Chewing gum

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Chewing_gum

 

Chewing gum

An unwrapped stick of chewing gum
Type	Confectionery
Main ingredients	gum base, sweeteners, plasticizers, flavors, colors, polyols
Cookbook: Chewing gum   Media: Chewing gum

Chewing gum is a soft, cohesive substance designed in order to be chewed without being swallowed. Modern chewing gum is composed of gum base, sweeteners, softeners/plasticizers, flavors, colors, and, typically, a hard or powdered polyol coating. Its texture is reminiscent of rubber because of the physical-chemical properties of its polymer, plasticizer, and resin components, which contribute to its elastic-plastic, sticky, chewy characteristics.

History

Sticks of Fruit Stripe chewing gum.

 

The cultural tradition of chewing gum seems to have developed through a convergent evolution process, as traces of this habit have arisen separately in many of the early civilizations. Each of the early precursors to chewing gum were derived from natural growths local to the region and were chewed purely out the instinctual desire to masticate. Early chewers did not necessarily desire to derive nutritional benefits from their chewable substances, but at times sought taste stimuli and teeth cleaning or breath-freshening capabilities.

Chewing gum in many forms has existed since the Neolithic period. 6,000-year-old chewing gum made from birch bark tar, with tooth imprints, has been found in Kierikki in Finland. The tar from which the gums were made is believed to have antiseptic properties and other medicinal benefits. It is chemically similar to petroleum tar and is in this way different from most other early gum. The Mayans and Aztecs were the first to exploit the positive properties of gum, they used chicle, a natural tree gum, as a base for making a gum-like substance and to stick objects together in everyday use. Forms of chewing gums were also chewed in Ancient Greece. The Ancient Greeks chewed mastic gum, made from the resin of the mastic tree. Mastic gum, like birch bark tar, has antiseptic properties and is believed to have been used to maintain oral health. Both chicle and mastic are tree resins. Many other cultures have chewed gum-like substances made from plants, grasses, and resins.

Variations of early chewing gum worldwide 

Ancient civilization	Chewing gum precursor
Ancient Greece	Mastic tree bark
Ancient Maya	Chicle
Chinese	Ginseng plant roots
Eskimos	Blubber
Native Americans	Sugar pine and spruce sap
South Americans	Coca leaves
South Asia (India)	Betel nuts
United States (early settlers)	Tobacco leaves

Although chewing gum can be traced back to civilizations around the world, the modernization and commercialization of this product mainly took place in the United States. The American Indians chewed resin made from the sap of spruce trees. The New England settlers picked up this practice, and in 1848, John B. Curtis developed and sold the first commercial chewing gum called The State of Maine Pure Spruce Gum. In this way, the industrializing West, having forgotten about tree gums, rediscovered chewing gum through the First Americans. Around 1850 a gum made from paraffin wax, which is a petroleum product, was developed and soon exceeded the spruce gum in popularity. To sweeten these early gums, the chewer would often make use of a plate of powdered sugar, which they would repeatedly dip the gum in to maintain sweetness. William Semple filed an early patent on chewing gum, patent number 98,304, on December 28, 1869.

An image of a Colgan's Taffy Tolu Chewing Gum chromolithograph advertisement circa 1910

 

The first flavored chewing gum was created in the 1860s by John Colgan, a Louisville, Kentucky pharmacist. Colgan mixed with powdered sugar the aromatic flavoring tolu, a powder obtained from an extract of the balsam tree (Myroxylon), creating small sticks of flavored chewing gum he named "Taffy Tolu". Colgan also lead the way in the manufacturing and packaging of chicle-based chewing gum, derived from Manilkara chicle, a tropical evergreen tree. He licensed a patent for automatically cutting chips of chewing gum from larger sticks: US 966,160 "Chewing Gum Chip Forming Machine" August 2, 1910 and a patent for automatically cutting wrappers for sticks of chewing gum: US 913,352 "Web-cutting attachment for wrapping-machines" February 23, 1909 from Louisville, Kentucky inventor James Henry Brady, an employee of the Colgan Gum Company. 

Modern chewing gum was first developed in the 1860s when chicle was brought from Mexico by the former President, General Antonio Lopez de Santa Anna, to New York, where he gave it to Thomas Adams for use as a rubber substitute. Chicle did not succeed as a replacement for rubber, but as a gum, which was cut into strips and marketed as Adams New York Chewing Gum in 1871. Black Jack (1884), which is flavored with licorice, Chiclets (1899), and Wrigley's Spearmint Gum were early popular gums that quickly dominated the market and are all still around today. Chewing gum gained worldwide popularity through American GIs in WWII, who were supplied chewing gum as a ration and traded it with locals. Synthetic gums were first introduced to the U.S. after chicle no longer satisfied the needs of making good chewing gum. By the 1960s, US manufacturers had switched to butadiene-based synthetic rubber, as it was cheaper to manufacture.

Ingredient composition

Gum base composition is considered proprietary information known by select individuals within each gum-manufacturing company. Information about the other components of chewing gum are more accessible to the public and they are listed in Table 2.

