This article contains an in depth look at plastic baggies.
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A plastic baggie is a flexible and pliable sack or pouch made from polymer materials. Commonly used for storing food, electronics, pharmaceuticals, and in shipping and retail displays, plastic baggies have become an essential and ubiquitous form of container.
The widespread use of plastic baggies can be attributed to their versatility, low cost, and ease of recycling. With billions of applications, their popularity surged in the 1960s following the introduction of the concept by a Swedish engineer, despite plastic's earlier industrial use during World War II.
Lightweight, durable, and convenient, plastic baggies are ideal for transporting lightweight items such as groceries, which contributed to their rapid adoption.
Initially seen as an environmental hazard, advancements in recycling technology have mitigated these concerns by allowing polymers to be reprocessed and reused. Increased public awareness has also contributed to a more responsible approach to plastic bag usage and disposal.
Though baggies have an industrial and commercial use, they are commonly found in homes where they are used for storage. The normal size of plastic baggies is between one quart and a gallon. Most baggies are small and compact, with larger types available for industrial packaging and storage.
Plastic baggies are constructed from a single polymer, reflecting their straightforward design. The manufacturing process is equally simple, focusing on the careful selection of polymer materials. Although many polymers exist, only a few are chosen for plastic baggies.
Polymers used in plastic baggies are derived from petroleum and come in granular or pellet form. During the polymerization process, color can be added to achieve the desired hue.
Selecting the right polymer is crucial in plastic baggie manufacturing. The choice of material relies on a thorough understanding of various polymers, each offering distinct characteristics and benefits for the final product. The four main types used in baggie production are polyethylenes, which are available in high, medium, low, and linear low densities.
Polyethylene is the most widely used polymer due to its excellent chemical and impact resistance, electrical properties, and low friction coefficient. In addition, it is lightweight, can easily be shaped and processed, and has zero moisture absorption. Polyethylene has a variable crystalline structure and is produced by the polymerization of the ethylene monomer. The chains for polyethylene molecules can be very long, up to as many as 500 subunits.
The selected polyethylene is blended with a lower density polyethylene in a mixer to create a uniform material. The mixing process varies depending on the type of baggie being produced. The choice of mixer is determined by the viscosity and shear requirements of the thermoplastic. Multi-shaft mixers and planetary mixers are frequently used for this purpose.
The plastic resin mixture is melted under carefully controlled conditions until it reaches a molten, pliable state. The resin must be heated to a temperature between 350°F and 410°F, ensuring it is sufficiently malleable for compression and shaping. The melting process is meticulously managed to prevent the resin from burning.
Once the resin pellets are pliable, they are extruded through a circular die, which controls the thickness of the bags. Air is blown into the molten material to create a long inflated tube. As the blown material reaches the top of the extrusion tower, it is pinched off at one end and then stretched and pulled to achieve the desired size and thickness.
During the extrusion process, the inflated bubble of plastic is gradually cooled as it stretches upward, ensuring that it maintains the desired thickness.
As the bubble rises, a series of rollers flatten it and transport it from the top of the tower to a set of collection rollers, as illustrated in the image below. The light blue lines indicate the flattened polymer material being guided to the blue rolls at the bottom of the image.
After reaching the rolls, the material is prepared for further processing into plastic baggies. Each full roll of film weighs over 300 lbs and can produce more than 30,000 bags.
In the conversion department, the rolled film is unwound and processed into bags. This stage involves shaping, forming, and sealing the bags using specialized machinery. Any excess film is collected for recycling. Additional features like gussets, handles, and zipper seals are also incorporated during this phase.
Printing can be done either before conversion, while the film is still on the roll, or after the bags are formed. The ink used is a specialized mixture applied using rollers, with each color applied separately by a different roller if multiple colors are used.
Wicket bags are stacked plastic bags held together by a thin metal rod known as a wicket, similar to those used in cricket. This design facilitates quicker and easier dispensing of the bags.
A specialty machine used in the conversion process is the side seal machine. This machine employs various attachments to create features such as bottom gussets, inside or outside lips, punch handles, perforations, and tape applications for courier bags. The image below illustrates examples of the different shapes and features that a side seal machine can produce.
Bottom seal machines eliminate the need for manual sealing of bag bottoms and can seal up to 200 bags per minute. The machine processes a rolled web of printed film, cutting and sealing it automatically.
T-shirt bag machines are specifically engineered to cut and hot seal the bottoms of T-shirt bags. They can produce various types of T-shirt bags, with or without gussets, and in different widths and lengths. A crucial feature of these machines is their capability to handle any type of polymer material. Additionally, precise placement of printing on the bags, ensuring it is centered and correctly positioned, is essential.
