Closely analyzing the exhibit, it can be seen that grade 612 has the best modulus and thus stiffness as well as creep property. However, it has moderate heat deflection temperature of 180 degree C, therefore having lower resistance to creep at higher temperatures.
Grade 46 has the best impact property. However, it has the tendency to absorb moisture at high levels. All polyamides tend to have an adverse impact on impact property at higher moisture contents. High impact of grade 46 tends to get reduced because of its affinity for moisture.
PA grade 6,6 has a good balance of strength, stiffness, heat resistance, resistance to hydrocarbons, lubricity and wear resistance. PA 6 has a better creep resistance but lower modulus than PA 6,6; it processes at lower temperatures than 6,6 and with less mold shrinkage. It also gives a lustrous surface, which is useful where appearance is a concern. However, it absorbs moisture more readily than grade 6,6.
PA 4,6 has among the highest impact strengths of commercial grades of nylon, but its modulus is less than that of PA 6,6 Grade 4,6 has excellent resistance to wear and friction, and has outstanding flow characteristics, which makes it easy to process. However, the 4,6 material has a relatively high moisture absorption.
Compared to other grades, PA 12 has a relatively low concentration of amide groups in the polymer chain, which gives it the lowest water absorption of any commercial grade. It also has good to excellent resistance to oils, fuels, hydraulic fluids, solvents and salt. The material also resists stress cracking and abrasion.
PA 6,12 is also fairly low in moisture absorption and has many properties similar to grade 12. However, compared to grade 12, the 6,12 polymer has a higher heat deflection temperature, and greater tensile and flexural strength.
Polyamide 11 is also relatively low in moisture absorption. It features a high degree of chemical resistance and the ability to accept high loadings of fillers. However, relative to other types of PA, grade 11 is higher in cost and less heat resistant.
Polyamide 6,6 is the most popular form of nylon, followed by PA 6.
Automobile applications
Automobile air intake manifolds were once made of metal, but today are often fabricated from 30-35% glass-reinforced PA 6. Grades 6,6 and 4,6 are also used in manifolds. Substituting metal in the manifolds with nylon reduces production costs by up to 30%, reduces the weight of the part by up to 50%, cuts system costs through parts integration and contributes to higher fuel efficiency.
PA 4,6 is occasionally used for air intake manifolds, especially where a manifold is exposed to temperatures that exceed the capabilities of PA 6 and PA 6,6. Higher cost of PA 4,6 compared to 6 and 6,6 restrict its usage to some extent.
Engine covers are another frequent application of PA 6. Compared to other types of nylon, the high-flow grades of PA 6 are more suited for this application because it allows thinner walled designs, a better surface appearance, and a wider processing window due to better flow and lower injection pressures. Rocker valve covers are another place where PA 6 is increasingly found in automobile. For this application, PA 6 maintains strength and stiffness better over the life of the vehicle than PA 6.
In airbag containers, PA 6 offers parts integration and reduced weight compared to metal containers. Containers made of PA 6 do not splinter at low temperatures, as do some other polymers. It also possesses sufficient stiffness and strength to withstand high temperatures without failure.
For a car's powertrain, manufacturers are promoting plastic chain tensioner guides made of PA 4,6. One reason is that it offers better wear performance than high molecular weight PA 6,6, and PA 6,6 It also enhances safety and reduces noise generation. PA 6,6 has found its way into automotive cooling systems, where it allows consolidation of various components once made of aluminum and plastics. PA 6,6 is also used in headlamp bezels.
PA 6 also is being deployed in exterior automotive parts. These include door and tailgate handles, exterior mirrors, front-end grilles, fuel caps and lids, and wheel covers and trim.
Elsewhere in the automotive world, PA 12 is used in fuel lines, while PA 6,12 is found in hydraulic clutch lines.
Electronic applications
PA 6,6 has long been a material of choice in electronic connectors. However, it is giving way to PA 4,6 in this application because connectors are increasingly exposed to high temperatures. This is especially the case as lead-free soldering continues to advance in the industry. These high temperature soldering operations require connector materials that are stable to at least 230° C. Today's connectors have higher pin counts than in the past, requiring improved weld-line strength and better flow.
There is also a finer pitch between pins, which necessitates connector materials with high flow, high mechanical strength, and exceptional weld-line strength. In many cases, PA 4,6 meets all these requirements.
PA filled with electrically conductive materials can provide antistatic, electrostatic discharge (ESD) and EMI/RFI shielding for electronic equipment, as well as for trays and conveyer systems used in the manufacture of semiconductor chips. Common fillers in this application include carbon fiber, carbon powder, nickel-coated carbon fiber, and stainless steel fiber. Just about any grade of PA can be used in ESD and EMI/RFI protection.
Packaging applications
I n food packaging, PA 6 films provide excellent barrier properties that keep oxygen out and seal aroma in. The films can be made by cast, blown or biaxially oriented polyamide(BOPA) processes. Foods commonly packaged with PA 6 resin includes meats, cheeses, dried foods, and chilled fruit juices. Oxygen permeability of the nylon films increases with temperature and humidity.
Consumer packaging made of PA 6 provides a good combination of strength, tear and puncture resistance. An example of this packaging is air cellular cushioning, which protects products from damage during shipment. In the medical field, PA 6 is fabricated into tough, puncture-resistant packages for medical blister packs.
Nano composites based on PA 6 are also being developed for packaging applications. In these cases, the polymer is loaded with 2-8% of an organically treated mica-like clay mineral that is dispersed throughout the polymer in micron-size particles. Film or sheet made of the nylon nano composites display a fourfold improvement in oxygen barrier properties over unfilled PA 6 film. Compared to the unfilled nylon, the nylon nano composite also exhibit a 35° C improvement in heat deflection temperature, more than a third greater tensile strength, and a 50% improvement in flexural modulus. Recommended packaging applications of the nano composites include foods, cosmetics, medical products and electronic equipment |