Table 2: Common Ingredients in the Formulation of Modern Chewing Gum

Ingredient	Percent (by weight) Composition	Functionality	Common Examples
Gum Base	25-35%	Although the formulation of gum bases is considered proprietary information for industry competitors, three main components make up all gum bases: resin, wax, and elastomer. Resin (ex. terpene) is the main chewable portion. Wax softens the gum. Elastomers add flexibility. The molecular composition of gum base is very similar to that of plastics and rubbers.	Natural or Synthetic Ingredients (See Table 3)
Sweeteners	Sugar Alcohols: 40-50% Artificial Sweeteners: 0.05-0.5%	Bulk Polyol Sweeteners are responsible for initial sweetness, whereas intensive sweeteners are intended for prolonging the sweetness effect. Intensive Sweeteners are often encapsulated to delay the release of flavor.	Bulk Polyol Sweeteners[20]: sugar, dextrose, glucose or corn syrup, erythritol, isomalt, xylitol, maltitol, mannitol, sorbitol, lactitol	Intensive Sweeteners[21]: aspartame, acesulfame-K, saccharine, sucralose, neohesperidine, dihydrichalcone
Glycerine	2-15%	To maintain moistness.
Softener/Plasticizer	1-2%	To soften gum by increasing flexibility and reducing brittleness by altering the glass transition temperature. Quantities of this additive are altered in order to balance processability and packaging speed.	lecithin, hydrogenated vegetable oils, glycerol ester, lanolin, methyl ester, pentaerythritol ester, rice bran wax, stearic acid, sodium and potassium stearates
Flavors	1.5-3.0%	For taste and sensory appeal. Flavor components in gum exist in liquid, powder or micro-encapsulated forms. Liquid flavor incorporations are either water-soluble, oil-soluble, or water-dispersible emulsions. The oil-soluble flavors remain in the gum longer, resulting in longer lasting flavor sensations, because the gum base is hydrophobic and attracted to oil-based components.	Natural or synthetic Peppermint and spearmint are the most popular flavors. Food acids are implemented to provide a sour flavor (i.e. citric, tartaric, malic, lactic, adipic, and fumaric acids).
Colors	Variable	For visual appeal.	Natural or Synthetic
Polyol Coating	Variable	Pellet gum's characteristic hard outer shell is due to a polyol coating. Polyols can also be implemented as a water absorbent powder dusting in order to maintain the quality and extend the shelf life of the product. These humectants bind water by establishing many hydrogen bonds with water molecules.	Sorbitol Maltitol/Isomalt Mannitol Starch

Gum base

Gum base is made of polymers, plasticizers, and resins. Polymers, including elastomers, are responsible for the stretchy and sticky nature of chewing gum. Plasticizers improve flexibility and reduce brittleness, contributing to the plastic and elastic nature of gum. The interactions of plasticizers within gum base are governed by solubility parameters, molecular weight, and chemical structure. Resins compose the hydrophobic portion of the gum base, responsible for its chewiness. Although the exact ingredients and proportions used in each brand's gum base are trade secrets within the gum industry, Table 3 lists all of the natural and synthetic gum base components approved for use in the United States, demonstrating some examples of key gum base components.

Table 3: Gum Base Ingredients Approved for Use by the U.S. Food and Drug Administration (2016)

Natural Ingredients	Synthetic Ingredients
Sapotaceae Chicle Chiquibul Crown Gum Gutta hang kang Massaranduba balata Massaranduba chocolate Nispero Rosidinha Venezuelan chicle	Butadiene-styrene rubber Isobutylene-isoprene copolymer (butyl rubber) Paraffin (via the Fischer-Tropsch process) Petroleum wax Petroleum wax synthetic Polyethylene Polyisobutylene Polyvinyl acetate
Apocynaceae Jelutong Leche caspi (sorva) Pendare Perillo
Moraceae Leche de vaca Niger gutta Tunu (tuno)
Euphorbiaceae Chilte Natural rubber

Manufacturing process

First, gum base is previously prepared through a melting and straining or filtering process. The formulation for gum base is proprietary information known to few individuals within each gum-producing company. Next, other ingredients such as nutritive and non-nutritive sweeteners and flavors are added to the gum base until the warm mixture thickens like dough. The gum base mixture is heated during this mixing process in order to increase the entropy of the polymers to achieve a more uniform dispersion of ingredients. Then, extrusion technology is implemented to smooth, form, and shape the gum. Next, the gum goes through a shaping process that is determined by gum type and consumer demand. For example, cut and wrap (chunk or cube) pieces are severed straight out of the extruder using a vertical cutter. Sheeting is a technique often used for stick, slab and tab gums. Next, gum is either conditioned by being sprinkled with a powdered polyol or coated via the application of subsequent layers of coating using temperature controlled coating basins before it is sent to packaging.

Product varieties

Chewing gum balls

Chewing gum can come in a variety of formats ranging from 1.4 to 6.9 grams per piece, and products can be differentiated by the consumers’ intent to form bubbles or the sugar/sugarless dichotomy.

Chewing gum typically comes in three formats: tablets, coated pellets, and sticks/ slabs. Bubble gum typically come in three formats as well: tablets, hollow balls, and cubes or chunks. Stick, slab, and tab gums typically come in packs of about five to 17 sticks or more, and their medium size allows for softer texture. Pellet gums, or dragée gums, are pillow shaped pieces that are almost always coated. Packaging of pellet gums can vary from boxes to bottles to blister packs. The coating of pellet gum allows for the opportunity for multiple flavor sensations, since coating is done in a layering process and different flavor attributes can be added to various layers. Cube or chunk gums, which are typically intended for bubble blowing, are called cut and wrap gums as they are typically severed from continuous strands of extruded gum and packaged directly.

Quality and safety

Chewing gum is rather shelf stable because of its non-reactive nature and low moisture content. The water activity of chewing gum ranges from 0.40 to 0.65. The moisture content of chewing gum ranges from three to six percent. In fact, chewing gum retains its quality for so long that, in most countries, it is not required by law to be labeled with an expiration date. If chewing gum remains in a stable environment, over time the gum may become brittle or lose some of its flavor, but it will never be unsafe to eat. If chewing gum is exposed to moisture, over time water migration may occur, making the gum soggy. In lollipops with a gum center, water migration can lead to the end of the product's shelf life, causing the exterior hard candy shell to soften and the interior gum center to harden.

Physical and chemical characteristics

The physical and chemical properties of chewing gum impact all aspects of this product, from manufacturing to sensory perception during mastication. 

