Abstract: This article introduces common plastic packaging raw materials in detail, including low-density polyethylene (LDPE, LLDPE), high-density polyethylene (HDPE), etc. By explaining the performance characteristics and applicable scope of each raw material, combined with picture display, readers can have a deep understanding of the advantages and disadvantages of these plastic packaging raw materials, and provide a comprehensive reference for the selection of packaging materials. At the same time, some content cites authoritative external links to enhance the authority of the article to meet Google promotion requirements.
Performance characteristics
LDPE has good processing performance and can be quickly blown into bottles of various specifications in the blow molding process. It has good transparency, and small food packaging bags often use this material, which can make the packaging contents clearly visible. However, LDPE has poor air tightness and gas is easy to penetrate, so it is not suitable for pharmaceutical packaging with high requirements for air tightness; it has low tensile strength and is easy to break when subjected to large tensile force; its heat resistance temperature is not high, generally around 70°C, and it is easy to deform if it exceeds this temperature; its chemical and solvent resistance are not as good as high-density polyethylene, and it is easy to absorb oil and swell, causing the product to become sticky, such as when packaging oily foods.
Scope of application
It is often used in blow molding bottles and extrusion hoses, such as small soy sauce bottles, vinegar bottles and other condiment packaging, which can reduce costs and have a variety of shapes; LDPE is also commonly used in plastic bottles for external medicines because its transparency makes it easy to check the remaining amount of medicines. It is also used for container accessories such as bottle caps and bottle stoppers, various packaging films (such as disposable plastic bags are mostly made of LDPE), and can also be used as container and foam plastic cushioning materials, playing a cushioning and protective role in electronic product packaging.
(As shown in Figure 1, a small condiment bottle made of LDPE is shown)
Performance characteristics
LLDPE has similar impact strength and stress cracking resistance to high-density polyethylene, and can better resist bumps and collisions during transportation. Its transparency, hardness and processing performance are between high-density and low-density polyethylene, and its elongation and puncture resistance are the best among all kinds of polyethylene. When making cling film, this feature makes the cling film more durable.
Applicability
It is particularly suitable for packaging film, and its thickness can be 20% thinner than low-density polyethylene, reducing material costs and packaging waste. For example, many fresh food packaging films in large supermarkets are made of LLDPE, which can not only ensure packaging performance but also reduce costs. It is a very promising plastic packaging material. [External link: American Plastics Industry Association's introduction article on LLDPE](https://www.plasticsindustry.org/ll - dpe)
HDPE has good strength and heat resistance, with a maximum temperature of 120°C, and is suitable for containing liquid products that are sterilized at high temperatures. However, its transparency, elasticity and processing performance are poor, and its transparency is not as good as LDPE. It is not very suitable for packaging that requires clear display of contents; poor elasticity limits its use in packaging applications that require flexibility. HDPE has poor gas barrier properties and low gloss. It needs surface treatment before printing because its surface is smooth and ink is not easy to adhere to.
It is commonly used in containers and pallets, and large barrels are used for turnover packaging such as fresh milk and chemical products. In fresh milk packaging, its high strength and good heat resistance ensure that the packaging is intact during transportation and storage, and it has good chemical stability and will not react chemically with fresh milk; in chemical product packaging, it can withstand the corrosiveness of chemical products. HDPE is also often used in bottled yogurt and detergent bleach packaging. In yogurt packaging, its barrier properties prevent yogurt from being contaminated by the outside world, and its good molding properties can produce yogurt bottles of various shapes. In addition, it is also used for container accessories such as bottle caps and bottle stoppers.
EPE is divided into sheets, plates, pipes, rods and their split slice shapes, etc., which are widely used to package goods of any shape, especially for electronic products such as computers, TVs, stereos, speakers and other electrical appliances. Antistatic buffer packaging. Due to its good elasticity and toughness, it can effectively absorb vibration and impact, protect electronic products, and its antistatic properties can also prevent electronic products from being damaged by static electricity.
EPE is an environmentally friendly material. In addition to packaging, it can also be used to make life jackets, floats, travel bags, caps, etc. In the manufacture of life jackets and floats, its buoyancy and softness make it an ideal material. External link: Introduction to EPE on Environmental Materials Network
(As shown in Figure 3, it shows the scene of EPE packaging electronic products)
PP is the lightest of general-purpose plastics and has the highest heat resistance among general-purpose plastics. It can be used for a long time at 100℃~120℃ and is often used for food packaging and hot drink packaging that requires high-temperature sterilization, such as microwave-heatable food containers. It has high crystallinity, and its tensile strength and hardness are better than polyethylene, making the packaging more durable. PP has good moisture resistance, water resistance and anti-odor permeability. It can be heat-sealed to ensure the freshness and quality of food. It also has excellent bending fatigue resistance and can withstand acids, alkalis, salt solutions and most organic solvents below 80°C. For example, polypropylene packaging boxes can be used to package products containing chemical substances. However, PP has poor cold resistance and aging resistance. It is easy to become brittle at low temperatures and is easily aged by light and oxygen. It has poor air tightness and is not suitable for low-temperature use. It needs surface treatment before bonding or printing because its surface energy is low, which is not conducive to bonding and ink adhesion.
