Yarn

Manufacturing Synthetic Yarn for Bike Bag’s Fabrics

Zooming in on fabrics, we see their interwoven yarns. And zooming in on an individual yarn, approaching the microscopic level, we see filaments twisted together to create that yarn. In this guide, we are examining the manufacturing processes that go into producing synthetic yarns, beginning with the preparation of the raw materials that go into the filaments and continuing through various processes to conclude with quality control of the finished yarn.

From the bicycle bag perspective, we are primarily concerned with yarn made from nylon, polyester or UHWMPE fibers. Beyond the type of polymer there are many other important phases in the yarn production process which can have substantial impact on the resulting fabric properties and the performance of the bike bags that these fabrics build.

***A few notes on this guide:

• Our goal here is to offer a general understanding of yarn manufacturing processes. Specific yarns will make use of a very specific combination of processes, some of which have not been explained here.
• Finishes, Coating, Dyes and Additives can be added at various stages throughout not only the yarn making process but also in the post-processing stages of the woven fabric. Here we indicate the stages at which they are commonly added.

Polymerization

The initial stage involves a process called polymerization, where small molecular building blocks are joined together to form long chain-like molecules.

• Raw Material Storage: Petroleum-based chemicals for nylon and polyester and ethylene gas for UHMWPE are held in large tanks.
• Mixing and Heating: Raw materials are transferred to large heating vats, combined in specific ratios and heated to high temperatures. Certain additives can be mixed with raw materials at this stage before the polymerization reaction begins. This is common for:
  • Catalysts: These help initiate and control the polymerization reaction.
  • Stabilizers: These prevent unwanted reactions during polymerization.
• Polymerization Reaction: Under carefully controlled conditions of heat and pressure, the small molecules start linking up, forming long molecular chains. At this stage other types of additives are introduced while the polymerization reaction is ongoing. This might include:
  • Chain Extenders: These help control the molecular weight of the polymer.
  • Crosslinking Agents: These create bonds between polymer chains for improved properties.
• Filtering and Purification: After polymerization, the molten polymer is passed through fine mesh screens or filters to remove impurities. This step ensures the resulting polymer is of high quality and free from defects.
• Post-Polymerization Additives: Certain additives can be introduced after the main polymerization reaction is complete, but while the polymer is still in a molten or easily mixable state. This stage is common for:
  • Colorants: Dyes or pigments to give the polymer its color.
  • Plasticizers: These improve flexibility and workability.
  • UV Stabilizers: To protect against degradation from sunlight.
• Cooling, Solidification and Pelletizing: After polymerization, filtering and additive mixing is complete, the mixture is pelletized. The molten polymer is fed into an extruder to form continuous strands. Exiting the extruder, the strands are immediately cooled in water or with air cooling before being passed into a pelitizer, a machine with rotating blades that cuts the solidified stands into small pellets or chips.
• Compounding: Additives can be mixed into the solid polymer pellets in a separate process called compounding. This involves re-melting the polymer and mixing in additives before re-pelletizing. This is often done for:
  • Reinforcing Fibers or Particles: Like glass fibers.
  • Specialty Additives: That might degrade under polymerization conditions.
• Collection and Storage: Polymer pellets are then collected and stored in large silos or bags, ready for the next stage of processing.

Filament Extrusion and Drawing

Polymer pellets are now processed into filaments. The different types of polymers used in bike bags require different versions of the extrusion process. Nylon and polyester are both processed into filaments in a melted molten state while UHMWPE is processed in a gel state. Other types of polymers used in the fabrics of bike bags require different extrusion processes, specifically, rayon, acrylic and spandex require wet spinning extrusion.