Chewiness

The polymers that make up the main component of chewing gum base are hydrophobic. This property is essential because it allows for retention of physical properties throughout the mastication process. Because the polymers of gum repel water, the water-based saliva system in a consumer's mouth will dissolve the sugars and flavorings in chewing gum, but not the gum base itself. This allows for gum to be chewed for a long period of time without breaking down in the mouth like conventional foods. Chewing gum can be classified as a product containing a liquid phase and a crystalline phase, providing gum with its characteristic balance of plastic and elastic properties.

Stickiness

While hydrophobic polymers beneficially repel water and contribute to chewiness, they also detrimentally attract oil. The stickiness of gum results from this hydrophobic nature, as gum can form bonds and stick when it makes contact with oily surfaces such as sidewalks, skin, hair, or the sole of one's shoe. To make matters worse, unsticking the gum is a challenge because the long polymers of the gum base stretch, rather than break. The sticky characteristic of gum may be problematic during processing if the gum sticks to any machinery or packaging materials during processing, impeding the flow of product. Aside from ensuring that the machinery is free from lipid-based residues, this issue can be combatted by the conditioning and coating of gum toward the end of the process. By adding either a powder or a coating to the exterior of the gum product, the hydrophobic gum base binds to the added substance instead of various surfaces with which it may come in contact.

Bubble-blowing capability

Bubblegum bubble.

 

Bubblegum bubbles are formed when the tension and elasticity of gum polymers acts against the constant and equally dispersed pressure of air being directed into the gum bolus. Bubble gum bubbles are circular because pressure from the focused air being directed into the bolus acts equally on all of the interior surfaces of the gum cud, uniformly pushing outward on all surfaces as the polymers extend. As the bubble expands, the polymers of the gum base stretch and the surface of the bubble begins to thin. When the force of the air being blown into the bubble exceeds the force that the polymers can withstand, the polymers overextend and the bubble pops. Due to the elastic attributes of chewing gum, the deflated bubble recoils and the wad of gum is ready to continue being chewed.

Gum bases with higher molecular weights are typically used in gums intended to meet bubble-forming expectations. Higher molecular weight gum bases include longer polymers that are able to stretch further, and thus are able to form larger bubbles that retain their shape for a longer time.

Flavor release

Flavor delivery is extended throughout the mastication process by timed release of different flavor components due to the physical-chemical properties of many of chewing gum's ingredients. Entropy is a key player in the process of flavor delivery; because some gum components are more soluble in saliva than gum base and because over time flavor components desire to increase their entropy by becoming dispersed in the less ordered system of the mouth than in the more ordered system of the gum bolus, flavor delivery occurs. During the first three to four minutes of the chew, bulking agents such as sugar or sorbitol and maltitol have the highest solubility and, therefore, are chewed out first. As these components dissolve in the consumers’ saliva and slide down the esophagus, they are no longer retained in the gum base or perceived by the chewer. During the next phase of the chew in the four to six minute range, intense sweeteners and some acids are dissolved and chewed out. These components last slightly longer than the bulking agents because they have a slightly lower solubility. Next, encapsulated flavors are released during either 10-15 minute into the chew or after 30–45 minutes. Encapsulated flavors remain incorporated in the gum base longer because the molecules that they are encapsulated in are more easily held within the gum matrix. Finally, during the last phase of the chew, softeners such as corn syrup and glycerin and other textural modifiers are dissolved, resulting in a firming up of the gum and the end of the chew.

Studies have shown that gum flavor is perceived better in the presence of sweetener. Companies have started to create chemical systems in gum so that the sweetener and flavor release together in a controlled manner during chewing.

Cooling sensation

A cooling sensation is achieved through the chemical phenomenon of the negative enthalpy of dissolution that occurs with bulk sweeteners, such as the sugar alcohols. The enthalpy of dissolution refers to the overall amount of heat that is absorbed or released in the dissolving process. Because the bulk sweeteners absorb heat as they dissolve and have a negative enthalpy, they yield a cooling sensation as they are dissolved in a consumer's saliva.

Health effects

Brain function

A review about the cognitive advantages of chewing gum by Onyper et al. (2011) found strong evidence of improvement for the following cognitive domains: working memory, episodic memory and speed of perception. However the improvements were only evident when chewing took place prior to cognitive testing. The precise mechanism by which gum chewing improves cognitive functioning is however not well understood. The researchers did also note that chewing-induced arousal could be masked by the distracting nature of chewing itself, which they named "dual-process theory", which in turn could explain some of the contradictory findings by previous studies. They also noticed the similarity between mild physical exercise such as pedaling a stationary bike and chewing gum. It has been demonstrated that mild physical exercise leads to little cognitive impairment during the physical task accompanied by enhanced cognitive functioning afterwards. Furthermore, the researchers noted that no improvement could be found for verbal fluency, which is in accordance with previous studies. This finding suggests that the effect of chewing gum is domain specific. The cognitive improvements after a period of chewing gum have been demonstrated to last for 15–20 minutes and decline afterwards.

Dental health

Sugar-free gum sweetened with xylitol has been shown to reduce cavities and plaque. The sweetener sorbitol has the same benefit, but is only about one-third as effective as xylitol. Other sugar substitutes, such as maltitol, aspartame and acesulfame K, have also been found to not cause tooth decay. Xylitol is specific in its inhibition of Streptococcus mutans, bacteria that are significant contributors to tooth decay. Xylitol inhibits Streptococcus mutans in the presence of other sugars, with the exception of fructose. Xylitol is a safe sweetener that benefits teeth and saliva production because, unlike most sugars, it is not fermented to acid. Daily doses of xylitol below 3.44 grams are ineffective and doses above 10.32 grams show no additional benefit. Other active ingredients in chewing gum include fluoride, which strengthens tooth enamel, and p-chlorbenzyl-4-methylbenzylpiperazine, which prevents travel sickness. Chewing gum also increases saliva production.

