1 Polymers SRINVAZ SSOOOT Tz 3 Ta) ei cera oed + How are addition and ee eed Couey Seer of plastics affect our environment? STU recycled and what are eee nck Deemed eae Have you seen the spectacular waterfall at Jewel Changi Airport? The Rain Vortex is the world’ tallest indoor waterfall, with water flowing down 40 metres. The water is enclosed within an acrylic funnel Chemistry Connect Launch ths resource to id out bat Acrylic isa transparent and strong plastic. Its commonly used designe pobmersae to make aquariums and windows of submarines. What other objects are made of acrylic? Much of the plastic is thrown away after use. This has a negative impact on our environment. In this chapter, we will find out how plastics are formed and used. We will lso consider the implications of disposing of and. recycling plastics. 381Chapter 21" polymers 21.1 What Are Polymers? Learning Outcome + Describe polymers a: large molecules built up from small units (monomers), and different polymers having diferent units and/or different linkages. ‘Many things around us are made from polymers. For example, the chair we sit on and the bedding we use are made from polymers (Figure 21.1). —_ ona, ‘some polymers can be obtained from natural sources. Other polymers such as acrylic are | See ee eS. ear polymers. Table 27.1 Different types of polymers fase Parees | Spaintstieen | no a wont oe " oie ca since‘Chemistry in a Sustainable World © Chapter 21 Wool silk. nyion and Terylene are commonly used to make clothing. ‘Natural nibber is used to make tyies and other objects that require high strength and flexibility. Polyvinyl chloride (PVC) is easily shaped and widely used as parts of machines, veicles and household appliances (Figure 21.2). Can you spot things around you that are made from these polymers? What smarts an ciferences do you observe between these polymers? Polymers are large organic molecules containing thousands or millions of atoms. They are formed when many small molecules join together. These small molecules are called monomers. Different polymers are made up of, Figura 2712 different monomers. they can also contain different linkages. You willlean PVC canbe used about these linkages later in this chapter. to make pipes polymer isa very large organic molecule built up from many small units alled monamers ‘The process of joining together a large number of monomers to form a polymer is called polymerisation (Figure 21.3).The monomers in a polymer ate joined together by covalent bonds. ‘Figura 23.2 Plymerisation Let's Practise 21.1 1 Exphin whats meant by each ofthe following terms: {@) monomer (©) _pohmer 2 What type of bonds are formed during polymerisation? Past to Present [Naural rubber can be obiained from ruber tres inthe form of ae. Latex isa wht, sticky substance that ‘comes from therubber te, Rubber ree are native to South America, tn the 10h century, he demand for rubber increased grelly du wo the invention of adomobiles. “With ths increasein demand, scientists experimented o find a substitute for natural rubber. The rubber -substute needed to have smilr propertes tortura rubber. and the manufacturing cos’ had tobe ow nally scientists creatvay and delerminaton led tthe development of syathetic ruber Large sale production of synthetic rubber started actoris fom 1910. Hewever, the quality the synthetic ‘Figure 214 rubber waslow. Iwas ony int: 1940s hat scicaliss, supported by governments and companic, found good eae ‘and cos fective ways to mak syelc rubber. Today, scents continue lo conduct experimen o make diferent types of synthetic rubber (Figure 21.4) that have properties of natural rubber. sensChapter 21! Polymers 21.2 How Are Addition Polymers Formed and Used? Leaning Outcomes + Descibe the formation of pely(ethene) as an example of ation pelymenation of ethene 25 the monomer. + State some uses of polythene) asa typical plastic. + Deduce the structure ofthe addition polymor product from a given monomer and vice vera, Plastic bags used to contain groceries are a common sight at supermarkets in Singapore. “The type of polymer used to make such bags is polyethene) Figure 21.5. Figure 21. Pelyethene) bagearewideyusadin Figure 21.6 Abani model showing acaton of ply thene) cour dally fives Recall for Chapter 19: “Adkenes undergo addition reactions such as adion Poly(ethene) has very large molecular mass. There can be thousands of carbon atoms in ‘each poly(ethene) molecule (Figure 21.6). Why Is this so? What property makes poly(ethene) suitable for making things such as plastic bags? Addition Polymerisation ‘When monomers join together without losing any molecules or atoms the polymer formed is ‘alled an addition polymer. This process i called addition polymerisation. > Addition polymerisation 9 nylon 6 ‘Answer u ° ‘Theropeat unt of nylon-6 a Ne (CH), a Ce‘Chemistry in a Sustainable World © Chapter 21 Tech Connect ew ‘To med the sharp increas in demand for some polymer based products, cenit and engincers experiment