Chain structure network flow example

Corsten points out that a supply chain is a special type of network composed of multi-level logistic chains owned by legally separated companies. The focus in the supply chain is the coordination of flows of materials and information between these companies. Corsten s examples show the supply chain structure starting with raw materials up to the final consumer (Corsten/Gossinger 2001). 

The one general class of polymers that fall outside this concept is the thermoplastic elastomers, one example of which was discussed previously. These materials can be processed (and reprocessed) at high temperature, yet they maintain properties of cured rubber at use temperatures. This system functions by the formation of either hard plastic, crystalline, or ionic domains that, at use temperature, act as cross-link sites because multiple chains are involved in the domains. Upon heating, the integrity of these domains breaks down, and the polymer chains can easily flow past one another. It should be noted that at use temperatures these systems have a three-dimensional network. Such systems tend to show more creep and stress relaxation than cured systems, as the network is formed via weaker secondary effects rather than primary chemical bonds. These problems become more severe as the use temperature is increased because ultimately the network cannot remain intact at processing temperatures. For any network, its structure is important in defining the performance of the... 

Ic. Cross-Linking of Polymer Chains.—Formation of chemical bonds between linear polymer molecules, commonly referred to as cross-linking, also may lead to the formation of infinite networks. Vulcanization of rubber is the most prominent example of a process of this sort. Through the action of sulfur, accelerators, and other ingredients present in the vulcanization recipe, sulfide cross-linkages are created by a mechanism not fully understood (see Chap. XI). Vulcanized rubbers, being typical network structures, are insoluble in all solvents which do not disrupt the chemical structure, and they do not undergo appreciable plastic, or viscous, flow. 

When the number of repeating units in a polymer chain is low, that is when the molecular weight of the polymer is low (2000-10000 g mol ), the polymer is defined as a resin, provided it possesses sufficient numbers of active sites in its structures for chemical cross-linking to occur. The resins can form three-dimensional network structures if sufficient external energy (heat/light/radiation) is applied, with or without the use of any other chemical(s) in their finished state. They are free flowing materials of low viscosity. Polyester resins, epoxy resins, and polyurethane resins are examples of this type of polymer. This book contains descriptions of the different types of resins derived from various vegetable oils. 

Individual polymer chains in an ensemble can also be covalently joined to other chains around it at discrete points along it. This yields a 3D network of chains (or open-tree structures of chains or a mix of both). Cross-linking is desirable where insolubility and high mechanical strength are demanded of aplastic. Ideally, each and every chain will be linked to each other so that the entire ensemble of chains is a single giant molecule (this actually does occur in natural rubber when vulcanized or cross-linked.) An automobile or aircraft tire is an example of a fully cross-linked polymer. On heating, cross-linked polymers do not convert into a viscous liquid melt as the molecules are chemically linked to one another and cannot flow independently. 

The ownership structure of the distribution network can have as big an impact as the type of distribution network. The bulk of this chapter deals with different types of physical networks and subsequent flows to distribute products successfully. However, equally important is who owns each stage in the distribution network. Distribution networks that have exactly the same physical flow but different ownership structures can have vastly different performance. For example, a manufacturer that owns its distribution network can control the network s actions. However, if the manufacturer does not own the distribution network, as is more often the case, a wide variety of issues must be taken into account to optimize over the network. Obviously, an independent distributor wants to optimize its own enterprise, not necessarily the entire supply chain. Attempting to optimize over a distribution network with multiple enterprises reqnires great skill in coordinating the incentives of each of the players and in creating the right relationships. 

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