If you want to increase the viscosity of recycled PET without cooling and reheating the material, a liquid-state polymerization installation raises the molecular weight directly in the molten phase. The process takes low-viscosity PET (flakes, sheet, fiber, or low-IV pellets) and delivers high-quality material for fiber, packaging strapping, pellets, and sheet, much faster than the solid-state option.
Unlike SSP, liquid-state polymerization works with the polymer already molten, so it completely eliminates the cooling step and the reheating step. The reaction in the molten phase is considerably faster than in the solid phase, which translates into lower energy consumption and a more compact flow. See where this technology fits in the full range of PET recycling equipment.
Key Advantages of a PET LSP Reactor
• Cage-type reactor, shaftless, the axless design eliminates material buildup on the shaft, the classic problem of central-shaft reactors, and extends the equipment's lifetime.
• Large reaction surface, the cage-type geometry provides a much larger film-forming area, so a strong viscosity increase and efficient removal of impurities.
• Good liquid-level control, unlike the ordinary reactor, where a low level is hard to maintain, the LSP reactor keeps a short, consistent melt residence time.
• No cooling and reheating, liquid-state polymerization keeps the material molten, so no energy is consumed to cool it and then reheat it, as with SSP.
• Fast reaction in the molten phase, the reaction time in the molten phase is much shorter than in the solid phase, which raises productivity per hour.
• Better economics, eliminating the thermal cycle and the high speed make liquid-state polymerization an alternative with lower operating costs than SSP.
• Superior-quality recycled material, through liquid-state polymerization, low-IV PET yields high-grade fiber, strapping, pellets, and sheet, that is, products sellable at a premium price.
• Robust construction, simple maintenance, with no central shaft to clean and fewer blockage zones, service interventions are rarer and easier.
Technical Specifications, Liquid-State Polymerization
| Parameter | Value |
|---|---|
| Process type | Liquid-state polymerization (molten phase), intrinsic viscosity increase |
| Reactor type | Cage-type LSP reactor, no central shaft |
| Feedstock | Low-IV PET: flakes, sheet, fiber, fabric, low-IV pellets |
| Finished product | PET fiber, packaging strapping, PET pellets, high-grade PET sheet |
| Operating mode | In the melt, with no cooling-reheating cycle |
| Reaction time | Considerably shorter than in the solid state |
| Liquid-level control | Precise adjustment, short melt residence time |
| Reaction surface | Large (cage-type geometry), efficient film formation |
| Capacity | Configurable per project |
Applications and Industries for Molten-Phase Polymerization
A liquid-state polymerization installation serves recyclers and producers who want to turn low-viscosity PET into high-value material. The resulting high-IV melt goes directly into polyester fiber spinning, into the extrusion of high-strength strapping, and into the production of pellets and sheet. For a producer, this means high-margin products instead of low-quality goods.
Recycled material upgraded through liquid-state polymerization can reach regulated applications; for food-contact uses, recycled plastic material is governed by Regulation (EU) 2022/1616 on recycled plastic materials intended for food contact.
Beyond fiber and strapping, liquid-state polymerization is used for valorizing polyester textile waste, fabrics, and reject yarns, sources that are otherwise hard to process. The cage-type reactor tolerates these difficult materials and raises their viscosity to the level required by industrial applications. For those who sell fiber or strapping by the ton, the quality jump brought by well-controlled liquid-state polymerization completely changes the selling price of the output.
Compatible Materials
The LSP reactor is designed for difficult, low-viscosity materials that other processes handle with difficulty. It accepts a wide range of recycled PET, from bottle flakes to textile waste, and the cage-type geometry ensures a uniform viscosity increase even for non-homogeneous materials. The better cleaned the incoming material, the more consistent the result.
| Accepted feedstock | Notes |
|---|---|
| PET film and sheet | Including waste and perforated film |
| Flakes from PET bottles | Washed post-consumer material |
| Polyester fibers and fabrics | Textile waste otherwise hard to process |
| Reject yarn (waste yarn) | From textile production |
| Low-IV PET pellets | For raising the viscosity to high grade |
| PET packaging strapping | Reject and recovered material |
How It Works
The flow on a liquid-state polymerization installation is continuous and takes place entirely in the molten phase:
1. The low-IV PET (flakes, sheet, fiber, or pellets) is fed and melted in the extruder, under temperature control, at the start of the liquid-state polymerization process.