Food and sucrose have a demineralizing effect upon enamel that has been reduced by adding calcium lactate to food. Calcium lactate added to toothpaste has reduced calculus formation. One study has shown that calcium lactate enhances enamel remineralization when added to xylitol-containing gum, but another study showed no additional remineralization benefit from calcium lactate or other calcium compounds in chewing-gum.

Other studies indicated that the caries preventive effect of chewing sugar-free gum is related to the chewing process itself rather than being an effect of gum sweeteners or additives, such as polyols and carbamide. A study investigated the in situ effect of casein phosphopeptide–amorphous calcium phosphate (CPP–ACP) found that its incorporation into a sugar-free gum increases the remineralization / protection of eroded enamel surface significantly.

Gum chewing is regarded as a helpful way to cure halitosis (bad breath). Chewing gum not only helps to add freshness to breath but can aid in removing food particles and bacteria associated with bad breath from teeth. It does this by stimulating saliva, which essentially washes out the mouth. Chewing sugar-free gum for 20 minutes after a meal helps prevent tooth decay, according to the American Dental Association, because the act of chewing the sugar-free gum produces saliva to wash away bacteria, which protects teeth. Chewing gum after a meal replaces brushing and flossing, if that's not possible, to prevent tooth decay and increase saliva production. Chewing gum can also help with the lack of saliva or xerostomia since it naturally stimulates saliva production. Saliva is made of chemicals, such as organic molecules, inorganic ions and macromolecules. 0.5% of saliva deals with dental health, since tooth enamel is made of calcium phosphate, those inorganic ions in saliva help repair the teeth and keep them in good condition. The pH of saliva is neutral, which having a pH of 7 allows it to remineralize tooth enamel. Falling below a pH of 5.5 (which is acidic) causes the saliva to demineralize the teeth.

Masumoto et al. looked at the effects of chewing gum after meals following an orthodontic procedure, to see if chewing exercises caused subjects pain or discomfort, or helped maintain a large occlusal contact area. 35 adult volunteers chewed gum for 10 to 15 minutes before or after three meals each day for 4 weeks. 90% of those questioned said that the gum felt "quite hard", and half reported no discomfort.

Use in surgery

Several randomized controlled studies have investigated the use of chewing gum in reducing the duration of post-operative ileus following abdominal and specifically gastrointestinal surgery. A systematic review of these suggests gum chewing, as a form of "sham feeding", is a useful treatment therapy in open abdominal or pelvic surgery, although the benefit is less clear when laparoscopic surgical techniques are used.

Chewing gum after a colon surgery helps the patient recover sooner. If the patient chews gum for fifteen minutes for at least four times per day, it will reduce their recovery time by a day and a half. The average patient took 0.66 fewer days to pass gas and 1.10 fewer days to have a bowel movement. Saliva flow and production is stimulated when gum is chewed. Gum also gets digestive juices flowing and is considered "sham feeding". Sham feeding is the role of the central nervous system in the regulation of gastric secretion.

Stomach

Chewing gum is used as a novel approach for the treatment of gastroesophageal reflux disease (GERD). One hypothesis is that chewing gum stimulates the production of more bicarbonate-containing saliva and increases the rate of swallowing. After the saliva is swallowed, it neutralizes acid in the esophagus. In effect, chewing gum exaggerates one of the normal processes that neutralize acid in the esophagus. However, chewing gum is sometimes considered to contribute to the development of stomach ulcers. It stimulates the stomach to secrete acid and the pancreas to produce digestive enzymes that aren't required. In some cases, when consuming large quantities of gum containing sorbitol, gas and/or diarrhea may occur.

Controversies

Classification as food

Controversy arises as to health concerns surrounding the questionable classification of gum as food, particularly in regard to some alternative uses for gum base ingredients. According to the U.S. Food and Drug Administration (FDA), chewing gum is considered a food, as the term “food” means “a raw, cooked, or processed edible substance, ice, beverage, or ingredient used or intended for use or for sale in whole or in part for human consumption, or chewing gum”. Chewing gum is defined as a food of minimal nutritional value. However, many of the ingredients in gum base have uses in inedible products, which raises concern in some consumers. Polyethylene, one of the most popular components of gum base, belongs to a common group of plastics and is used in products from plastic bags to hula hoops. Polyvinyl acetate is a sticky polymer found in white glue. Butyl rubber is typically used in caulking and the lining of car tires, in addition to its role in gum base. Paraffin wax is a byproduct of refined petroleum.

Possible carcinogens

Concern has arisen about the possible carcinogenicity of the vinyl acetate (acetic acid ethenyl ester) used by some manufacturers in their gum bases. Currently, the ingredient can be hidden in the catch-all term "gum base". The Canadian government at one point classified the ingredient as a "potentially high hazard substance." However, on January 31, 2010, the Government of Canada's final assessment concluded that exposure to vinyl acetate is not considered to be harmful to human health. This decision under the Canadian Environmental Protection Act (CEPA) was based on new information received during the public comment period, as well as more recent information from the risk assessment conducted by the European Union.

Choking and excretion of swallowed gum

Various myths hold that swallowed gum will remain in a human's stomach for up to seven years, as it is not digestible. According to several medical opinions, there seems to be little truth behind the tale. In most cases, swallowed gum will pass through the system as quickly as any other food.

There have been cases where swallowing gum has resulted in complications in young children requiring medical attention. A 1998 paper describes a four-year-old boy being referred with a two-year history of constipation. The boy was found to have "always swallowed his gum after chewing five to seven pieces each day", being given the gum as a reward for good behavior, and the build-up resulted in a solid mass which could not leave the body. A 1½-year-old girl required medical attention when she swallowed her gum and four coins, which got stuck together in her esophagus. A bezoar is formed in the stomach when food or other foreign objects stick to gum and build up, causing intestinal blockage. As long as the mass of gum is small enough to pass out of the stomach, it will likely pass out of the body easily, but it is recommended that gum not be swallowed or given to young children who do not understand not to swallow it.

