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Chapter 14: Problem 14

(a) Is it possible to grind up and reuse phenol-formaldehyde? Why or why not? (b) Is it possible to grind up and reuse polypropylene? Why or why not?

Short Answer

Expert verified
Answer: Phenol-formaldehyde cannot be ground up and reused due to its thermosetting nature and cross-linked structure. On the other hand, polypropylene can be ground up and reused because it is a thermoplastic with long linear chains that can be re-melted and re-molded multiple times without undergoing any chemical change.

Step by step solution

01

(a) Phenol-formaldehyde: Thermosetting or Thermoplastic?

One crucial aspect to consider while determining the recyclability of a plastic is whether it is a thermosetting plastic or a thermoplastic. Thermosetting plastics are the ones that undergo a chemical change when they are heated and set, and thermoplastics are the ones which can be heated and molded multiple times without undergoing any chemical change. Phenol-formaldehyde is a thermosetting plastic, which means that its chemical structure changes when it is heated and molded. As a result, it cannot be re-melted and re-molded once it has been set.
02

Phenol-formaldehyde: Chemical structure and cross-linking

The chemical structure of phenol-formaldehyde consists of phenol and formaldehyde molecules bonded together in a cross-linked network. This cross-linking is what provides phenol-formaldehyde with its strong, rigid, and heat-resistant properties. However, this cross-linking also means that the material becomes highly inflexible and cannot be reprocessed once set. Breaking the cross-linked bonds would require an excessively high amount of energy, which would most likely lead to the degradation of the material.
03

(a) Conclusion: Can phenol-formaldehyde be ground up and reused?

Considering the chemical structure and properties of phenol-formaldehyde, it is not possible to grind it up and reuse it. The thermosetting nature and cross-linking of the material render it non-recyclable.
04

(b) Polypropylene: Thermosetting or Thermoplastic?

As in the case of phenol-formaldehyde, we need to determine whether polypropylene is a thermosetting plastic or a thermoplastic. Polypropylene is a thermoplastic, which means that it can be heated and re-molded multiple times without undergoing any chemical change.
05

Polypropylene: Chemical structure and properties

The chemical structure of polypropylene consists of long, linear chains of propylene monomers bonded together. These chains can be heated and melted and retain their properties upon cooling and solidification. This feature makes polypropylene highly amenable to recycling processes. Additionally, polypropylene has excellent chemical resistance and good processability, which contribute to its widespread use in various applications like packaging, automotive components, and consumer products.
06

(b) Conclusion: Can polypropylene be ground up and reused?

Given its thermoplastic nature and chemical structure, polypropylene can be ground up and reused. Recyclers can collect, clean, and reprocess polypropylene waste into new products with similar properties and uses. This makes polypropylene a more environmentally friendly and sustainable choice compared to non-recyclable thermosetting plastics like phenol-formaldehyde.

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Most popular questions from this chapter

Sketch the repeat structure for each of the following alternating copolymers: (a) poly (butadiene-chloroprene), (b) poly(styrene-methyl methacrylate), and (c) poly(acrylonitrilevinyl chloride).

The following table lists molecular weight data for a polypropylene material. Compute (a) the number-average molecular weight, (b) the weight-average molecular weight, and (c) the degree of polymerization. \begin{tabular}{rcc} \hline Molecular Weight Range \((\mathrm{g} /\) mol \()\) & \(\boldsymbol{x}_{\boldsymbol{i}}\) & \(\boldsymbol{w}_{\boldsymbol{i}}\) \\ \hline \(8,000-16,000\) & \(0.05\) & \(0.02\) \\ \(16,000-24,000\) & \(0.16\) & \(0.10\) \\ \(24,000-32,000\) & \(0.24\) & \(0.20\) \\ \(32,000-40,000\) & \(0.28\) & \(0.30\) \\ \(40,000-48,000\) & \(0.20\) & \(0.27\) \\ \(48,000-56,000\) & \(0.07\) & \(0.11\) \\ \hline \end{tabular}

High-density polyethylene may be chlorinated by inducing the random substitution of chlorine atoms for hydrogen. (a) Determine the concentration of \(\mathrm{Cl}\) (in wt \(\%\) ) that must be added if this substitution occurs for \(5 \%\) of all the original hydrogen atoms. (b) In what ways does this chlorinated polyethylene differ from poly(vinyl chloride)?

Calculate the number-average molecular weight of a random nitrile rubber [poly (acrylonitrile-butadiene) copolymer] in which the fraction of butadiene repeat units is \(0.30\) assume that this concentration corresponds to a degree of polymerization of 2000 .

Explain briefly why the tendency of a polymer to crystallize decreases with increasing molecular weight.
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