with diffrent ways to mak the products, ‘This is made casir with the advancement of technology. _Durng the COVID-18 pandemic. due tothe high demand for testing Ks. Singapore basod company colaberted with other companies, universities and ‘matical institutions across Singapore te produce lage numberof naa esting peaks (Figure 21.26). They produced the swabs using three-dimensonal (3D) printing technology [AD printer is simiar toa normal pete, Powever. instead of nk. polymers are steed 26 the printing materia When 30 digital mod ent othe 3D printer Figure 21.26 Anasaltesting sabi ‘ia compar, the printer pats layers of material together o form the 3D ebject ‘used to tetfor the COVD 19 vires (@igue2127). Floure 21.27 A3D printer uses polymers fr printing. Besides medical products, 3D printing can be ute to manulacure variety of objects. Wha! are the advantages cf'3D printing? ‘What would youmakeif you fad a 2D printer? Let's Practise 21.3 1 (a), Draw the structure of Teryiene, showing two fepeat units {b)_ Name the type of linkage found in Terylene. Link 2 List two usas of nylon. sdk ‘worker 21 395Chapter 21 © Polymers 21.4 How Does the Disposal of Plastics Affect Our Environment? Learning Outcome | Describe the pollution problems caused by the disposal of non-blodagradable plastic. Increasingly, plastics are boing used in place of natural materials such as wood, metal cotton, and leather because they are: + relatively cheap; ~ easily moulded into various shapes; + light, tough and waterproof; and + durable (resistant to decay, rusting and chemical attack). However, most plastics are non-bledegradable. This means that they cannot be broken ‘down by bacteria and other living organisms in the soil. Hence, the biagest problem with ‘the use of plastics s how to dispose of them after they are used or no longer required. Figure 21.28 shows the environmental problems caused by the disposal of non-biodegradable plastics, Biology at pontion potion pottton Paste donot dcompose.hus, Past! noantothe sea Pdcsae ost fanmabie cart png ad Barjing plc wasn nis) endanger arneanimas for When plates ae nerfed, sme of nan lesb ogniceninganoutot exampe-tutescln make they pote obowcis e- ximstpneced'o | Santap wate plat tayrtortootsratene Far eampe WC proaics ae ontem Corosve agen lord gason a Pastksmayabedogup anes conbston. dara nich mgt become bree ound or mosques. Figure 21.28 fects of deposal of plastic onthe erronment Let's Practise 21.4 + Explain what is meant bythe term non-biodegrodable. +2 Plastic waste can be disposed of by burning iin an incinerator. Give one advantage and one disadvantage of this method.‘Chemistry in Sustainable World "© Chapter 27 21.5 How Are Plastics Recycled ELAR ue ete Cry Related to Recycling Plastics? Learning Outcomes + Describe two methods of recycling plastics a: = the physical method (exemplified by melting small places of polythene) waste into pallets and ~ the chemical method (exemplified by depolymeriation and cracking of plastic waste into chemical feedstock and fuel respectively) + Desctibe depolymerisation 2s 2 process in which polymers are broken ‘down into their monomers, exemplified by hydrolysis of polyesters sing acid, + Discuss the socal, economic and environmental issues of recycling plastics Recycling bins are commonly seen in Singapore (Figure 21.29). Do you know how to make proper use of them? How are plastics recycled and what are the issues involved? 397Chapter 21" polymers Ghemistry Connect ‘ane his resource to find oat wit happens in recyeling plat Link Recall fom Chapter 18: ‘Cracking canbe wed to ‘break down long chain Iydrocrbons into smaller molecules, Recycling Plastics Recycling of plastics can be carried out using the physical method or the chemical method. Before recycling is carried out, te plastic waste necds to undergo ro treatment. This because not all plastics can be recycled. The recycling method for different types of plastic canbe diferent Pre-treatment of plastic waste involves: + sorting by difierant methods (e.g. manual sorting, sorting by donsity); ‘+ washing to remove contaminants; and | shradding or grinding to smaller pieces. Physical Method “The physical method of recycing plastics Is also known as mechanical recycling, Using this ‘method, the chemical composition ofthe recycled plastic remains unchanged. After pre-treatment, small pieces of plastics such as poly(ethene) are melted, cooled, pallad int long, thin strands, and cut into pellets (Figure 21.30), ‘These pellets can ‘then be made into new products Figure 21.30 Plastic pellets obtained from the physical method of recycling Chemical Method ‘The chemical method of recycling plastics converts plastic waste into different raw materials ‘through different chemical reactions. rach Plastic waste, such a palyfthene) waste, can undergo cracking to form short chains of «alkanes and alkenes The short-chain akanes can be used a uel hie the short-chain Skanes can be used to make other usefl chemicals. Cracking