Chem 9 Lab: Synthesis Experiment

1 Name: Chem 9, Section: Lab Partner: Experiment Date: Synthetic Polymers and Plastics Part A

Find or choose one type of each of the following plastic polymers, and report the following characteristics: Plastic number, Short Name, Clear (yes or no), Opaque (yes or no), Flexibility (can be bent?), Durability (hard or soft), Breakability (can be cracked?), Recyclable (yes or no).

Report for plastic samples in each liquid: sinks rapidly, sinks slowly, floats on top, floats below surface. Given the densities for ethanol/water (0.94 g/cm3), water (1.0 g/cm3), and 10% NaCl solution (1.08 g/cm3), determine the relative densities of each plastic sample and rank them from lowest to highest density.

Polymer Ball composition, approximate height bounced, and physical characteristics for three balls. Answer questions regarding the most flexible of the Big Six plastics, suitable materials for specific applications, the density range and composition of a floating plastic, importance of dislodging bubbles in density tests, separation of PET from waste plastics, effects of mixing HDPE and PVC, reasons for careful polymer identification, details about polymerization of PS, structure of PVC polymer, the monomer involved in making the bouncy balls, role of ingredients like glue, borax, cornstarch, and the comparative bounce heights to infer which compound influences bounce most.

Paper For Above instruction

Introduction

Understanding synthetic polymers and plastics is fundamental to materials science, as these materials significantly influence modern manufacturing and environmental management. This study aims to investigate the physical characteristics, density behaviors, and applications of different plastics, with particular attention to environmental implications and polymer chemistry. By examining the properties of selected plastics, analyzing their buoyancy in various liquids, and exploring the fabrication of polymer-based bouncy balls, the research provides insights into polymer characteristics relevant to recycling, utilization, and environmental impact.

Part A: Physical Characteristics of Selected Plastics

In this section, one type each of the major plastics classified under the Plastic Identification Code (PIC) system was chosen for examination. The selected plastics include high-density polyethylene (HDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). Each plastic exhibits distinct physical features that influence its application and recyclability.

HDPE, characterized by its high strength-to-density ratio, is opaque, flexible, and durable but can be cracked under stress, and is recyclable. Conversely, PET, commonly used for beverage bottles, is transparent, rigid, and recyclable but less flexible. PVC is rigid or flexible depending on plasticizer content, opaque, and recyclable. LDPE is translucent or opaque, highly flexible, and soft, making it ideal for bags, yet less durable. PP offers a balance of stiffness and flexibility, suitable for containers and fibers, and is recyclable.

Part B: Density Tests and Buoyancy Analysis

The density test involved immersing plastic samples in ethanol/water (0.94 g/cm3), water (1.0 g/cm3), and NaCl solution (1.08 g/cm3). The observed behaviors—sinking rapidly, sinking slowly, floating on top, or floating below—allowed determination of relative densities (1). For instance, plastics that sank in ethanol but floated in water have densities between 0.94 and 1.0 g/cm3, indicating materials like LDPE or PP. Those sinking in NaCl solution but floating in water have densities between 1.0 and 1.08 g/cm3, suggesting higher-density plastics such as PET or PVC. Ranking these densities from lowest to highest provides insight into their buoyancy in various environments, which is crucial for recycling processes and environmental assessments.

Part C: Polymer Bouncy Balls and Polymer Chemistry

The polymer balls were fabricated using specific monomers and cross-linking agents like glue, borax, and cornstarch. The monomer for the bouncy balls is typically styrene, which polymerizes through free-radical mechanisms to form polystyrene. The role of each additive is to facilitate cross-linking (borax in polyvinyl alcohol-based glues for elastic properties), act as a binder (cornstarch as a filler), or modify properties for elasticity and bounce.

The bounce height indicative of polymer elasticity varies among the balls. The ball with the highest bounce likely contains polybutadiene or a highly elastic polymer network. The structural analysis of monomers and polymerization mechanisms shows that styrene and butadiene contribute significantly to the elasticity and rebound capacity of the balls.

Environmental and Practical Implications

The separation of PET from other plastics is essential for effective recycling. Commercial methods such as density separation, using float-sink tanks, can selectively recover PET due to its density difference. Mixing polymers like HDPE and PVC can alter the buoyant properties observed in density tests, complicating sorting processes.

Accurate identification of polymers is vital for recyclers to prevent contamination, which can impair the recycling process and the quality of recycled products. Scientists and industry professionals employ spectroscopic techniques such as Fourier-transform infrared spectroscopy (FTIR) and near-infrared (NIR) analysis for precise polymer identification.

The polymerization of polystyrene involves the link of monostyrene units through a head-to-tail arrangement, creating a linear polymer chain with repeating styrene units. Polyvinyl chloride (PVC) is synthesized by free-radical polymerization of vinyl chloride monomers, forming a polymer with a backbone of carbon atoms with pendant chloride groups, which influence its rigidity and chemical resistance.

In the context of the bouncy balls, styrene monomers polymerize to form polystyrene, with the bouncing ability enhanced by the flexibility conferred through cross-linking agents like borax and the inclusion of fillers such as cornstarch. Among the ingredients, borax forms reversible cross-links with polyvinyl alcohol, increasing elasticity and resilience, thus contributing to the bounce.

Conclusion

The study highlights the importance of understanding the physical and chemical properties of plastics, their buoyancy behaviors, and the implications for recycling and environmental health. Accurate identification and separation of polymers ensure sustainable management of plastic waste, reduce environmental pollution, and advance the development of recyclable materials with desirable physical characteristics like flexibility and durability. The polymer chemistry underlying the fabrication of bouncy balls exemplifies practical applications of monomer knowledge and cross-linking techniques in creating elastic, resilient polymer products.

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