2. The melt is filtered to remove solid contaminants, before entering the reactor.
3. The molten material enters the shaftless, cage-type reactor, where a thin film forms over a large surface.
4. In the reactor, under vacuum, viscosity increases rapidly, and the volatiles and low-molecular-weight impurities are extracted.
5. The liquid level is precisely controlled, maintaining a short, uniform melt residence time.
6. The high-IV melt is directed straight to spinning, strapping extrusion, pelletizing, or sheet production.
Because everything happens in the melt, there is no pause for cooling and reheating, and the material reaches the finished product faster. A continuously monitored liquid-state polymerization line maintains consistent melt quality and quickly brings new operators to stable results, a real advantage in plants with staff turnover.
Frequently Asked Questions
How does liquid-state polymerization differ from SSP?
The essential difference is that liquid-state polymerization works with the molten polymer, while SSP keeps the pellets solid. This eliminates the cooling and reheating cycle, and the reaction in the molten phase is considerably faster than in the solid phase. The result is higher productivity and lower energy consumption, which is why many flows choose LSP as an economical alternative to SSP.
Why is the cage-type reactor better than an ordinary one?
The cage-type, shaftless reactor provides a much larger reaction surface and superior film-forming efficiency. In addition, the lack of a central shaft eliminates the material buildup that occurs in classic reactors and extends the equipment's lifetime. Good liquid-level control maintains a short melt residence time, which means a strong, consistent viscosity increase in liquid-state polymerization.
What materials can be processed?
The system accepts PET film and sheet, waste and perforated film, polyester fibers and fabrics, reject yarn, bottle flakes, and low-IV pellets. This flexibility makes liquid-state polymerization a suitable solution for valorizing textile waste that is hard to process by other methods.
Is the delivered equipment new?
Yes. We deliver new, unused equipment, built to order, not refurbished units. The construction uses components from established suppliers, with CE marking where applicable, and every unit undergoes a complete inspection before shipping. You receive the technical documentation and operating manuals in your language, for a commissioning without surprises and predictable long-term operation.
What makes URSTAG a premium brand?
European design, top-tier components and experience. Every machine is designed by our engineering teams in Europe and built from components by industry leaders such as Siemens, Schneider Electric, ABB, WEG, SEW-Eurodrive, NORD Drivesystems and Bonfiglioli. The result is reliable, energy-efficient and durable equipment, backed by over 15 years of experience and by delivery, installation, training and service included.
How long does installation and commissioning take?
Transport, commissioning, and operator training are included and carried out by a local team, in your language. Before shipping, the installation undergoes a free inspection, so your unit becomes operational quickly, with no hidden installation costs.
Why URSTAG?
URSTAG is a premium brand of recycling equipment, with over 15 years of experience. You don't just get a machine, you get a solution engineered by specialists, built from top-tier components and backed by a team that supports you from design through commissioning.
• European engineering, every machine and every complete line is designed by our engineering teams in Europe, with a focus on reliability, safety and energy efficiency.
• Premium components, we build on motors and automation from industry leaders: Siemens, Schneider Electric, ABB, WEG, SEW-Eurodrive, NORD Drivesystems and Bonfiglioli.
• Over 15 years of experience, we know how materials and machines behave in real-world operation, and we configure each solution for your flow and volume.
• New equipment, configured for you, we supply new units, made to order for your application, with complete technical documentation.
• Delivery, installation and training included, we handle transport, commissioning and operator training, with support throughout the equipment's life.
As a premium brand, URSTAG relies on European engineering, top-tier components and experience. You choose a partner that supports your production long term, with equipment built to run reliably in demanding industrial environments.