requites 3 hightemperature and the presence ofa cata. Depolymertsation ‘Apolymer can be converted back int its monomers. This process isknown a5, ‘depolymerisation, After depolymerisation, the monomars can be converted to other useful chemicals. Depolymerization sa process in which polymers are broken down into their monomers. Polyesters can undergo depolymerisation through acid hydrolysis. This involves breaking ‘down a polyester using water in the presence of an acid catalyst (Figure 21.31). The products are the monomers used to form the polyesters —a dicarboxylic acid and a diol. Ca) He 2 #2010 > n Hw Ow Cale CeOnH + 9 Ha Oath Ont oo Cae Cu One Figure 21.31 Red hydrolyss ofa potyester‘Chemistry in a Sustainable World © Chapter 21 Polyethylene terephthalate (PET) Isa polyester commonly used to make plastic bottles (Figure 21.32). Both the physical and chemical methods can chomicl method ‘Figura 21.23 How PET canbe recycled Issues Related to Recycling Plastics {tis very important to minimise pollution caused by the disposal of plastic waste. There are different ways to minimise plastic waste. We can fist reduce the plastics we use, and reuse plastics forthe same or new purpose. \freducing and reusing are not possible, we should recycle the plastic ‘object instead of throwing i anay. In 2019, only 4% of plastic waste generated by Singapore households was recycled. What are some issues related to the recycling of plastics? Environmental Issues of Recycling Plastics ath the physical anc chemical methodk of recycling plastics may lead ‘0 environmental issues. For example, if wastewater generated from the recycling process is not treated properly before being discharged Into water bodies it can contaminate the water and cause water pollution. Economic Issues of Recycling Plastics Recycling plastic waste can be ex costing much more than disposal in landfill: fr incineration, + There isthe cost of transporting the waste to the processing plant. + There are also the costs of sorting and F ‘deaning the waste, and carrying out either physical or chemical recycling processes. + Allthe processes involved in recycling plastic waste require manpower, machines ter and energy (Figure 21.34) ‘tmay not be worthwhile or economically viable to recycle plastics {the costof recycling plastic waste Is higher than the value of the recycled plastics. «Recycled plastics usually have 2 lower market value than vighn plastic that are made from raw materials and not obtained from recyling processes. This means that they ae sold at loner value ‘an virgn plastics. + ttl be cficult for recycling businesses to survive ifthe cost of recycling plastic wastes too high. 399Chapter 21 Polymers Social Issuas of Recycling Plastics In Singapore, many people find it more convenient to throw all their waste away. ‘As a result, recyclable plastics are disposed of and are not recycled. 2. Many people are not aware ofthe proper way to recycle plastics. When recycling is nat ‘aried out propery plastic wast in recycling bins may not eventually get recycled. ~ When recyclable items such a plastic containers are contaminated with leftover food, the recyclables usually end up being incinerated and not recycled. + Non-tecydable items, including some types of plastic, are sometimes thrown into recycling bins This incieases the time and effort to separate recycables from the wast, and slows down the recycling process. 3. Itakes time and effort for communities to adopt recycling 2s a lifestyle, so it might not be immediately effective. How can we help to address the issues related to recycling plastics? + Strict measures and laws must be putin place to minimise potential environmental sues. + Recycling programs can be introduced to educate the public on the correct way to recycle plastic waste. “+ Creative activties can be introduced to encourage people to practise recycling. For example, smart Reverse Vending Machines that are able to identify, sort and collect ‘empty plastic bottles are located throughout Singapore (Figure 2135). When anumber ‘of plastic bottles is deposited in the machines, users ae rewarded with bonefits such as discount coupons. Everyone can contribute to the recycling of plastics. How would you ‘encourage your family and friends to recycle plastic waste? Figure 21.85 Reeyeling a plesticbotil using «smart Reverse ending MachineLet's Practise 21.5 1 Describe the physical method of recycling plastics, starting from the pre-treatment process. 