Even though the densities of LDPE and LLDPE (0.921 – 0.926 g/cc) are similar, LLDPE displays better tear and impact film properties than LDPEVery flexible, natural milky color, translucent with high impact strength. Excellent for mild and strong buffers, good chemical resistance. Good water vapor and alcohol barrier properties. Poor gas barrier, sterilizable with EtO (EtO stands for Ethylene Oxide, a toxic, cancer causing gas, which is used to sterilize most of plastics) or gamma radiation. Good stress crack and impact resistance. 

Blends of branched (LDPE) and linear (LLDPE) low density polyethylene blends are normally used in plastic film manufacturing. This is done in order to achieve advantageous properties inherent to the combination of both resins, such as improved mechanical properties of LLDPE and good processability of LDPE. These blends could be classified into two categories or domains: LLDPE-richer blends and LDPE-richer blends. Blend composition ratio can shift towards each one of the domains depending on the availability of each resin in the market, the processing equipment, and the consumption habits of local market. As an example, the European market mainly produces LDPE-rich blends, while in North America dominates the use of LLDPE-rich blends.

A sustained LLDPE increase in blends has improved some attributes such as:

• Higher mechanical properties.
• Better appearance (transparency, gloss, lower gel level).
• Improved sealing properties.
• Lower production and transformation costs.

The benefits introduced by LLDPE have shifted market to use LLDPE-richer blends in applications such as: high performance bags, cushioning films, tire separator films, industrial liners, elastic films, ice bags, bags for supplemental packaging and garbage bags.

ADVANTAGES:

• Low cost
• Impact resistant from -40 C to 90 C
• Moisture resistance
• Good chemical resistance
• Food grades available
• Readily processed by all thermoplastic methods

DISADVANTAGES AND LIMITATIONS:

• High thermal expansion
• Poor weathering resistance
• Subject to stress cracking
• Difficult to bond
• Flammable
• Poor temperature capability

After its experimental preparation in the 1930s, the application in high frequency radar cables during World War II, gave impetus to its commercial production. This thermoplastic is available in a range of flexibilities depending on the production process. High density materials are the most rigid. The polymer can be formed by a wide variety of thermoplastic processing methods and is particularly useful where moisture resistance and low cost are required. Polyethylene is limited by a rather low temperature capability (200-250 F) but is manufactured in billions of pounds per year.
Vinyl acetate can be copolymerized with ethylene. The resulting product has improved transparency over homopolymerized polyethylene because of a reduction of crystallinity in the copolymer.

ADVANTAGES:

• Low cost
• Impact resistant from -40 C to 90 C
• Moisture resistance
• Good chemical resistance
• Food grades available
• Readily processed by all thermoplastic methods

After its experimental preparation in the 1930s, the application in high frequency radar cables during World War II, gave impetus to its commercial production. This thermoplastic is available in a range of flexibilities depending on the production process. High density materials are the most rigid. The polymer can be formed by a wide variety of thermoplastic processing methods and is particularly useful where moisture resistance and low cost are required. Polyethylene is limited by a rather low temperature capability (200-250 F) but is manufactured in billions of pounds per year.
Vinyl acetate can be copolymerized with ethylene. The resulting product has improved transparency over homopolymerized polyethylene because of a reduction of crystallinity in the copolymer.

ADVANTAGES:

• Low cost
• Impact resistant from -40 C to 90 C
• Moisture resistance
• Good chemical resistance
• Food grades available
• Readily processed by all thermoplastic methods

This polyolefin is readily formed by polymerizing propylene with suitable catalysts, generally aluminum alkyl and titanium tetrachloride. Polypropylene properties vary according to molecular weight, method of production, and the copolymers involved. Generally polypropylene has demonstrated certain advantages in improved strength, stiffness and higher temperature capability over polyethylene. Polypropylene has been very successfully applied to the forming of fibers due to its good specific strength which is why it is the single largest use of polypropylene. Polypropylene also happens to be one of the lightest plastics available with a density of 0.905 g/cm².

