⚡ Polypropylene Advantages And Disadvantages

Monday, August 09, 2021 11:37:19 PM

Polypropylene Advantages And Disadvantages

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Polypropylene (7a)

One way to control the molecular weight of high-density polyethylene created is through chain transfer reagents. Some typical chain transfer reactions are shown below:. This reaction leaves aluminum bound to the polymer chain. Exposure to moisture hydrolyzes the bond. The reaction most important to controlling the molecular weight of high-density polyethylene created by the Ziegler Process is chain transfer with the introduction of hydrogen. A brief description of the Ziegler process will be explained in the following paragraph. First, the organometallic compound i.

The pressure of the reaction vessel is between atmospheric and 20 atm. Ethylene is introduced into the reactor vessel in the gas phase. The boiling point of ethylene is approximately — degrees Celsius. The ethylene reacts with the active site of the catalyst to produce polyethylene. The solvent is used to dissipate heat. The solvent must not vaporize or react with any of the compounds in the reactor inert solvent. The melting point of high-density polyethylene is approximately degrees Celsius. Therefore, the polyethylene formed is in the solid phase. This type of polymerization is called slurry polymerization or suspension polymerization. The slurry solution is passed to a catalyst decomposition bed where the catalyst is deactivated.

The catalyst is not completely used in the polymerization process. Catalyst decomposition is achieved with the addition of an alcohol. Polyethylene is then recovered with the extraction of the solvent, and a filtration and drying process. The polyethylene can then be processed and manufactured. The polyethylene created by the Ziegler process has a molecular weight 20, and 1. The Ziegler process produced a high-density polyethylene at pressures as low as atmospheric pressure.

High-density polyethylene is a more durable polymer when compared to low-density polyethylene due to its lower degree of branching. The Phillips process is very similar to the Ziegler Process. The Phillips Process, the process commercialized by Phillips Petroleum Corporation in , uses a catalyst to create an active site for polymerization. Historically, this was the first method used for commercial ethylene polymerization with the original Ziegler catalyst. At present, Phillips Petroleum utilizes a highly active catalyst, chromium oxide on a high-surface area silica, to produce high-density polyethylene.

The active site for polymerization, Cr-C bond, is achieved by reacting the catalyst with an olefin. The olefin reduces the valence state of the transition-metal atoms, thus, making it more reactive. The reaction mechanism is similar to the mechanism explained for the Zeigler process. The first generation Ziegler catalysts were not very active and had to be removed through a complex extraction process. An alcohol was added to deactivate the catalyst. Many of the polymer processes had in front of the main reactor a special reactor in which the catalyst preparation took place and the viscosity, morphology, control was a very important step.

The use of a silica base eliminates this problem. The catalyst is very active and it no longer needs to be removed because all of the catalyst is reacted with the monomer ethylene. The active sites on the monomer are equally accessible to the monomer throughout the particle. Therefore, the polymer chains grow not only outwards but also inwards, causing the granule to expand progressively.

The polymer particle will be a replica of the catalyst particle if the mechanical strength of the particle is high enough. Because of the complexity and importance of the silica base catalyst, the catalyst is often prepared in a separate production plant. The Phillips process is shown below:. A brief explanation of the Phillips process is provided in the following paragraph. The process shown above represents Phillips Petroleum Co. The polymer particles are suspended in an inert hydrocarbon. If the polymerization were to take place at a temperature greater than its melting temperature then the polymer formed would be in the liquid phase.

A loop reactor is used in a liquid-phase process. The catalyst and the inert solvent are introduced into the loop reactor where ethylene and an a -olefin are circulating. The inert solvent is used to dissipate heat as the reaction is highly exothermic. A cooling jacket is also used to dissipate heat. The active sites on the catalyst are equally accessible to the monomer throughout the particle.

The reactor consists of a folded loop containing four long runs of pipe 1 m in diameter, connected by short horizontal lengths of 5m. The reason for the high velocity is because at lower velocities the slurry will deposit on the walls of the reactor causing fouling. Ethylene, alpha olefin comonomer if used , an inert solvent, and catalyst components are continuously charged into the reactor at a total pressure of psig.

The pressure is a lot higher than the pressure used to create high-density polyethylene by the Ziegler process. The HDPE created by the Phillips process typically has one ethyl branch per every molecule chains while HDPE created by the Ziegler process has three ethyl branches per every molecule chains. Because of this, the density of high-density polyethylene created by the Phillips process is higher.

This has its advantages in processing. The HDPE created by the Phillips process is more crystalline and it is used to create more durable products. The solvent is recovered by hot flashing. Teddy Bears. Name Badges. Exhibition Bags. Trade Show Giveaways. Wristbands Silicone Wristbands. Desk Accessories. Made In UK. Individually Named Items. Executive Products. Shop By Season Christmas Easter. Best Sellers - Top New Products - Brand Extension — Advantages and Disadvantages. Examples of successful brand extensions Brand extensions can either be a total success or a complete failure. These are just some of the cases when they were successful: Wipro — the brand was originally geared towards computers, but has since extended into soaps, powders, and shampoos.

Mars — today, we have not only Mars chocolate bars but also Mars ice cream, Mars chocolate drinks and many more extensions of the original product. Rasna Ltd. Advantages and disadvantages of brand extension Advantages: They can help the product be easily accepted. They can also improve the overall brand image. Since the company has established the brand name as trustworthy and popular, they can also increase the interest of consumers and make them consider a new product.

That also leads to better distribution. Companies spend less money on promotional expenditure, or the money is better used. By promoting the core brand, companies are also promoting the extension. The same goes if they are promoting the extension — the core brand will gain recognition as well. Consumers get more variety than before. Packaging and labelling are more efficient, as the machines can print out the same labels and packages. Less money spent on introductory and follow-up marketing programmes.

Feedback benefits, both for the parent brand and the company itself. The parent brand gets a better image. Brand extensions help revive the brand. One brand extension allows for more extensions in the future. The extensions clarify what the brand stands for. They attract new customers, as the brand expands on the market. The core brand is an association for the new product. Thus, if the core brand is also associated with quality, the new product will be too. Disadvantages: Extending the brand name too far may lead to a loss of reliability, especially if the brand extension happens in an unrelated market.

Thus, companies have to know which product categories will work and where they can actually use the brand name. As the founder of GoPromotional, with over 25 years of expertise, Gareth has developed an enviable industry reputation.

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