Adults have choked to death on chewing gum in rare cases. A 2012 report describes a 42-year-old woman who fell on the stairs while chewing gum. Due to the impact, the gum fell into the pharynx and was inhaled into the larynx, causing complete blockage and resulting in the woman's death by asphyxiation.

Environmental effects

Chewing gum on a sidewalk in Reykjavík

 

Chewing gum is not water-soluble and unlike other confectionery is not fully consumed. There has been much effort at public education and investment aimed at encouraging responsible disposal. Despite this it is commonly found stuck underneath benches, tables, handrails and escalators. It is extremely difficult and expensive to remove once "walked in" and dried. Gum bonds strongly to asphalt and rubber shoe soles because they are all made from polymeric hydrocarbons. It also bonds strongly with concrete paving. Removal is generally achieved by steam jet and scraper but the process is slow and labour-intensive.

Most external urban areas with high pedestrian traffic show high incidence of casual chewing gum discard. In 2000 a study on Oxford Street, one of London's busiest shopping streets, showed that a quarter of a million black or white blobs of chewing gum were stuck to its pavement. Gum removal from city streets, or even famous landmarks, can be a costly effort; in Rome, 15,000 pieces of chewed gum are discarded on a daily basis and the removal of each piece costs the city one euro. However, likely as a consequence of Singapore's ban, Singapore's pavements are, perhaps uniquely amongst modern cities, free of gum. 

Various teams of researchers have developed gum that is less adhesive and degrades within days or weeks. One example, Rev7 Gum, was briefly for sale from 2010 to 2012. 

Bans

Many schools do not allow chewing gum because students often dispose of it inappropriately (leaving it under desks and chairs, behind vending machines, etc.). The chewing may also pose a distraction to class, and the gum might carry diseases or bacteria from other students.

The Singapore government outlawed chewing gum in 1992 citing the danger of discarded gum being wedged in the sliding doors of underground trains and general cleanliness. However, in 2004 the government allowed sugarless gum to be sold in pharmacies if a doctor or dentist prescribed it due to the Singapore–United States Free Trade Agreement.

Recycling

Gumdrop chewing gum collecting bin

 

In 2018, the BBC published a news article on British designer Anna Bullus, who created a method of collecting and recycling chewing gum into plastic, noting that litter from chewing gum is the second most common form of litter, second only to cigarette litter. She uses a Worcester recycling plant to make old chewing gum into plastic. She then uses that plastic at a plastic moulding specialist, Amber Valley, in Leicester to make plastic objects. Known objects made are collection containers for more chewing gum, shoe soles, rubber boots, and plastic cups. Her company advertises itself as the "first company in the world to recycle and process chewing gum into a range of new compounds that can be used in the rubber and plastics industry". The company is called Gum-tec, and the collection containers are dubbed "gumdrops". Advertised products on the website are pencils, coffee mugs, guitar picks, a "bicycle spoke", rulers, sports cones, frisbees, boomerangs, door stops, "meal mates", lunch-boxes, and combs.

Butyl rubber

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Butyl_rubber

 

Butyl rubber gloves

 

Butyl rubber, sometimes just called "butyl", is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C₄H₈)_n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based. Butyl rubber is produced by polymerization of about 98% of isobutylene with about 2% of isoprene. Structurally, polyisobutylene resembles polypropylene, but has two methyl groups substituted on every other carbon atom, rather than one. Polyisobutylene is a colorless to light yellow viscoelastic material. It is generally odorless and tasteless, though it may exhibit a slight characteristic odor. 

Butyl rubber has excellent impermeability, and the long polyisobutylene segments of its polymer chains give it good flex properties. Its formula is:

 

It can be made from the monomer isobutylene (CH₂=C(CH₃)₂) only via cationic addition polymerization.

A synthetic rubber, or elastomer, butyl rubber is impermeable to air and used in many applications requiring an airtight rubber. Polyisobutylene and butyl rubber are used in the manufacture of adhesives, agricultural chemicals, fiber optic compounds, ball bladders, O-rings, caulks and sealants, cling film, electrical fluids, lubricants (2 stroke engine oil), paper and pulp, personal care products, pigment concentrates, for rubber and polymer modification, for protecting and sealing certain equipment for use in areas where chemical weapons are present, as a gasoline/diesel fuel additive, and chewing gum. The first major application of butyl rubber was tire inner tubes. This remains an important segment of its market even today.

History

Isobutylene was discovered by Michael Faraday in 1825. Polyisobutylene (PIB) was first developed by the BASF unit of IG Farben in 1931 using a boron trifluoride catalyst at low temperatures and sold under the trade name Oppanol B [de]. PIB remains a core business for BASF to this day.

It was later developed into butyl rubber in 1937, by researchers William J. Sparks and Robert M. Thomas, at Standard Oil of New Jersey's Linden, N.J., laboratory. Today, the majority of the global supply of butyl rubber is produced by two companies, ExxonMobil (one of the descendants of Standard Oil) and Polymer Corporation, a Canadian federal crown corporation established in 1942 to produce artificial rubber to substitute for overseas supply cut off by World War II. It was renamed Polysar in 1976 and the rubber component became a subsidiary, Polysar Rubber Corp. The company was privatized in 1988 with its sale to NOVA Corp which, in turn, sold Polysar Rubber in 1990 to Bayer AG of Germany. In 2005 Bayer AG spun off chemical divisions, including most of the Sarnia site, creating LANXESS AG, also of Germany.

PIB homopolymers of high molecular weight (100,000–400,000 or more) are polyolefin elastomers: tough extensible rubber-like materials over a wide temperature range; with low density (0.913–0.920), low permeability and excellent electrical properties.

