Several reasons are behind formation of odors in materials, including the following: - Use of other materials than polymer, especially materials required in processing - Use of various process parameters and their severity in degradation of components of formulation - Recycling of polymeric materials - Contact with natural products (food, cosmetics, etc.) - Storage - Migration-evaporation - Storage in the same space - Diffusion-related properties The above reasons are analyzed for different materials to find out the best methods to prevent odor formation. The book also contains information on testing of odor changes, relationship between odor and toxicity, and the selection of raw materials for fog-free products. The first book in this field, the Handbook of Odors in Materials is needed by anyone interested in materials. - The first book of its kind in this field - Analyzes the reasons behind odor formation and provides the best methods to prevent odors in various materials - Contains information on testing of odor changes and the relationship between odor and toxicity

George Wypych has a Ph.D. in chemical engineering. His professional expertise includes both university teaching (full professor) and research and development. He has published 18 books, 47 scientific papers, and he has obtained 16 patents. He specializes in polymer additives, polymer processing and formulation, material durability and the development of sealants and coatings.

3 DISTINCTIVE ODORS

Humans can smell many thousands of odorants with high precision (even slight changes in odorant structure are noticed by our sense of smell). Figure 3.1 shows the mechanics of action of the olfactory system. The olfactory epithelium contains three predominant cell types: the olfactory sensory neurons; the supporting cell; and the basal cell.1 Cilia contain the molecular machinery of olfactory transduction, including receptors, effector enzymes and ion channels.1 Cilia capture odorant characteristics and transmit them further through olfactory neuron axons to the olfactory bulb.1 Olfactory bulb cells help to shape sensory input and olfactory bulb output in several ways before this information is sent to higher centers in the brain.1 Humans are known to have 350 odorant receptors, which are able to recognize chemically diverse odorants.1 Odor discrimination involves a very large number of different odorant receptors, each responsive to a small set of odorants.1 Odorant receptors can have a broad receptive range.1 They can respond to more than one odorant, and often to odorants of more than one chemical class (e.g., aldehydes and alcohols).1 More than one odor receptor can be activated by the same odorant.1

Figure 3.1 A schematic diagram of the olfactory epithelium. Odor ants enter the nasal cavity, diffuse through the nasal mucous and interact with specific receptors on the dendritic cilia of olfactory sensory neurons. The signals initiated by this receptor binding are transduced into electrical signals within the cilia and are transmitted along the sensory neuron axons to the olfactory bulb in the brain. [Adapted, by permission, from Munger S D in Molecular Basis of Olfaction and Taste, Basic Neurochemistry, 8th Ed., Elsevier, 2012.]

Also, not every odorant receptor, activated by a particular odor, responds with the same efficacy to that odor.1 The identity of an individual odor is encoded by several differentially tuned odorant receptors and it is called a combinatorial odor code.1 The olfactory system responds to extremely low concentrations of odorants, and olfactory perception is believed to be extremely sensitive.1 It is theoretically possible that the limit of olfactory detection is a single molecule.1 More details on the mechanisms of operation of our sense of smell can be found elsewhere.1

In the separate sections below, different distinctive types of odors will be analyzed from the point of view of their origin (material or product in which this odor is formed) and the chemical composition of odorants which cause the formation of this distinctive odor in different materials.

3.1 SWEET, BLOSSOM-LIKE (FRUITY)

Sweet odor and taste is the most popular distinctive odor type detected. It is also frequently called blossom-like or fruity. Table 3.1 contains information on sources of odor, products in which odor was detected, and chemical composition of odorants most likely causing this odor.

Table 3.1

Sources of sweet odor.2-13

3.2 GRASSY

Table 3.2 contains information on sources of odor, products in which this odor was detected, and chemical composition of odorants most likely causing this odor.

Table 3.2

Sources of grassy odor.4, 5, 14

3.3 LIQUORICE

Liquorice is a Mediterranean herb which has roots having an astringent flavor that is extracted to mask unpleasant flavors, such as drugs.

A refillable poly(ethylene terephthalate) bottle was a source of off-odor in mineral water and soft drinks.3 Anetole was the substance detected, which was associated with liquorice odor.3

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