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Powering Shared Bicycles with Sustainable Airless Tires

Providing riders lightweight, maintenance-free, and eco-friendly bicycles

Shared bicycles are effective short-distance transportation tools with the advantages of reducing carbon emissions and alleviating traffic congestions. However, the requirements on tires of shared bicycles, such as, riding-comfort, reliability, cost efficiency, and sustainability, are difficult to meet. Air-filled tires are non-reliable with high maintenance costs due to frequent flat tires. Therefore, airless tires have become preferred solutions to shared bicycles today. SPECFLEX™ Microcellular Polyurethanes produce micron-sized foam structure that balances comfort, strength, and durability while enables new circular economy for air-less tires. Consequently, SPECFLEX™ provides riders lightweight, maintenance-free, and eco-friendly bicycles reducing carbon emissions and facilitates mobility (Figure 1).

Dow SPECFLEX™ Microcellular Polyurethanes enable reliable, comfortable, durable, and sustainable shared-bicycle business and eco-system

Bike tire recycle graphic

Figure 1. Dow SPECFLEX™ Microcellular Polyurethanes enable reliable, comfortable, durable and sustainable shared-bicycle business and eco-systems. (A) Scanning Electron Microscopy (SEM) image of Dow SPECFLEX™ Microcellular Polyurethanes, (B) Airless tires made from SPECFLEX™ Microcellular Polyurethanes, (C) the latest shared-bicycle model utilizing Dow SPECFLEX™ Microcellular Polyurethanes, (D) basketball playground made from granules of recycled air-less tires using SPECFLEX™ Microcellular Polyurethanes in 2020 (Guangzhou, China).

What does SPECFLEX™ Microcellular Polyurethanes do?

SPECFLEX™ Microcellular Polyurethanes were molded into 24-inch airless tires with density around 600 kg/m3 (ca. 950 g for each tire) and then mounted onto the wheels of shared bicycles. The air-less tires from SPECFLEX™ Microcellular Polyurethanes eliminate flat-tire risks and bring excellent riding-comfort to riders. Dow SPECFLEX™ Microcellular Polyurethanes are breakthrough products in this field and have been applied to over 3-million bicycles (Figure 2).

New shared bicycles launched with Dow SPECFLEX™ Microcellular Polyurethane tires

Rows of public bicycles

Figure 2. New shared bicycles from (A) Meituan (Mobike) and (B) Hellobike with Dow SPECFLEX™ Microcellular Polyurethane tires.

Different from alternative polyurethane tires that become environmental burdens after service (Figure 3),
SPECFLEX™ Microcellular Polyurethanes can be recycled into new applications thanks to patent-pending novel molecular structures (Figure 4).

Airless tires made from problematic materials showed limited recyclability due to inferior material properties and caused urgent environment issues

Pile of bicycle tires

Figure 3. Shared bicycles with (A) TPEE airless tires and (B) Dow first-generation microcellular polyurethane air-less tires. (C) Wasted tires with limited recyclability due to inferior material properties caused urgent environment issues. The inserted images in the upper-right corner of panel (A) and (B) illustrate the wear of tires.

Basketball playground made from granules of recycled SPECFLEX™ Microcellular Polyurethanes airless tires in 2020 (Guangzhou, China)

Granules chart

Figure 4. (A) Basketball playground made from granules of recycled SPECFLEX™ Microcellular Polyurethanes air-less tires in 2020 (Guangzhou, China) and (B) illustration of tire granule layer.

How does SPECFLEX™ Microcellular Polyurethanes operate?

SPECFLEX™ Microcellular Polyurethanes apply patent-pending (PCT/CN2019/097011, PCT/CN2019/097014, PCT/CN2020/101771, and PCT/CN2020/102012). Its unique properties, shown in Figure 5, arise from a multi-component system that includes (1) breakthrough ester/ether hybrid structures with unique molecule weight and microstructures, (2) a series of modified isocyanates with variable molecular structure, functionality and molecular weight, (3) a series of standard polyether polyols with variable functionality, molecular weight, structure, and filler content, and (4) additives related to blowing, gelling, appearance, and etc.

Formulated systems employing Dow SPECFLEX™ Microcellular Polyurethane technology uses four components to create a microcelluar polyurethane material with exceptional properties and recyclability

Microcellular Polyurethane

Figure 5. Formulated systems employing Dow SPECFLEX™ Microcellular Polyurethane technology uses four key components to create a microcellular polyurethane material with excellent tear-resistance, heat stability, internal heat management, abrasion-resistance, weather-ability and recyclability.

Why SPECFLEX™ Microcellular Polyurethanes?

Dow SPECFLEX™ Microcellular Polyurethanes are advanced microcellular polyurethane foams for airless tires in shared bicycles. It provides superior performance compared to alternative technologies, including;

  • Enhanced Performance – exceptional performance for superior riding experiences in shared bicycles with safety, comfortableness and durability (Figure 6).
  • Sustainability – breakthrough technology enabling recyclable tires of shared bicycles (Figure 7).
  • Improved Processability – 10% reduction in rate of defective tires.
  • 20% lower in cost.

Performance comparison of Dow SPECFLEX™ Microcellular Polyurethanes and products from Dow's first generation and competitor airless tires of shared bicycles

Performance comparison

Figure 6. Performance comparison between Dow SPECFLEX™ Microcellular Polyurethanes and products from Dow’s first-generation and competitor for airless tires. Dow SPECFLEX™ Microcellular Polyurethanes show exceptional performance in attributes of tear-resistance, heat-stability, internal heat management, abrasion-resistance, and recyclability, while maintaining good weatherability.

Tensile strength of samples made from tire granules of fresh tires and recycled tires using standard VORAMER™ MR 1045L as binder

Tensile strength chart

Figure 7. Tensile strength of samples made from tire granules of fresh tires and recycled tires from various products using 25 wt.% of Dow standard VORAMER™ MR 1045L as binder.