In the 1950s and 1960s, halogenated butyl rubber (halobutyl) was developed, in its chlorinated (chlorobutyl) and brominated (bromobutyl) variants, providing significantly higher curing rates and allowing covulcanization with other rubbers such as natural rubber and styrene-butadiene rubber. Halobutyl is today the most important material for the inner linings of tubeless tires. Francis P. Baldwin received the 1979 Charles Goodyear Medal for the many patents he held for these developments. 

In the spring of 2013 two incidents of PIB contamination in the English Channel, believed to be connected, were described as the worst UK marine pollution 'for decades'. The RSPB estimated over 2,600 seabirds were killed by the chemical and hundreds more were rescued and decontaminated.

Uses

Fuel and lubricant additive

Polyisobutylene can be reacted with maleic anhydride to make polyisobutenylsuccinic anhydride (PIBSA), which can then be converted into polyisobutenylsuccinimides (PIBSI) by reacting it with various ethyleneamines. When used as an additive in lubricating oils and motor fuels, they can have a substantial effect on the properties of the oil or fuel. Polyisobutylene added in small amounts to the lubricating oils used in machining results in a significant reduction in the generation of oil mist and thus reduces the operator's inhalation of oil mist. It is also used to clean up waterborne oil spills as part of the commercial product Elastol. When added to crude oil it increases the oil's viscoelasticity when pulled, causing the oil to resist breakup when it is vacuumed from the surface of the water.

As a fuel additive, polyisobutylene has detergent properties. When added to diesel fuel, it resists fouling of fuel injectors, leading to reduced hydrocarbon and particulate emissions. It is blended with other detergents and additives to make a "detergent package" that is added to gasoline and diesel fuel to resist buildup of deposits and engine knock.

Polyisobutylene is used in some formulations as a thickening agent.

Explosives

Polyisobutylene is often used by the explosives industry as a binding agent in plastic explosives such as C-4. Polyisobutylene binder is used because it makes the explosive more insensitive to premature detonation as well as making it easier to handle and mold. 

Speakers and Audio Equipment

Butyl rubber is generally used in speakers, specifically the surrounds. It was used as a replacement for foam surrounds because the foam would deteriorate. The majority of modern speakers use butyl rubber, while most vintage speakers use foam. 

Sporting equipment

Butyl rubber is used for the bladders in sporting balls (e.g. Rugby balls, footballs, basketballs, netballs) to provide a tough, airtight inner compartment.

Damp proofing and roof repair

Butyl rubber sealant is used for damp proofing, rubber roof repair and for maintenance of roof membranes (especially around the edges). It is important to have the roof membrane fixed, as a lot of fixtures (e.g., air conditioner vents, plumbing, and other pipes) can considerably loosen it.

Rubber roofing typically refers to a specific type of roofing materials that are made of ethylene propylene diene monomers (EPDM rubber). It is crucial to the integrity of such roofs to avoid using harsh abrasive materials and petroleum-based solvents for their maintenance.

Polyester fabric laminated to butyl rubber binder provides a single-sided waterproof tape that can be used on metal, PVC, and cement joints. It is used for repairing and waterproofing metal roofs. 

Gas masks and chemical agent protection

Butyl rubber is one of the most robust elastomers when subjected to chemical warfare agents and decontamination materials. It is a harder and less porous material than other elastomers, such as natural rubber or silicone, but still has enough elasticity to form an airtight seal. While butyl rubber will break down when exposed to agents such as NH₃ (ammonia) or certain solvents, it breaks down more slowly than comparable elastomers. It is therefore used to create seals in gas masks and other protective clothing. 

Pharmaceutical stoppers

Butyl and bromobutyl rubber are commonly used for manufacturing rubber stoppers used for sealing medicine vials and bottles.

Chewing gum

Gumdrop chewing gum collecting bin

 

Most modern chewing gum uses food-grade butyl rubber as the central gum base, which contributes not only the gum's elasticity but an obstinate, sticky quality which has led some municipalities to propose taxation to cover costs of its removal.

Recycled chewing gum has also been used as a source of recovered polyisobutylene. Amongst other products, this base rubber has been manufactured into coffee cups and 'Gumdrop' gum-collecting bins. When filled, the collecting bins and their contents are shredded together and recycled again. 

Tires

Butyl rubber and halogenated rubber are used for the innerliner that holds the air in the tire.

Insulating Windows

Polyisobutylene is used as the primary seal in an insulating glass unit for commercial and residential construction providing the air and moisture seal for the unit.

Chloroprene

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Chloroprene

 

Chloroprene

Names
IUPAC name 2-Chlorobuta-1,3-diene
Other names Chloroprene, 2-chloro-1,3-butadiene, Chlorobutadiene, β-Chloroprene
Identifiers
CAS Number	126-99-8
3D model (JSmol)	Interactive image
ChEBI	CHEBI:39481
ChEMBL	ChEMBL555660
ChemSpider	29102
ECHA InfoCard	100.004.381
KEGG	C19208
PubChem CID	31369
RTECS number	EL9625000
CompTox Dashboard (EPA)	DTXSID5020316
Properties
Chemical formula	C4H5Cl
Molar mass	88.5365 g/mol
Appearance	Colorless liquid
Odor	pungent, ether-like
Density	0.9598 g/cm3
Melting point	−130 °C (−202 °F; 143 K)
Boiling point	59.4 °C (138.9 °F; 332.5 K)
Solubility in water	0.026 g/100 mL
Solubility	soluble in alcohol, diethyl ether miscible in ethyl ether, acetone, benzene
Vapor pressure	188 mmHg (20 °C)
Refractive index (nD)	1.4583
Hazards
Main hazards	Highly flammable, irritant, toxic.
R-phrases (outdated)	R45, R11, R20/22, R36/37/38, R48/20
S-phrases (outdated)	S53, S45
NFPA 704 (fire diamond)	3 2 0
Flash point	−15.6 °C (3.9 °F; 257.5 K)
Explosive limits	1.9%–11.3%
Lethal dose or concentration (LD, LC):
LD50 (median dose)	450 mg/kg (rat, oral)
LC50 (median concentration)	3207 ppm (rat, 4 hr)
LCLo (lowest published)	1052 ppm (rabbit, 8 hr) 350 ppm (cat, 8 hr)
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 25 ppm (90 mg/m3) [skin]
REL (Recommended)	Ca C 1 ppm (3.6 mg/m3) [15-minute]
IDLH (Immediate danger)	300 ppm
Related compounds
Related Dienes	Butadiene Isoprene
Related compounds	Vinyl chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Chloroprene is the common name for 2-chlorobuta-1,3-diene (IUPAC name) with the chemical formula CH₂=CCl−CH=CH_2. Chloroprene is a colorless volatile liquid, almost exclusively used as a monomer for the production of the polymer polychloroprene, a type of synthetic rubber. Polychloroprene is better known as Neoprene, the trade name given by DuPont.