• Feeding the Hopper: Polymer pellets or chips are fed into a hopper, which funnels them into a screw extruder. The screw extruder is a heated barrel with a rotating screw that mixes and heats the polymer pellets as they move forward.
  • for Melt Spinning: Nylon or polyester polymer pellets are heated to a temperature controlled molten state.
  • for Gel Spinning: Solvent (commonly decalin or paraffin oil) is mixed in with UHMWPE polymer pellets. The combination of solvent and temperature controlled heat transforms the polymer into a gel like state.
• Extruding: The molten polymer (nylon or polyester) or polymer solution (UHWMPE) is forced through a spinneret, a device similar to a showerhead with many tiny holes. The shape and size of the spinneret holes determine the diameter and cross-section of the resulting filaments. The extrusion process forms continuous filaments as the material emerges from the spinneret.
• Solidification: The extruded filaments are cooled and solidified. This can be achieved through various methods, such as air cooling or passing the filaments through a coagulation bath (for solution spinning). The cooling process solidifies the polymer into fine filaments.
  • Cooling for Melt Spinning: This is typically done by passing the nylong or polyester filaments through a quenching chamber, where they are exposed to cool air or a water bath. This rapid cooling locks the polymer chains into place, forming solid filaments.
  • Coagulation for Gel Spinning: The extruded gel filaments are passed through a coagulation bath containing a non-solvent, such as water or alcohol. The non-solvent removes the solvent from the gel filaments, causing the UHMWPE to precipitate and solidify into continuous filaments.
• Drawing: The solidified filaments are drawn (stretched) to several times their original length. Drawing aligns the polymer molecules, which enhances the strength and elasticity of the fibers. Drawing is performed under controlled temperatures to optimize the molecular orientation.
• Heat Setting: The filaments are heated to a specific temperature while being held under tension. This step relaxes internal stresses and further aligns polymer chains, enhancing the tensile properties achieved during drawing.
• Finishing: Filaments are treated with chemical finishes or coatings in a solution or via a spray application. A variety of finishes can be applied at this stage. The finishes most typically applied now are:
  • Anti-Static Finishes: Reduces static electricity build-up during the next processing steps as well as for end use.
  • Lubricants: Reduces friction during subsequent textile processes such as twisting, cabling, or weaving.
  • Sizing Agents: Filaments are treated with sizing agents like polyvinyl alcohol (PVA) or starch-based solutions to add a protective layer, enhancing tensile strength and reducing breakage during weaving.
• Winding: Continuous filaments are prepared for the next stages of yarn production by carefully winding the drawn filaments onto spools or bobbins, ensuring that the filaments are organized, tensioned, and ready for further processing.

Processing Filaments into Yarn

Filaments are transformed into yarn through a variety of processes that play an instrumental role in determining the durability, water resistance, hand feel and appearance properties of the fabrics that they go into.

Yarn Types

A variety of types of yarns are utilized in the fabrics of bicycle bags. Our yarn type definitions refer to the the filament structure and the inclusion of high-tenacity properties. High-Tenacity yarns are made with filaments that have been drawn to align the polymer’s molecules. Standard yarns, which are not commonly used in bike bags, have not had their filaments drawn in the same way.

• High-Tenacity Multifilament Yarns: Made from multiple high-tenacity filaments twisted and sometimes cabled together. This is the most common type of yarn utilized in the nylon, polyester and UHMWPE fabrics that are used in bike bags.
• High-Tenacity Blended Yarns: Properties from both filaments are combined together in these yarns. Blended yarns can be manufactured by twisting the filaments of the different yarn types, plying multiple pre-twisted yarns or by cabling the pre-twisted and plyed yarns together. Though uncommon for these blends, the polymers can be melted and mixed together before extrusion.
  • Nylon and Polyester: This combination leverages the strength and elasticity of nylon with the UV resistance and water resistance of polyester. This yarn is typically manufactured by twisting nylon and polyester filaments together or plying pre-twisted yarns together.
  • Nylon and UHWMPE: This combination maximizes the exceptional strength and abrasion resistance of UHMWPE with the flexibility and resilience of nylon. This yarn is typically manufactured by either cabling pre-twisted yarns together.
  • Polyester and UHWMPE: This combination integrates the high tensile strength and abrasion resistance of UHMWPE with the UV stability and water resistance of polyester. This yarn is typically manufactured by either twisting filaments together or by cabling pre-twisted yarns together.
• Textured High-Tenacity Multifilament Yarns: A variety of texturing processes (see below) are used to add bulk and elasticity to high-tenacity multifilament yarns. Yarn texturing is also used to alter the appearance and hand-feel of the fabrics that they go into.
• Staple Fiber Yarns: Generally used in applications where a softer look and feel is desired. They are typically less abrasion-resistant compared to their filament counterparts. Their use in bike bags is limited to specific areas, such as linings or pockets.
• Standard Multifilament Yarns: Similar to staple fiber yarns in that these are utilized in lightweight application areas where softer look and feel is desirable. Standard multifilament yarn is our catch all for the non-high-tenacity versions of multifilament, blended and textured yarns that are infrequently used in bike bags.

***Include notes, maybe here? on Denier.

Yarn Manufacturing Processes

A wide variety of different types of manufacturing processes are used for processing filaments into yarns. A combination of some of these processes will go into the manufacturing of a given yarn.

