XT-8; liquid addition or masterbatch carrier systems → HS-112. Both can be used on their own, or compounded with HS-625 to form a "low-basicity dual-layer protection".

4.5 Scenario-specific compounded additive packages (selected by medium environment)

The Tiangang compounded additive package range is already segmented by medium environment and substrate, so rotomolders only need to match the environment in which the article serves and do not have to trial-blend themselves.

4.6 Light-stabilizing functional masterbatches (ready to use for small and medium rotomolders)

For small and medium rotomolders, functional masterbatches are the solution with the best return on investment — they save the weighing and blending steps, allow dust-free feeding and disperse better than direct powder feeding.

4.7 Three functions in oneFR-810A polymeric NOR halogen-free flame retardant

4.8 Rotomolding-specificAO-427 multifunctional processing aid

4.9 Tiangang own monomer products (package components / special customization)

The following Tiangang monomer products are used in rotomolding mainly as one component of a compounded additive package, or in the very special formulations for which Tiangang has not developed a ready-made package. For routine rotomolding projects please give priority to the proprietary products or packages in 4.1~4.8; where a genuine special need exists, Tiangang can build a custom formulation for the customer from its own monomers and provide complete validation data.

5. Recommended Formulations by Part Type

The table below gives the starting points of Tiangang proprietary product formulations for common rotomolding scenarios (based on LLDPE substrate and QUV-B artificial accelerated ageing). Every solution takes a compounded additive package or a Tiangang proprietary product as its main body, so customers do not have to blend several general monomers themselves. The specific dosage should be adjusted to the wall thickness, color, target service life and compliance requirements of the article.

6. Key Technical Parameters and Design Points

6.1 Additive addition sequence (to avoid antagonism)

At the premixing stage of rotomolding powder the recommended sequence is:

1. Resin powder + pigment / filler — high-speed mixing for 2 min
2. Tiangang compounded additive package (HS-362 / HS-962 / T series) added, mixing 3~4 min — the antioxidant components are already included, so there is no need to add hindered phenol and phosphite separately
3. Supplementary UV-A (if an ultra-high-temperature window is needed) added, mixing 2 min
4. Flame retardant FR-810A (if needed) added, mixing 3 min
5. NOR (XT-8 / HS-112, if the medium is acidic) added last, mixing 3 min and then discharging immediately

6.2 Processing window and thermo-oxidative control

• Mould surface temperature should be kept in the 220~240℃ range (PE); above 280℃ resin degradation accelerates
• Total heating time should not exceed 90 min (6 mm thickness); thick-wall parts need staged heating
• Slow cooling is recommended in the cooling stage (more than 30 min); too-fast cooling causes internal stress and stress whitening
• When the recycled material ratio is high, add AO-427 0.1~0.3% to suppress the rise in acid value, and at the same time raise the addition level of the compounded package

6.3 Color and surface post-treatment

• Colored articles (slides, planters, waste bins): add AO-427 0.1~0.2% to improve pigment dispersion and reduce batch-to-batch color difference
• White / light-shade articles: prefer the HS-362 or HS-962 package; where color control must be strict, choose HS-330 (low acid interaction)
• Black articles (carbon black 2.5%): carbon black itself is a strong UV screener, but high-molecular-weight HALS is still needed to prevent loss of gloss and chalking
• Pearlescent / metallic: pigments adsorb HALS, so the addition level of Tiangang proprietary packages must be raised by 20~30%, or a package with better dispersion should be selected
• Avoid using low-molecular-weight HALS alone as the main agent for white articles — migration and blooming will cause surface frosting

7. Tiangang's Differentiated Advantages

8. Application Cases and Customers Served

Tiangang additives have been used long-term in a number of large rotomolded part projects, all of them Tiangang proprietary product solutions:

• Large drinking water storage tanks (several municipal / engineering customers) — HS-362 package + UV-360 supplement, QUV 20k+ hours, 10-year warranty
• Chemical liquid storage tanks and acid liquid turnover containers — T-68 acid-resistant dedicated package, ready to use, zero trial-blending cost for the customer
• Pesticide drums and agricultural irrigation tanks — XT-8 NOR solution, sulfur resistance 3000~7000 ppm / chlorine resistance ≤ 850 ppm, solving the "premature failure" problem of sulfur-containing pesticides
• Large outdoor waste containers (sanitation projects in several northern provinces) — HS-962 package solution, no obvious color change outdoors for 8 years
• RV water tanks (export customers) — XT-8 + HS-625 high-weathering solution, passed FDA and EU food-contact certification
• Children's slides and playground equipment (public facility projects) — HS-362 + FR-810A halogen-free flame-retardant solution, UL94 V-2 passed, one grade satisfying both flame retardancy and weathering
• Automotive fuel tanks and intake pipes (automotive parts customers) — T-70 / T-81 automotive-specific granular package, meeting OEM weathering standards
• Marine floats and floating docks — XT-8 + HS-625 high-molecular-weight dual-layer protection, salt-spray extraction resistant