Plastics Engineering Interview Questions and Answers
Question - 1 : - How Are Plastics Made?
Answer - 1 : -
Most commercial plastics encountered by consumers consist of building blocks of carbon. Those building blocks are typically derived from petroleum or natural gas, but can be derived from coal or biological sources. The building blocks of small molecules are called monomers. The monomers used are many and can be combined in various combinations to achieve special properties and characteristics.
The nature of the polymer science is such that the monomers must be very pure to make useful plastics. Plastics can be made at very high pressures using gases, in solvents or liquid emulsions, or as melted materials. Each plastic has preferred manufacturing techniques based on its specific chemistry. All successful chemical syntheses are characterized by purification of raw materials, reuse of surplus material, efficient conversion of materials to useful plastic, efficient use of energy, and minimized releases of byproducts to the environment.
Question - 2 : - Why Are Plastics Used In Packaging?
Answer - 2 : -
Packaging serves many purposes. The public may think the package lasts only a few minutes during the use of the product, but the real demands are much more extensive. Packaging must deliver the product through a potentially long distribution chain to the consumer such that the product meets all expectations regardless of the history encountered. The package must allow the product to be attractive and must deliver aesthetic appeal and information.
The package must protect the product at low cost and ease of use with minimal environmental impact. And the package must meet the various regulatory requirements set by various governments. With the proper selection of plastic and packaging type, the quality of the product good, ranging from sensitive electronics to fresh foods, can be maintained during shipping, handling and merchandising. Plastics are a versatile family of materials that are suitable for a wide range of packaging applications.
In many cases, plastics offer the best protection while using minimal resources and creating less waste than alternative materials. A study in Germany showed that 400 percent more material by weight would be needed to make packaging if there were no plastics, and the volume of packaging would more than double1. Another European study showed that if plastic packaging did not exist, the annual extra burden required to replace the packaging function would consume an additional 14.2 millions tons of oil (equal to a line of super tanker ships over 14 miles long) and produce an additional 47.3 million tons of CO2 (equal to the annual output of over 12 million automobiles)2. While all packaging continues to be optimized, the basic message of the efficiency of plastic packaging to deliver a product as expected and at low cost is still true.
Question - 3 : - Why Do We Need Different Kinds Of Plastics?
Answer - 3 : -
Copper, silver and aluminum are all metals, yet each has unique properties. We do not make a car out of silver or a beer can out of copper because the properties of these metals are not the best choice for final product. Likewise, while plastics are all related, each resin has attributes that make it best suited to a particular application. Plastics make this possible because as a material family they are so versatile.
For instance, six resins account for most of the plastics used in packaging:
- PET (polyethylene terephthalate) is a clear, tough polymer with exceptional gas and moisture barrier properties. PET’s ability to contain carbon dioxide (carbonation) makes it ideal for use in carbonated soft drink bottles.
- HDPE (high density polyethylene) is used in milk, juice and water containers in order to take advantage of its excellent protective water retention properties. Its chemical resistance properties also make it well suited for items such as containers for household chemicals and detergents. And HDPE is used for the secondary packaging, such as reusable pallets, that helps deliver products safely and efficiently in the product distribution system.
- Vinyl (polyvinyl chloride, or PVC) provides excellent clarity, puncture resistance, and cling. As a film, vinyl can breathe just the right amount, making it ideal for packaging fresh meats that require oxygen to ensure a bright red surface while maintaining an acceptable shelf life.
- LDPE (low density polyethylene) offers clarity and flexibility. It is used to make bottles that require extra flexibility. To take advantage of its strength and toughness in film form, it is used to produce grocery bags and garbage bags, shrink and stretch film, and coating for milk cartons.
- PP (polypropylene) has high tensile strength, making it ideal for use in caps and lids that have to hold tightly on to threaded openings. Because of its high melting point, polypropylene can be hot-filled with products designed to cool in bottles, including ketchup and syrup. It is also used for products that need to be incubated, such as yogurt.
- PS (polystyrene), in its crystalline form, is a colorless plastic that can be clear and hard. It can also be foamed to provide exceptional insulation properties. Foamed or expanded polystyrene (EPS) is used for products such as meat trays, egg cartons and coffee cups. EPS is also used for secondary packaging to protect appliances, electronics and other sensitive products during transport.