• Texturing: This process involves modifying the surface and structure of the filaments, to impart bulk, elasticity, and hand-feel. This modification takes place before the filaments are twisted so that the desired texture can be uniformly carried into the subsequent yarn structures. Commonly used texturing techniques are air-jet texturing, false-twist texturing and mechanical crimping. Following texturing and before twisting, heat setting is typically used to lock-in the applied texture to the filament.
• Twisting: Twisting filaments together into a multifilament yarn is a closely controlled process that enhances strength, durability, elasticity, texture and other properties of the yarn. The tension, degree of twist, direction of twist and double twisting (twisting already twisted yarn in the opposite direction) are closely controlled factors to insure that the engineered specifications of the yarn are met. The number of filaments twisted into a yarn can vary broadly depending on the application.
  • Nylon: 10 to 200+ filaments per yarn.
  • Polyester: 20 to 300+ filaments per yarn.
  • UHMWPE: 1 to 100+ filaments per yarn.
• Plying: This process is used for the majority of yarns that are woven into bike bag fabrics. Plying involves twisting two or more single twisted yarns together to form a thicker, stronger yarn further enhancing its properties. The single twisted yarns, also known as plies, are twisted in the same direction (either S-twist or Z-twist), and this twist direction typically aligns with the original twist of the individual plies.
  • Nylon: 2-ply to 4-ply
  • Polyester: 2-ply to 3-ply
  • UHMWPE: 1-ply (monofilament) to 3-ply
• Cabling: This process further balances a yarn’s properties making it very robust and ready to be woven into highly durable fabrics. The cabling process twists multiple plied yarns together, typically in the opposite direction of the original ply twist.
  • Nylon: 2 to 4 cablings
  • Polyester: 2 to 3 cablings
  • UHMWPE: 2 to 3 cablings
• Heat Setting: After the final process of twisting, plying or cabling is applied to the yarn, heat setting locks-in and enhances the twisted structure and other properties of the yarn. Heat is applied through oven or steam chambers with different yarn types requiring different optimal temperatures.
• Finishing: Yarn are treated with chemical finishes, coatings and dyes through immersion or via a spray application. A wide variety of finishes can be applied at this stage which most commonly include:
  • Anti-Static Finishes: Reduces static electricity build-up during weaving.
  • Lubricants: Reduces friction during weaving.
  • Sizing Agents: Adds a protective layer to the yarn, increasing its strength and abrasion resistance during weaving. Sizing also helps in reducing yarn hairiness and improving the fabric’s final finish.
  • Water-Repellent Finishes: Increases the yarns hydrophobic properties, helping the final fabric resist water absorption.
  • UV Stabilizers: Protects the yarns from degradation caused by UV radiation, which can weaken fibers over time.
  • Yarn Dyes: While dyeing typically occurs at the fabric stage, dyeing the yarns before they are woven into fabric ensures deep and uniform coloration.
• Packaging: After the yarn is completed it is transferred to packaging for storage. This step involves carefully guiding it onto uniform, tension-controlled cones also called spinner’s packages. This process ensures that the yarn is evenly distributed and free of defects like tangles or inconsistent tension and ready for the first stage of weaving, the winding process.

Yarn Measurements

Yarn measurements are fundamental specifications used throughout the textile industry to define and standardize the key physical properties of yarns. These standardized measurements enable yarn manufacturers to maintain consistent production quality while allowing fabric manufacturers to select optimal yarns for specific fabrics. Yarn measurements provide crucial insights into how yarns will perform in fabrics, helping predict the final fabric’s properties. From this we can better understand why bike bag manufacturers utilize specific fabrics for different applications and performance requirements.

Denier (Linear Mass of Yarn)

The unit of measurement that expresses the linear mass density of yarn. It is defined as the mass in grams of 9,000 meters of yarn.