History

Although it may have been discovered earlier, the chemistry of chloroprene was largely developed by DuPont during the early 1930s, specifically with the formation of neoprene in mind. The chemists Elmer K. Bolton, Wallace Carothers, Arnold Collins and Ira Williams are generally accredited with its development and commercialisation although the work was based upon that of Julius Arthur Nieuwland, with whom they collaborated.

Production

Chloroprene is produced in three steps from 1,3-butadiene: (i) chlorination, (ii) isomerization of part of the product stream, and (iii) dehydrochlorination of 3,4-dichlorobut-1-ene.

Chlorine adds to 1,3-butadiene to afford a mixture of 3,4-dichlorobut-1-ene and 1,4-dichlorobut-2-ene. The 1,4-dichloro isomer is subsequently isomerized to 3,4 isomer, which in turn is treated with base to induce dehydrochlorination to 2-chlorobuta-1,3-diene. This dehydrohalogenation entails loss of a hydrogen atom in the 3 position and the chlorine atom in the 4 position thereby forming a double bond between carbons 3 and 4. In 1983, approximately 2,000,000 kg was produced in this manner. The chief impurity in chloroprene prepared in this way is 1-chlorobuta-1,3-diene, which is usually separated by distillation. 

Acetylene process

Until the 1960s, chloroprene production was dominated by the "acetylene process," which was modeled after the original synthesis of vinylacetylene. In this process, acetylene is dimerized to give vinyl acetylene, which is then combined with hydrogen chloride to afford 4-chloro-1,2-butadiene (an allene derivative), which in the presence of copper(I) chloride, rearranges to the targeted 2-chlorobuta-1,3-diene.

This process is energy-intensive and has high investment costs. Furthermore, the intermediate vinyl acetylene is unstable. This "acetylene process" has been replaced by a process, which adds Cl₂ to one of the double bonds in 1,3-butadiene, and subsequent elimination produces HCl instead, as well as chloroprene.

Regulations

 

Transportation

Transportation of uninhibited chloroprene has been banned in the United States by the US Department of Transportation. Stabilized chloroprene is in hazard class 3 (flammable liquid). Its UN number is 1991 and is in packing group 1. 

Occupational health and safety

Hazards

GHS hazard pictograms that apply to chloroprene. From left: flammability; carcinogenicity, mutagenicity, reproductive toxicity, respiratory sensitization, target organ toxicity, or aspiration toxicity; irritant (skin and eye), skin sensitizer, respiratory tract irritant, hazardous to ozone layer, may have narcotic effects; aquatic toxicity; and acute toxicity (fatal or toxic).

 

As a way to visually communicate hazards associated with chloroprene exposure, the United Nations Globally Harmonized System of Classification and Labeling of Chemicals (GHS) has designated the following hazards for exposure to chloroprene: flammable, toxic, dangerous to the environment, health hazard and irritant. Chloroprene poses fire hazard (flash point -4 °F). OSHA identifies chloroprene as a category 2 flammable liquid and emphasizes that at least one portable fire extinguisher should be within 10 and no more than 25 feet away from the flammable liquid storage area. OSHA provides resources on addressing flammable liquids at industrial plants which is where the likely exposure to chloroprene exists (see external resources). As a vapor, chloroprene is heavier than air. 

According to the National Fire Protection Association's rating system, chloroprene is designated with a category 2 health hazard (temporary incapacitation or residual injury), a category 3 fire hazard (ignition under the presence of moderate heat), and a category 1 reactivity (unstable at high temperatures and pressures).

Chronic exposure to chloroprene may have the following symptoms: liver function abnormalities, disorders of the cardiovascular system, and depression of the immune system.

The Environmental Protection Agency(EPA) designated chloroprene as likely to be carcinogenic to humans based on evidence from studies that showed a statistically significant association between occupational chloroprene exposure and the risk of lung cancer. As early as 1975, NIOSH had identified the potential health hazards of chloroprene in their bulletin primarily citing two Russian cohort studies from those working with chloroprene in an occupational setting.

Hazard determination

OSHA defines hazard determination as "the process of evaluating available scientific evidence in order to determine if a chemical is hazardous pursuant to the HCS." While chemical manufacturers and importers are required to conduct a hazard determination, other companies may voluntarily conduct a hazard determination to ensure worker health and safety. Under the hazard determination framework, any chemical that has a physical or health hazard is considered a hazardous chemical. Physical hazards include fire hazards, reactive hazards, and explosion hazards. Heath hazards include systemic effects and target organ effects. Chloroprene is on OSHA's list for substances that are regulated as toxic and hazardous.