In the conversion process, bags were once cut manually using a heated knife, which also sealed the bag during cutting. With advancements in technology, machines now handle both cutting and sealing, offering greater speed and precision.
Baggie cutting machines are computer-controlled, with the bag dimensions programmed into their system. These machines manage cutting speeds based on bag size and material type, and they include tracking systems to ensure accurate sealing and cutting to the correct length.
There is a broad range of polymers available for manufacturing plastic baggies. Selecting the right polymer is crucial to ensure that the bags are suitable for their intended application. Each polymer type has unique characteristics and properties tailored to meet the specific requirements of various uses.
Though there are many varieties of available polymers, in the case of plastic baggies, the polymer that is used the most is a version of polyethylene. Polypropylene is also used to manufacture plastic baggies due to its exceptional strength and endurance.
HDPE is an excellent material choice for plastic baggies due to its lightweight nature, transparency, moisture and heat resistance, and high tensile strength. It is approved by both the United States Department of Agriculture (USDA) and the Food and Drug Administration (FDA) for food handling.
This federal approval has increased HDPE's use in food storage across homes and commercial settings. A key advantage of HDPE is its ability to be repurposed and recycled effectively.
Each type of plastic has a symbol indicating its material composition. For HDPE, the symbol below identifies it as a highly recyclable polymer.
MDPE is known for its clarity, though it is less transparent than low-density polyethylene. This material is not very strong or elastic, making it suitable for carrying light loads and items that won’t easily puncture it. MDPE exhibits strong resistance to acids, oxidants, and reducing agents and has low water absorbency, similar to other polyethylene materials.
MDPE's ability to melt when heated makes it highly recyclable. It can be reheated, melted, and remolded multiple times without losing its properties.
LDPE is a transparent polyethylene with moderate strength and flexibility. It is highly versatile and commonly used for sealing due to its low melting point. LDPE is soft, pliable, and lightweight, offering good low-temperature flexibility, toughness, and corrosion resistance. Its high impact and chemical resistance make it suitable for storing items at very low temperatures.
LDPE is recycled by being melted and formed into plastic sheets, which are sold to plastic manufacturers as raw material. There is a wide variety of places where LDPE can be dropped off for recycling from curbside pickup to grocery store drop off bins.
The symbol for LDPE is shown below, indicating its application as a manufacturing material.
LLDPE features a thinner gauge compared to LDPE but maintains the same level of strength. It can serve as a replacement for LDPE bags without sacrificing quality. LLDPE exhibits unique melt flow properties, remaining more viscous during extrusion. It offers high tensile strength, impact resistance, and puncture resistance, along with excellent stretching flexibility. This allows for the production of thinner plastic film with enhanced toughness and resilience.
Like other polyethylene materials, LLDPE is readily recyclable for the creation of additional plastic products.
PP bags have exceptional strength and resistance to chemicals, as well as excellent endurance and long shelf life. PP bags are ideal for storing materials that may be in storage for long periods. They are clearer than polyethylene bags, making it easier to see the contents, and have been approved by the FDA and USDA.
Unlike polyethylene polymers, polypropylene (PP) is derived from a propylene monomer and is a linear hydrocarbon resin. It is one of the most cost-effective plastics available. Known for its durability, strength, and light weight, PP is used in a diverse range of products beyond just plastic baggies.
Polypropylene is low in toxins and heat resistant, making it suitable for applications involving direct contact with food, as it does not release harmful chemicals. This characteristic makes it ideal for long-term food storage. The symbol for PP, which is displayed on bags made from this material, can be seen below.
One distinctive production method for PP is the creation of woven PP plastic bags. In this process, PP film is drawn into tape and then woven, resulting in a highly durable fabric used in the manufacturing of heavy-duty plastic bags.
Plastic baggies have become an integral part of daily life, serving a multitude of purposes such as storage, packing lunches, product sales, and safeguarding sensitive equipment. Their versatility has led to the creation of numerous specialized baggies tailored to specific applications.
Despite their small and compact size, baggies often outperform other soft-side containers in various tasks. Their key attributes—durability, strength, and affordability—make them exceptionally valuable.
Food safe bags are designed to be both sturdy and secure. They serve the primary function of storing food to keep it fresh for future consumption. For a bag to be deemed food safe, it needs to be resilient against the conditions of storage and should not pose any risk of contaminating the food. In addition to these critical attributes, convenience and accessibility are also important for food-safe plastic bags. Typically, these bags are made from transparent plastic that is heat-sealed to prevent microbial contamination.
Baggies with gussets are able to expand to allow for easy insertion of items. Gussets are slits along the sides, bottom, or sides and bottom of the bag. They lay flat until the bags are opened, and items are placed inside. Once opened, the bag will double or triple its width to match the items being placed in it.