• Units of Measure:
  • Denier (D): grams per 9,000 meters. Commonly used in the US and Asia and for synthetic yarns.
  • Tex: grams per 1,000 meters. An alternative measurement to Denier, more commonly used in Europe.
  • 1 tex = 9 denier
• Example Fabrics with the Denier of their Yarn:
  • 70D Nylon Yarn
  • 210D Nylon Yarn
  • 500D Cordura® Nylon Yarn
  • 1000D Nylon Yarn
• Fabric Properties Influenced by the Denier of its Yarn:
  • Weight: Higher denier yarns produce heavier fabrics.
  • Durability: Higher denier often correlates with increased durability.
  • Texture: Higher denier yarns may produce fabrics with a rougher texture while lower denier yarns can allow for softer, more flexible fabrics.
• Denier’s Interconnection with Other Measurements:
  (The following comparison summaries are based on scenarios where only the listed measurement is altered and ALL other factors remain equal.)
  • to Multi-Ply Yarn = Strong, Direct Correlation
    Multi-ply yarn correlates to a higher denier with each additional yarn ply effectively multiplying the yarn’s denier.
  • to Thread Count = Strong, Inverse Correlation
    This is an inverse relationship. Higher thread count fabric correlates to a lower denier yarn.
  • to Fabric Weight = Strong, Direct Correlation
    Heavier fabric correlates with a higher denier yarn though the relationship is not proportional.
  • to Fabric Thickness = Strong, Direct Correlation
    Higher fabric thickness correlates with a higher denier. As denier is a measure of yarn thickness it directly affects a fabric’s thickness.
  • to Fabric Density = Strong, Direct Correlation
    Higher fabric density correlates to higher denier yarn, however the relationship can be complex as denier affect both mass and volume components of density.

Multi-Ply

Multi-ply refers to yarns made by twisting together two or more single yarns (plies) to form a stronger, thicker composite yarn.

• Units of Measure:
  • Number of Plies: Denoted numerically as 2-ply, 3-ply, 4-ply, etc., indicating the number of single yarns twisted together.
• Example Fabrics with their Yarn Ply:
  • 2-Ply 210D Nylon Yarn
  • 3-Ply 500D Polyester Yarn
  • 3-Ply UHMWPE Yarn
• Fabric Properties Influenced by Yarn Ply:
  • Durability: Often stronger than single-ply yarns, improving the fabric’s ability to withstand stress.
  • Texture: Can influence the feel of the fabric either making it smoother or more textured.
  • Structure: May be less elastic due to the increased thickness and twist.
• Multi-Ply’s Interconnection with Other Measurements:
  (The following comparison summaries are based on scenarios where only the listed measurement is altered and ALL other factors remain equal.)
  • to Denier = Strong, Direct Correlation
    A higher denier correlates with multi-ply yarn, with each additional yarn ply effectively multiplying the yarn’s denier.
  • to Fabric Thickness = Strong Correlation
    Higher fabric thickness correlates with multi-ply yarn, with each additional yarn ply adding to the thickness of the yarn and thereby the thickness of the fabric.
  • to Fabric Weight = Strong, Direct Correlation
    Heavier fabric correlates with multi-ply yarn, with each additional yarn ply multiplying the weight of the yarn and thereby the weight of the fabric.
  • to Yarn Twist = Strong Relationship
    While not directly correlated, yarn twist and multi-ply are highly interconnected because yarn twist is critical to ply integrity, structure and performance in multi-ply yarns.

Yarn Twist

The number of twists per unit length in a yarn given to it during the yarn manufacturing process. The twist help bind the fibers or plies together.

• Units of Measure:
  • Turns per Inch (TPI)
  • Turns per Meter (TPM).
  • Twist Direction: S-twist (left-hand twist) or Z-twist (right-hand twist).
• Example Fabrics with their Yarn Twist:
  • Low-Twist 70D Nylon Yarn (2 TPI)
  • High-Twist 500D Polyester Yarn (10 TPI)
  • Balanced Twist UHMWPE Yarn (4 TPI)
• Fabric Properties Influenced by Yarn Twist:
  • Durability: Generally increases with twist, up to a point and can increase abrasion resistance.
  • Structure: Influences the elasticity and flexibility of the yarn and the resulting fabric.
  • Feel: Higher twist often results in a harder yarn feel, potentially making it smoother or more rugged.
• Yarn Twist’s Interconnection with Other Measurements:
  (The following comparison summaries are based on scenarios where only the listed measurement is altered and ALL other factors remain equal.)
  • to Multi-Ply Yarn = Strong Relationship
    While not directly correlated, yarn twist and multi-ply are highly interconnected because yarn twist is critical to ply integrity, structure and performance in multi-ply yarns.
  • to Denier = Moderate Relationship
    While not directly correlated, denier and yarn twist are interconnected because both denier and yarn twist together determine the yarn’s diameter, structure, and other properties.
  • to Thread Count = Moderate Relationship
    While not directly correlated, thread count and yarn twist are interconnected because by adding bulk to the yarn, yarn twist influences the maximum achievable thread count.
  • to Fabric Density = Moderate Relationship
    While not directly correlated, fabric density and yarn twist are interconnected because by adding bulk to the yarn, yarn twist influences the fabrics density.