In the European Union, the hazard-determination-equivalent is the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation enacted on June 1, 2007 by the European Chemicals Agency (ECHA). The goal of REACH is to "improve the protection of human health and the environment from the risks that can be posed by chemicals, while enhancing the competitiveness of the EU chemicals industry." If risks of chemicals are unmanageable, ECHA may ban its use. 

Hazard controls

Several epidemiological studies and toxicological reports provide evidence of chloroprene's capability to inflict occupational health and safety concerns. However, varying reviews of the degree to which chloroprene should be held responsible for health concerns highlight the criticality of sound scientific research. Nonetheless, health and safety practices should always be implemented in the workplace. Some of these occupational concerns include: cleaning equipment or unclogging pipes coated with chloroprene, inhaling chloroprene off-gas, chloroprene spontaneously reacting with other chemicals and chloroprene inducing a workplace fire. Upon the clogging of equipment associated with occupational chloroprene use, employers should ensure that their employees are wearing the proper PPE and set up administrative controls so that skin exposure to and inhalation of chloroprene is avoided. Only one fatality as a result of chloroprene intoxication has been recorded which was a result of cleaning a container used for chloroprene.

NIOSH Hierarchy of Controls

 

The primary occupational concern for chloroprene is limited to the facilities producing chloroprene and using chloroprene to produce the synthetic rubber, polychloroprene. NIOSH developed a list of actions to address specific workplace hazards. These actions are represented in their diagram of the "Hierarchy of Controls" shown below with the most effective steps at the top and the least effective at the bottom. 

The high vaporization potential and flammability of chloroprene has significant implications for handling and storage operations in the occupational setting. Chloroprene should be stored in closed containers in a cool, well-ventilated area with the temperature no higher than 50 degrees Fahrenheit. In addition, chloroprene has a high reactivity and should be stored away from oxidizing agents such as perchlorate, peroxides, permanganates, chlorates, nitrates, chlorine, bromine, and fluorine. All activities inducing a potential fire hazard should be avoided. For instance, smoking, having open flames or using sparking tools to open or close storage containers should be prohibited. It is also advised that grounded and bonded metal containers are used for the transport of chloroprene.

Occupational exposure limits

The official legal body that develops and enforces occupational exposure limits (OEL) in order to ensure workplace safety and health regulations is the Occupational Health and Safety Administration (OSHA) that works under the U.S. Department of Labor. OSHA's permissible exposure limits (PELs), a guideline for occupational exposures, were adopted from the 1968 threshold limit values (TLVs) of the American Conference of Governmental Industrial Hygienists (ACGIH). Each year, the ACGIH publish their TLV and BEI booklet that provides updated information on "occupational exposure guidelines for more than 700 chemical substances and physical agents." The scientific literature on certain chemical and physical exposures has evolved since 1968, therefore OSHA recognizes that their PELs may not guarantee worker health and safety. The National Institute for Occupational Health and Safety (NIOSH) under the U.S. Department of Health and Human Services compensates for the rigidity of the PEL by researching "all medical, biological, engineering, chemical, and trade information relevant to the hazard" and publishing recommended exposure limits (RELs) based on their research. Therefore, as a way to ensure worker safety and health, the following sections on safety guidelines and hazard control will consider the most recent occupational exposure limits from ACGIH's 2018 TLV and BEI booklet and NIOSH's REL.

A table of occupational exposure limits (OELs) from various jurisdictions follows. In general, the OELs range from 0.55 ppm to 25 ppm.

Occupational Exposure Limits for Chloroprene

In the ACGIH's 2018 TLV and BEI booklet, chloroprene was designated with a skin and an A2 notation. The skin notation designation is based on animal and human research that have shown chloroprene's ability to be absorbed by the skin. An A2 designation by the ACGIH means that the substance is a suspected human carcinogen with support from human data that are accepted as adequate in quality but may not be enough to declare an A1 (known human carcinogen) designation. Additionally, the TLV basis for these designations are due to scientific studies that show an association between chloroprene exposure and lung cancer, upper respiratory tract (URT) and eye irritation.

Public health implications

Since chloroprene usage is limited to those facilities producing Neoprene, the occupational health risks are isolated to those facilities. However, insufficient control of chloroprene emissions may extend the health and safety concerns of chloroprene beyond the facility and into the surrounding areas. Chloroprene release is predominately as an air pollutant, but other feasible fates and transport of chloroprene in the environment are discussed below.

In the fourteenth edition of the National Institute of Health report on carcinogens, the half-life time differences between chloroprene in air, water and soil were highlighted. In the air, chloroprene “reacts with photo-chemically generated hydroxyl radicals” and has a half-life of 18 hours. The smaller amounts that are removed by reaction with ozone have a half-life of 10 days. In streams, chloroprene is stated to volatilize quickly with a half-life of 3 hours. However, in bigger bodies of water such as a lake, the half-life of chloroprene is 4 days. Similar to its reaction with water, chloroprene on soil was cited to volatilize from the surface. However, the report remarked that chloroprene holds the potential to leach into groundwater supplies. Due to its volatility and extreme reactivity, the threat of chloroprene exists predominantly as an air pollutant and is not expected to bioaccumulate or persist in the environment according to the U.S EPA Toxicological Review of Chloroprene. However, the Centers for Disease Control and Prevention (CDC) states that chloroprene does, in fact, have the potential to persist in the environment. Nonetheless, the primary route of exposure for animals and humans is inhalation, but can be absorbed through the skin or indigestion.

In December 2015, the EPA released its 2011 National Air Toxic Assessment to help state and local agencies prioritize the required steps in identifying and mitigating sources of air pollution. In this report, it was measured that chloroprene was being released from Denka Performance Elastomer's Pontchartrain facility located in LaPlace, Louisiana. EPA worked with the Louisiana Department of Environmental Quality, DuPont and the nonprofit organization Louisiana Environmental Action Network to institute monitoring of chloroprene pollution near the facility and in the surrounding neighborhood. Air monitoring is ongoing.