Question - 4 : - What About Cfcs Used In Plastics?
Answer - 4 : -
Chlorofluorocarbons (CFC’s) were used in the past to make foamed plastic. In response to concerns about the ozone layer, polystyrene manufacturers voluntarily phased out the use of CFC’s in the late 1980s.
Question - 5 : - Are Toxic Compounds Used To Make Plastics And If So, Would Not The Plastics Be Toxic?
Answer - 5 : -
Some of the raw materials used to make plastics are rather non-reactive at room temperature and others are highly reactive. For example, one reactive compound, ethylene, is used to make polyethylene. It can also be used to make waxes, such as paraffin wax used for candles and food additives. While not particularly toxic, gaseous ethylene is an asphyxiant, chemically active, and highly flammable. When converted to a plastic, those characteristics are changed. The plastics made from transformed raw materials do not have the same properties as the raw materials. EPA has concluded "there is an exceedingly low probability that potential exposure to high molecular weight water-insoluble polymers, as a class, will result in unreasonable risk or injury to human health or the environment".3Plastics molecules are very large and do not have the same biological properties as the raw materials used to make them.
Question - 6 : - Are Toxic Chemicals Included In The Plastic Products We Buy?
Answer - 6 : -
The simple answer is ‘not intentionally’. The more thorough answer is that toxicity is a complicated subject. Salt, and even water, at too high an intake are toxic to humans. Both are necessary for health and neither is considered toxic. To be a risk, any toxic material must be delivered to sensitive organs in sufficient quantity to create an adverse result. Health risk is not created by mere presence alone.
Plastic products may contain many additives that are included to change appearance, such as colors, or to change performance, such as materials that make stiff plastics more limp and flexible. All additives for food packaging must pass stringent testing to meet FDA requirements for indirect food additives whether the additive actually is ingested or not4. Additives for other than food packaging have other requirements to meet. In general, if an additive becomes identified as problematic, alternatives are found and used. As for the plastic itself, manufacturers recognize it is in their best long-term interest to be sure the plastic as made create negligible risk.
Question - 7 : - Why Are Plastics Used In Durable Goods?
Answer - 7 : -
Manufactured items defined with a useful life of more than three years, including automobiles, appliances, computers, etc., are called durable goods. Manufacturers of durable goods choose plastics for many reasons:
- The automotive industry chooses plastic for its durability, corrosion resistance, ease of coloring and finishing, resiliency, cost, energy efficiency, and light weight. Light weight translates directly into improved fuel usage experience and lowered costs to the consumer. Use of plastics in car bodies, along with improvements in coating technology, contribute to automobiles lasting much longer than vehicles did before the widespread use of plastics in fender liners, quarter panels, and other body parts.
- Major appliance manufacturers use plastics because of their ease of fabrication, wide range of design potential, and thermal, electrical, and acoustic insulation. Plastics characteristics can significantly reduce production and use energy consumption and greenhouse gas generation. Plastic insulation in refrigerators and freezers helps reduce operations costs to the consumer.
- The building and construction industry uses vinyl siding for homes because of its appearance, durability, ease of installation, cost, and energy efficiency.
- Plastics can reduce energy consumption for the auto, appliance, and building and construction industries, providing a substantial saving in production costs.
Question - 8 : - What Is Plastic Film?
Answer - 8 : -
Stretchy plastic items such as carrier bags, bubble wrap, vegetable and food bags, cling film, crisp packets, magazine wrappers etc are all types of plastic film. Please refer to this plastic film leaflet which lists items that can and can’t be recycled in the red plastic and cans recycling box.
Question - 9 : - Why Won’t You Collect Plastic Film For Recycling Anymore?
Answer - 9 : -
There are limited outlets to sell plastic film and sorting it from plastic bottles, pots, tubs and trays is very costly. Removal of film from our recycling will assist in maximising the council’s income from all material collected thus reducing costs to the council tax payer in these difficult financial times.
Question - 10 : - Why Have I Not Been Told?
Answer - 10 : -
The change to Powys’ plastics and cans kerbside collection service has been communicated publically via press releases published in the local newspapers, advertising on the Powys County Council website and campaigns using social media online in the last few weeks. Full details were also included in the literature for the three weekly refuse collection service which were delivered to every household in Powys.