Step curing

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

Hand Lay-Up and Spray-Up. In hand lay-up, fiber reinforcements in mat or woven form are placed on the mold surface and then saturated with a Hquid polymer, typicaHy a polyester resin, that has been chemically activated to polymerize (cure) without the addition of heat. Multiple pHes of reinforcement and multiple cure steps aHow very heavy waH thicknesses to be achieved. 

At this point in the process, thermoplastic and chlorosulfonated polyethylene (CSPE) membranes are complete and are ready for packaging. In the case of ethylene—propylene—diene monomer (EPDM), the curing step occurs before the membrane is ready for packaging. The curing process is accomphshed by placing the membrane in a large vulcanizer where the material is heated under pressure to complete the cure. 

Another process for silicon carbide fibers, developed by Verbeek and Winter of Bayer AG [45], also is based on polymeric precursors which contain [SiCH2] units, although linear polysilmethylenes are not involved. The pyrolysis of tetramethylsilane at 700°C, with provision for recycling of unconverted (CHg Si and lower boiling products, gave a polycarbosilane resin, yellow to red-brown in color, which was soluble in aromatic and in chlorinated hydrocarbons. Such resins could be melt-spun but required a cure-step to render them infusible before they were pyrolyzed to ceramic... 

The first useful organosilicon preceramic polymer, a silicon carbide fiber precursor, was developed by S. Yajima and his coworkers at Tohoku University in Japan [5]. As might be expected on the basis of the 2 C/l Si ratio of the (CH3)2SiCl2 starting material used in this process, the ceramic fibers contain free carbon as well as silicon carbide. A typical analysis [5] showed a composition 1 SiC/0.78 C/0.22 Si02- (The latter is introduced in the oxidative cure step of the polycarbosilane fiber). 

In the vulcanisation of thick rubber articles the temperature may be stepped up in stages to ensure adequate heat penetration to the interior before the external surface begins to cure. Such a cure schedule is termed a step cure. Step post cures are used with thick section rubber articles to ensure that volatiles are released gradually without causing damage, such as porosity, due to an over rapid release. 

Additionally, if the salt bond reacts to form an amide bond during the curing step of the precursor, crosslinked networks can result due to diamide formation. An elegant solution to this dilemma can be realized by utilizing silylated amines... 

Coalescence of the film coating (determined by means of assessing drug release characteristics before and after imposition of a curing step)... 

Polyethylene in solution is treated with chlorine and sulfur dioxide to introduce approximately 1.39k sulfur and 29% chlorine into the polymer. Most of the chlorine is attached directly to the carbon atoms in the backbone of the polymer, The remainder is in the form of sulfuryl chloride groups, SO CI, through which crosslinking occurs In the curing step with metal oxides. The material has good oxidation and ozone resistance and thus overall excellent weather resistance. Calendered stocks are used for lining ditches and ponds, for example. 

The first step in preparing the very useful elastomer Hypalon involves treating a mixture of long-chain alkanes, H(CH2) H, where n =50-200, with sulfuryl chloride (S02C 2) in the presence of substances that can initiate radical-chain chlorination, as described in Section 4-5B. The product molecules contain many C-CI bonds and a few C-S02-Cl bonds, the latter of which are subsequently used in a curing step to improve the physical properties. How can the chain mechanism for chlorination with S02CI2 be modified to account for the formation of C-S02-Cl bonds ... 

Rigid composites are obtained by mixing graphite powder with a non-conducting polymeric matrix into a soft paste that becomes rigid after a curing step [52,53]. They could be classified according to the nature of the binder or the polymeric matrix into epoxy composites, methacrylate composites or silicone composites. 

Covalent bond formation is not an immediate process. Silane coating layers consist of physisorbed as well as chemisorbed molecules. Physisorbed molecules go into condensation only slowly and chemical stabilization of the coating layer requires a post-reaction curing step. In this step the modified substrate is thermally treated at temperatures generally in the 353 - 473 K range. 

A correlation of data from literature is often hampered by the use of different reaction parameters or silica types. Therefore, a clear survey of the effect of parameters related to reaction conditions and substrate structure is given. Furthermore, a full description of the modification mechanism is only possible if the processes occurring in the loading step and the curing step are discussed separately. The study of each of these steps requires dedicated analytical procedures. For the study of the loading step, most analyses are performed on the silane/solvent mixture, while spectroscopic analyses are performed on the modified substrate after drying and curing. 

The correlation of data from literature is often hampered by the different reaction conditions and types of silica used in various studies. In order to overcome this problem, the effect of the porosity of the substrate on the reaction mechanism is studied. Also here a difference has to be made between the effect in the loading and curing step. 

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