If your R-PET pellets have too low a viscosity for bottle preforms or technical parts, a solid-state polymerization reactor raises the molecular weight of the PET to the required level, without compromising the material's properties. The SSP process increases the intrinsic viscosity, improves the melting point, mechanical strength, and chemical stability, turning an ordinary pellet into high-performance material suited for food contact.
In the recycling flow, solid-state polymerization sits after pelletizing, as a quality-finishing step, where the material gains maximum value. It replaces dependence on expensive virgin PET with a high-IV R-PET pellet, produced from your own material. It integrates naturally into any plant that produces pellets for preforms, strapping, or technical parts. See the full range of PET recycling equipment and where each piece fits.
Key Advantages of a PET SSP Reactor
• Higher intrinsic viscosity, solid-state polymerization increases the molecular weight of the PET without affecting its properties, for a material eligible for preforms and technical parts.
• High purity, the process removes low-molecular-weight substances, residual monomers, and oligomers, so the finished pellet is cleaner and safer for food contact.
• Improved mechanical properties, higher melting point, superior strength and chemical stability, exactly what high-performance applications require.
• Controlled viscosity increase, yield of up to 0.02 per hour, with fine adjustment depending on the desired final viscosity.
• Modular, compact design, capacities of 12,000 L and 24,000 L, freely combinable depending on production, much more compact than traditional installations.
• Simple digital control, a friendly, easy-to-operate interface, with process parameters that are visible and repeatable from one batch to the next, for consistent pellet quality.
• Simplified maintenance and operation, the modularized construction makes maintenance and service much easier than with classic bulky systems.
• High-value recycled material, a high-IV R-PET pellet sells at a premium-material price, shortening the payback of the investment.
Technical Specifications, Solid-State Polymerization
| Parameter | Value |
|---|---|
| Process type | Solid-state polymerization (SSP) |
| Purpose | Increasing molecular weight and intrinsic viscosity |
| Operating temperature | 180–220 °C (below the melting point of PET) |
| Atmosphere | Inert gas (nitrogen) |
| Viscosity increase | Up to 0.02 per hour |
| Reactor capacities | 12,000 L and 24,000 L (modular design) |
| Control | Digital, friendly interface |
| Feedstock | R-PET pellets with low viscosity |
| Finished product | High-viscosity, food-grade PET pellets |
| Certification | Compliant with food contact requirements (FDA approved) |
Applications and Industries for Increasing PET Viscosity
Solid-state polymerization is the indispensable step in manufacturing PET bottle preforms, containers, packaging strapping, and other technical plastic products that require high-performance PET. The resulting high-viscosity pellet feeds directly into preform injection and strapping extrusion, replacing part of the virgin material. For a recycler, this means a pellet sellable at a premium price, not low-value goods.
The material obtained through solid-state polymerization meets the strict requirements for food contact; the high-IV R-PET pellet is compliant with Regulation (EU) 2022/1616 on recycled plastic materials intended for food contact.
Beyond packaging, high viscosity is essential for technical fiber, high-strength strapping, and engineering parts made from PET. For these applications, the pellet must have stable viscosity and high purity, exactly what a well-controlled solid-state polymerization reactor delivers. For producers who sell pellets, the jump from low IV to high IV completely changes the selling price.
The process removes residual monomers, oligomers, and low-molecular-weight substances, so the final pellet is not only stronger but also purer. This double improvement, viscosity plus purity, is the reason solid-state polymerization remains the reference technology for high-performance PET applications, from preforms for carbonated beverages to industrial strapping subjected to high tensile loads.
Compatible Materials
The solid-state polymerization reactor works with R-PET pellets from recycling, whether obtained through classic pelletizing or from crystallized flakes. The cleaner and better crystallized the incoming pellet is, the more uniform and efficient the viscosity increase.
| Accepted feedstock | Notes |
|---|---|
| Low-IV R-PET pellets | The main source for increasing viscosity |
| Pellets from bottle-to-bottle recycling | For finishing to food grade |
| Pellets for technical fiber | When higher mechanical strength is required |
| Pellets for packaging strapping | High IV for high-strength strapping |
How It Works
The solid-state polymerization process follows clearly defined steps, from the incoming pellet to the high-viscosity material:
1. Preliminary treatment, the pellets are dried to remove moisture, which would otherwise cause degradation reactions.
2. Heating, the material is gradually heated to near the melting point, between 180 and 220 °C, to promote the reaction.
3. Solid-phase polymerization, under controlled temperature and in a nitrogen atmosphere, the molecular chain continues to polymerize, and the molecular weight increases.
4. Cooling, the material is slowly cooled to room temperature, to avoid internal stresses caused by sudden cooling.
5. Post-processing, depending on requirements, the finished pellets are then sorted and packaged.
Because the parameters are digitized and repeatable, resuming a viscosity recipe is simple, and a new operator quickly reaches consistent results. As a result, a solid-state polymerization system stays predictable even in plants with staff turnover.
Frequently Asked Questions
What is solid-state polymerization used for?
It increases the molecular weight and intrinsic viscosity of the PET pellet, raising the melting point, mechanical strength, and chemical stability. It is the step by which an ordinary R-PET pellet becomes material suited for bottle preforms, packaging strapping, and high-performance technical parts.
By how much does viscosity increase per hour?
The viscosity increase reaches up to 0.02 per hour, with fine adjustment depending on the desired final value. The solid-state polymerization process simultaneously removes residual monomers and oligomers, so it also raises the purity of the material, not just the viscosity.
What capacities are available?
The reactors come in two sizes, 12,000 L and 24,000 L, with a modular design that can be freely combined depending on your production capacity. The compact, modularized construction makes maintenance much simpler than with traditional, bulky installations.
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 solid-state polymerization reactor 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.
At what temperature and in what atmosphere does the process take place?
The solid-state polymerization process takes place at controlled temperatures between 180°C and 220°C, below the melting point of PET, so the pellets remain solid. The reaction takes place in an inert nitrogen atmosphere, which prevents thermal degradation and oxidation of the material during the viscosity increase. The digital control keeps the parameters consistent from one batch to the next.
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 reactor 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.