ADVANTAGES:

• Homopolymer
• Processability, Good
• Food Contact Acceptable
• Stiffness, Good
• Impact Resistance, Good
• Copolymer
• Flow, High
• Impact Resistance, High
• Chemically Coupled

DISADVANTAGES AND LIMITATIONS:

• Degraded by UV
• Flammable, but retarded grades available
• Attacked by chlorinated solvents and aromatics
• Difficult to bond
• Several metals accelerate oxidative degrading
• Low temperature impact strength is poor

TYPICAL APPLICATIONS:

• Automotive Applications
• Household Goods
• Film
• Containers
• Appliances
• Packaging
• Electrical/Electronic Applications
• Industrial Applications
• General Purpose

Unmodified polyvinylchloride is a very rigid thermoplastic. Flexibility can be increased over a wide range by adding varying amounts of several plasticizers such as dioctyl phthalate. A frequent method of processing PVC involves the suspension of solid particles of the polymer in an appropriate plasticizer. This suspension, a “plastisol,” is then heated resulting in a homogenous system which becomes a flexible solid upon cooling. Usage of PVC has grown steadily since its introduction in the early 1930s to become a very widely used plastic in a myriad of uses from films and mouldings to extruded pipe. PVC has excellent resistance to water and aqueous solutions, but it is attacked severely by stronger solvents such as aromatic hydrocarbons, ketones, esters and chlorinated solvents. Recently discovered health hazards due to extended exposure to the vinyl chloride monomer have resulted in strict production controls. Several alloys and copolymers are possible with PVC, including styrene and acrylonitrile. See also polyvinyl chloride/vinylidene chloride.

ADVANTAGES:

• Processed by thermoplastic methods
• Wide range of flexibility possible with varying levels of plasticizer
• Plastisol processing possible
• Non-flammable
• Dimensional stability
• Comparatively low cost
• Good resistance to weathering

DISADVANTAGES AND LIMITATIONS:

• Attacked by several solvent types
• Limited thermal capability
• Thermal decomposition evolves HCI
• Stained by sulphur compounds
• Higher density than many plastics

TYPICAL APPLICATIONS:

Pipe, extruded wire covering, toys, bottles, door and window components, film and fabric coatings.

Rotational Molding Uses:

Rotational molding, also known as rotomolding, is a thermoplastic molding process best suited for large, one-piece hollow parts and double-walled open containers such as tanks, kayaks, and coolers.

Rotomolding is often used for parts that require high-quality finishes, uniform wall thicknesses, and high stability. Features such as inserts and spin weld attachments can be incorporated directly into the rotomold and foaming can be used to create thermal insulation and stiffness. Unlike competitive processes such as blow molding and thermoforming, rotomolding produces no pinch-off seams or weld lines, resulting in a finished product without the use of secondary processes.

Advantages of Rotational Molding:

The main difference between rotational molding and competitive molding methods such as blow molding and thermoforming is that the resin melts into the mold walls instead of being forced by pressure. This distinction gives way to a number of advantages over other manufacturing processes, but also carries its share of drawbacks.

Advantages of Rotational Molding:

• Low-cost tooling: low operating pressures allow rotomold tooling to be crafted from low-cost metals such as aluminum
• Consistent wall thickness: the constant rotation of the mold coats the walls evenly during both the heating and cooling processes
• Double-wall construction: complex double-walled open containers can be produced without secondary processing
• High durability: parts are molded as one solid piece, eliminating the need for joining techniques such as welding and joint fabrication which creates weak spots
• High stability: the molding material isn’t exposed to external pressure, increasing its stability and reducing the risk of defects in the finished part
• High strength: rotomolding creates thicker corners, reducing the risk of failure in these stress-concentration points
• Appearance: the soft metal used for the rotomold tooling easily accommodates surface finishes such as fine-detail textures, logos, symbols, and lettering