2 Explain why depolymerisation can help to reduce pollution caused by plastic vaste +3 List two social issues related to recycling plastic waste. (©) Problem-based Learning Activity Imagine that you are a scientist ina new recycling company in ‘singapore. You have been asked to develop a process to recycle ‘Chemistry in a Sustainable World © Chapter 21 Lets Asses Lets Reflect Application ‘one type of plastic waste collected from households and schools. STEM Project ‘You need to present your recommendations to your company Chief Executive Officer, Consider the following questions when coming up with your recommendations. + What are the common types of plastic waste that can be collected ‘rom households and schools? + Canall the plastic waste collected be recycled? + What method(s) of recycling plastics would you use? + What are the possible social, economic and environmental issues of recycling each type of plastic? + How can these issues be resolved? Problem-based Leaning: Practical Workbook rable hase Learning: Cool Career Materials Scientist ‘Amaterle seni dtermines ways tampons the properties of materi sucha polymer. cer she abo develops polymers wih new oF _desined properties or usin specific products For exanle. most pulymers donot condct decry, Thus, hey are wily use as elcid smsubtor. Evens theopen mindedness sand reslience of cme scentistlod ther to ‘Giscover that some pelymerscan be modifiod ‘hasaly wo condic decry (gute 21.3). 1 200, these sents wae Jot awarded the [Noel Prien Chemis forthe chcoveryand -deviepment of polymers thet conduct deci. Figure 21.36 light-emitting diodes (LEDs found in some electronic screens are made from polymers. 401Chapter 21 © Polymers ee ds‘Chemistry in a Sustainable World "© Chapter 27 eid Section A: Multiple-choice Questions 1) Which of the following diagrams best rapresents a saction of the structure cof Terylene? Od coin gie gach ed 2 which he foo statements about febyetene se et Fes not ect wth aqueous bromine 2. Rhauthe same epic xml isetere, 5 Mies condonsatonpohmer fA Vand20ny QB tard ony fe 2antaony Qt 2and3 2 Wich of the foowng compounds cn ‘undergo addition polymerisation? ee © A Vand2only QB land only ¢ 2and3ony Qo 1.2and3 4 Figure 21.37 shows the fll structural formula of butengdotc acid rai) Ha aCeCa Ce Cand Figure 2137 Which statement about butenedioic acid Is comect? Itundergoes a substitution reaction only. ‘tundergoes addition polymerisation only. Itundergoes condensation polymensation only, ‘undergoes both addition polymerisation and condensation polymerisation. |5 Which ofthe following can be represented by the empirical formula cH,? 1 2 3 & butane polyethene) palyipropene) only 2and 3 only 9 Bland 2only D 1.2and3, ‘Section B: Structured Quastions 11 Nylon is 2 polyamide that is made by condensation polymerisation. (a) ) 2a (o) ‘What is meant by polyamide? Draw the structure of nyion, showing twe repeat units. Figure 21.38 shows the structural formula of a monomer. Cac é 4, Figure 2138 ‘Draw the structure of the polymer formed by this monomer, showing three repeat units. Figure 21.39 shows a section of the structure ofa polymer. HHH HHO = Cu Cu CuCuCuce aqadakad Figure 21.39Polymers (), How many repeat units are shown in the structure? {Draw the ful structural formula ‘of the monomer and state its ‘molecular formula. 3. Poly(ethylene terephthalate) (PET)is produced by the reaction between ‘ethylene glycol and terephthalic acid gue 21.40). HOw Clin OH ive aot 40 ° ae Cie Ce OH Terephtat acid Figure21.40 (0) Draw the structure of PET, showing atleast two repeat units. (©) Dasenbe how Per can be convertad bback to ethylene glycol and terephthalic acid. 4 Poly(acrylonitril) is a synthetic fibre. Figure 2141 shows a section ofthe structute of polyiscrylonttrile) HOH HH AK CaCuCuCaCeCe WA ae Wwe Figura 211 (@) Draw the structural formula of acrylonitrile. (&) What type of polymer is ppolyacrylonitiley? (e), Would you expect polyacrytonitril) to conduct electricity in the molten state! Why! (c)_ State two gases that ae produced ‘when polyfacrylonitile fs burnt in ‘excess oxygen. 5 Figure 2142shows the structures of two ‘compounds, Xand ¥. Fiure2142 ‘When x andy react hydrogen chloride ‘gas gven off and polymer, 2. is (a), State the type of reaction that ‘occurs between x and ¥. (b) (D) Deduce the structure of FZ. () Suggest one use of polymer z. ‘Section C: Free-response Questions 1) Polystyrene is often used as packaging material. {@) The monomer for making polystyrene {sstyrene. The structural formula ‘ofstyrene is C.H,CH=CH, Draw the structure of polystyrene, showing ‘two repeat units, (©) Cracking is one way of recycling plastic waste. Suggest two ‘advantages of cacking over Incineration of plastic waste. {c)_ Suggest one environmental isue of recycling polystyrene, 2 Sodium polyacrylate is used to make disposable diapers because itis a ‘super-absorber which can absorb water ‘as much as 200 to 300 times its mass. Figure 21.43 shows part of the structure ‘of sodium polyacryiate. Figure 2143 (2) () Deduce the full structural ‘formula of the monomer used +0 form sodium polyacrylate. (The monomer used to form sodium polyacrylates the sodium salt of acrylic acid. Based fonyour answer in), deduce ‘the full structural formula of acrylic acd (b) The outer layer of a diaper is “waterproof. Suggest one polymer ‘that can be used to make the outer layer ofa diaper. ©). State one effect of the improper disposal of disposable diapers on the environment. pes