Gusset bags offer remarkable versatility and adaptability for a wide range of uses. Whether you're storing tools, food, clothing, or various other items, these bags can handle them all, with their primary constraint being size. Available in numerous dimensions, gusseted bags cater to different needs and applications.
Displayed below is an illustration of a gusseted bag, highlighting its length, width, and depth.
Barrier bags are crafted from exceptionally robust materials designed to shield their contents from various threats. They provide protection against moisture, dirt, contaminants, and microorganisms, making them ideal for safeguarding valuables. Constructed from heavy-duty polymers, these bags are resistant to impact, punctures, and odors. Often, they are tailored to meet the specific needs of industrial applications.
While barrier bags can be transparent to allow visibility of the contents, they are also available in a range of colors to facilitate coding and organization of the materials within.
Biohazard bags are designed to safeguard their contents and ensure the safety of individuals in proximity. These bags feature pre-printed symbols to indicate that they contain hazardous materials. For specimen handling, biohazard bags often include an attached pouch for documentation, keeping paperwork separate and protected from the contents. Additionally, the exterior may feature check boxes for tracking, recording information, and processing.
Food safe bags are crucial for maintaining the freshness and safety of stored food. They must be both durable, to endure the conditions of storage, and secure, to prevent contamination of the food. These essential features ensure that the bags fulfill their primary purpose. Additionally, convenience and ease of access are important qualities for food-safe plastic bags.
Among various types of plastic bags, food safe options are highly popular. These bags are crafted from clear plastic and are heat-sealed to protect against microbial contamination.
Hanging plastic bags feature a punched hole at the top of the flap, enabling them to be hung from pegs or displays. Typically, these bags include a zip seal positioned just below the hang hole. Alternatively, some hanging bags have the hole at the bottom and are designed to hang upside down. This design allows users to access and reseal the bag while keeping it suspended.
Header plastic bags are designed for display purposes, featuring a header seal with a hanging hole for retail presentation. These bags are commonly used for product sales and include printed information on the header area. Available in a range of sizes and colors, header plastic bags can be customized to suit various products. The header typically measures one to two inches in height, with the bag seal positioned just below it, similar to hang hole bags.
Reclosable or resealable plastic bags, made from LDPE plastic, are available in two main types: grip and seal. These bags come in various thicknesses to accommodate the storage requirements of different objects, temperature conditions, and storage durations.
Grip: Grip resealable bags feature a grip at the top, making them easy to open and close. Their user-friendly design has made them a popular choice in the medical field for storing cotton and gauze swabs.
Seal: Seal bags have been a staple for years, commonly used in lunchrooms. They feature a zipper-style seal that can be engaged with the thumb and forefinger. Available in various colors, the color-coded seal indicates whether the bag is fully closed, providing an additional layer of safety.
Plastic bags offer a multitude of uses due to their durability and strength. Whether for storing parts in an assembly or adding a special touch to someone's lunch, these versatile bags meet a wide range of needs and have become an essential tool. Despite some negative perceptions, plastic bags remain a valuable solution for saving, storing, and shipping items, as well as transmitting information.
One of the primary advantages of plastic bags is their versatility and ability to be reused for various purposes. This characteristic sets them apart from other types of containers.
Plastic bags are widely used for storage due to their durability, effective sealing, and ability to contain various materials. They are commonly found in various areas of the home, including the kitchen, workshop, and playroom. In industrial settings, plastic bags are utilized for organizing small parts and tools, as well as for facilitating the transfer of items between departments.
Some items can spread, break, or damage other contents when packaged together. To manage these unstable items and ensure their safety, plastic bags offer an effective solution. Whether dealing with a jar of liquid or small components, plastic bags can securely contain and protect the contents, preventing spills and damage.
Plastic bags are ideal for protecting documents from atmospheric contamination, microbes, and moisture, whether they are being sent, stored, or have historical value. These bags are commonly used to safeguard photos, envelopes, greeting cards, and other written or printed materials. The tight seal and robust construction of plastic bags make them an excellent choice for preserving and securing important documents.
An interesting application of plastic bags for document protection comes from hunters. To shield their tags and licenses from rapidly changing weather conditions, hunters often place these important documents inside plastic bags to keep them safe and intact.
Professional organizers and efficiency experts frequently use small plastic bags to group items during organization projects. Whether dealing with unclassified items or miscellaneous pieces, plastic bags provide an efficient solution for categorizing and sorting. Their convenience and accessibility make it easy to manage and organize loose items into cohesive groups.
Plastic bags serve as a protective barrier for hazardous or dangerous items such as medications, ammunition, sharp tools, and powders. Their sturdy construction helps contain and control these unsafe items while clearly indicating their location. In addition to their organizational benefits, using plastic bags to store hazardous materials enhances safety and organization.
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