PP is widely used to make turnover boxes for food, chemical products, cosmetics, food and beverages, beer, etc. In the application of food turnover boxes, good strength and chemical resistance ensure that the turnover boxes are not damaged and do not contaminate food after repeated use; for chemical product turnover boxes, they can resist the corrosion of chemical products. Blow-molded bottles are used for packaging shampoo, cosmetics, etc., and good molding performance can produce various beautiful bottles. PP is also commonly used in threaded bottle caps or hinged packaging. Its good bending fatigue resistance ensures that the bottle cap is not easily damaged after multiple opening and closing. In addition, it is also used in woven bags, packaging films, strapping tapes, and foam plastic cushioning materials.
PS is colorless and transparent, odorless and non-toxic, and has good coloring and printing properties. It is widely used in product packaging that has high requirements for packaging appearance, such as transparent packaging boxes in food packaging, which can attract consumers by printing exquisite patterns. It has low water absorption, good dimensional stability, is rigid but not ductile, and has advantages when making packaging containers that need to maintain their shape. However, PS has low impact resistance, low surface hardness, and is easily scratched and polished, making it less suitable for packaging scenarios that are susceptible to collision and friction; it has poor moisture resistance and heat resistance, and is easily softened by many hydrocarbons, ketones, and higher fatty acids, which limits its application in special environments.
It is widely used to make small packaging containers such as boxes, cups, and tableware packaging films for food, pharmaceuticals, and daily necessities. In food packaging, transparent PS boxes can clearly display food and increase product appeal; in pharmaceutical packaging, its odorless and non-toxic properties meet the requirements. In addition, it is also widely used to make foam plastic cushioning materials, etc., and used for cushioning and shockproof packaging of instruments, meters, and electrical products. The light weight and cushioning properties of PS foam plastics can effectively protect products from damage during transportation.
PVC has good rigidity and hardness, and has advantages in making packaging containers that need to maintain shape and strength. For example, hard PVC pipes can be used to package small tools. Its heat resistance is poor, and its transparency can reach 76% to 82%. It is suitable for some products that require transparent packaging and do not require high heat resistance, such as toy packaging. PVC has excellent mechanical strength, wear resistance, and pressure resistance, and has good moisture resistance, water resistance, and air tightness. It can be heat-sealed, which is very important in the packaging of products that need to be sealed and preserved, such as cosmetics soft packaging. It has excellent printing performance and flame retardancy, and has advantages in packaging appearance design and safety requirements. However, PVC is resistant to strong acids, strong alkalis and non-polar solvents, but is easily corroded by polar organic solvents. It contains toxic vinyl chloride monomers, and the plasticizers and stabilizers used are mostly toxic substances. Polyvinyl chloride used for food and pharmaceutical packaging should use non-toxic additives, and the content of vinyl chloride monomer should not exceed 1ppm to ensure safety.
Manufacturing hard packaging containers, transparent sheets and soft packaging films. Transparent polyvinyl chloride sheets are thermoformed into various packaging containers, which are widely used in food and pharmaceutical packaging. In food packaging, transparent PVC containers can display food and attract consumers; in pharmaceutical packaging, good airtightness can ensure the quality of medicines. In addition, it can also be made into foam plastics and cushioning materials for shockproof packaging of some products.
PET has very good mechanical strength, good hardness, wear resistance and folding resistance. It performs well when packaging products with sharp corners or that need to be folded multiple times, such as electronic product packaging boxes. It has good heat and cold resistance, good moisture resistance, air tightness and excellent odor prevention. It can withstand weak acids, weak alkalis and most solvents, has good oil resistance, is suitable for printing, and is widely used in food packaging, beverage packaging and other fields, which can ensure the quality and taste of food and beverages. However, PET is not resistant to strong alkalis and strong acids, and chlorinated hydrocarbons also have an erosive effect on it; it is easy to carry static electricity, and there is no appropriate method to prevent static electricity, and the heat sealing performance is poor; the price is expensive, which to a certain extent limits its wider application.
It is mainly used to make packaging containers and films. Due to its good air tightness, heat resistance and cold resistance, polyester film is suitable for the packaging of frozen foods and steamed foods, which can ensure the quality of food under different temperature environments. Polyester bottles are widely used for beverage packaging. Most of the common mineral water bottles and carbonated beverage bottles on the market are made of PET. External link: International Packaging Association's research report on PET
PVDC is a strong material with a slightly light brown color. It has strong crystallinity, extremely low permeability to water vapor and gas, and has very good air tightness and moisture resistance. It is widely used in product packaging with extremely high requirements for moisture resistance and air tightness, such as high-end food packaging, which can effectively extend the shelf life of food. It has good mechanical strength, can withstand strong acids, strong alkalis and organic solvents, has excellent oil resistance, is self-adhesive, difficult to burn and has spontaneous combustion. However, it has poor aging resistance, is easily affected by ultraviolet rays, and is easy to decompose hydrogen. Its monomer is also toxic. When used in food packaging, the quality standards should be strictly controlled to ensure food safety.
Due to its excellent air tightness and moisture resistance, it is often used in products with extremely high packaging requirements, such as high-end medicines and food packaging, to ensure the quality of products during storage and transportation.
PA is a tough, opaque keratin material that is odorless and non-toxic. It has the smell of burning wool when burning. It has strong crystallinity, high melting point, oil resistance, general solvent resistance, and excellent mechanical properties. Its expansion strength and impact strength are significantly better than those of general plastics. It has good wear resistance, self-lubrication, and high bending fatigue resistance. It has good low temperature resistance and has advantages in packaging applications that need to withstand large external forces and low temperature environments, such as outdoor product packaging in cold northern regions. PA has better air tightness than polyethylene and polypropylene, is resistant to alkali and dilute acid, has no static electricity, and has good printing performance. However, it has strong water absorption, high moisture permeability, poor dimensional stability under high temperature conditions, and its air tightness drops sharply after absorbing water. Nylon is not resistant to formic acid, phenol and alcohols, and concentrated alkali also corrodes it.
It is mainly used for soft packaging of food, especially for packaging of greasy food, because of its good oil resistance, it can effectively prevent oil leakage, ensure the integrity of packaging and food quality. Nylon containers are also commonly used for packaging of chemical reagents, etc., taking advantage of its good chemical stability.
Under normal circumstances, PVA is not water-resistant, but it can be made water-resistant by heat treatment, aldehyde treatment or using appropriate organic matter to cross-link the molecular chains. It has good transparency and toughness, is odorless and non-toxic, has excellent air tightness and fragrance retention, has good mechanical strength, excellent stress cracking resistance, chemical resistance and oil resistance, does not carry static electricity, has good printing performance, and has heat sealing properties. It has advantages in food packaging and some product packaging with comprehensive requirements for packaging performance. However, PVA has high water absorption and moisture permeability, and is easily eroded by solvents such as alcohols and esters, which to a certain extent limits its application in special environments.
It can be used for food packaging to ensure the freshness and aroma of food. Water-based polyvinyl alcohol can be used for metered packaging of chemicals, etc. Its good molding performance and chemical stability can ensure the accuracy and safety of packaging.
EVA is better than polyethylene in stress cracking resistance, cold resistance, aging resistance and low-temperature heat sealing, and can withstand the corrosion of strong alkali and weak acid. It has advantages in packaging scenarios that need to be used and heat-sealed in low-temperature environments, such as frozen food packaging, and its low-temperature heat sealing can ensure the sealing of the packaging. However, EVA film has poor smoothness and is easy to stick; its moisture resistance is worse than that of low-density polyethylene, and its air tightness is poor; its heat resistance is poor; it is easily corroded by organic solvents such as strong acids, and can be dissolved in aromatic hydrocarbons or hydrocarbon substitutes; its oil resistance is poor. These shortcomings limit its application in product packaging with high requirements for moisture resistance, air tightness, heat resistance and oil resistance.
Used to make packaging film. Because of its good elasticity, it is suitable for wrapping pallets and can be tightly wrapped on pallets to protect goods. Because of its excellent low-temperature heat sealing properties, it is often used as a sealing layer of composite film. It is also used to make packaging containers for medicines and foods. It is more common in some low-temperature stored medicines and food packaging.
PC is colorless, with a transparency of up to 80% to 90%, and a refractive index of about 1.59. It is suitable for optical materials and has advantages in packaging applications that require high transparency, such as optical instrument packaging. It has good moisture resistance and air tightness, excellent fragrance retention and heat and cold resistance, outstanding impact toughness, the highest unnotched impact strength among thermoplastics, small molding shrinkage, low water absorption, good dimensional stability, no static electricity, excellent insulation performance, resistant to dilute acids, oxidants, reducing agents, salts, aliphatic hydrocarbons, etc., good oil resistance, and is widely used in electronic product packaging and other fields. However, PC is prone to stress cracking; poor bending fatigue resistance; poor heat sealing; not resistant to alkali, ketones, and aromatic hydrocarbons, and swells and causes stress cracking in many organic solvents. These shortcomings limit its application scope to a certain extent.
It is mainly used for electrical insulation materials and food packaging. It has good wear resistance and is suitable for packaging hardware and sharp objects.
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