Soluble nylon cross-linking

The general rule that like dissolves like bolds weU with pofymers for example, polymers absorb considerable quantities of their own monomers. If the polymer is linear it may well completely dissolve in its own monomer or other good solvent. If the solubility is lower, then the potymer, when immersed in solvent, will absorb in equilibriuin a fraction of its own mass and will not dissolve the lower the solubQity the lower the fraction. In 1.N.9 the equilibrium water contents of nylons are given for 50% and 100% RH. Hiis is the behaviour observed for vapours equilibrium absorption increases with vapour pressure. The absorbed molecules are absorbed only into the amorphous fraction of ctystalline potymers such as the nylons. Cross-linking in rubbers lowers the absorption the swelling of the network is impeded Ity the cross-links. As the network expands because of the absorption of diluent, the entropy forces between tie points increase (Figures 3.3 and 3.4) and this limits the swelling. 

Some commercial durable antistatic finishes have been Hsted in Table 3 (98). Early patents suggest that amino resins (qv) can impart both antisHp and antistatic properties to nylon, acryUc, and polyester fabrics. CycHc polyurethanes, water-soluble amine salts cross-linked with styrene, and water-soluble amine salts of sulfonated polystyrene have been claimed to confer durable antistatic protection. Later patents included dibydroxyethyl sulfone [2580-77-0] hydroxyalkylated cellulose or starch, poly(vinyl alcohol) [9002-86-2] cross-linked with dimethylolethylene urea, chlorotria2ine derivatives, and epoxy-based products. Other patents claim the use of various acryUc polymers and copolymers. Essentially, durable antistats are polyelectrolytes, and the majority of usehil products involve variations of cross-linked polyamines containing polyethoxy segments (92,99—101). 

Furthermore, crystalline polymers do obey the rules even at room temperature in so far as swelling behaviour is concerned. This again is a demonstration that crystalline regions serve as physical cross-links. Some crystalline polymers with strong hydrogen bonding groups can be made to dissolve at room temperature. But in these cases a very specific interaction between polymer and solvent must occur. For example, cellulose is soluble in 70% sulphuric acid and in aqueous ammonium thiocyanate nylon 6.6 is soluble in phenol and in a 15% calcium chloride solution in methanol. 

Hexafluoroisopropanol is able to dissolve most polyesters and polyamides (nylons) at room temperature in about 4-8 h. Sodium trifluoroacetate (NAT-FAT) is typically added to suppress any polyelectrolyte effects that could occur in HFIP [9]. GPC columns made from cross-linked polystyrene-divinylbenzene are typically used to perform the separation [14]. Calibration is generally performed using poly(methyl methacrylate) standards instead of polystyrene standards, due to solubility constraints [5,15]. 

According to Grattan (9), the most common polymers used in solvent-resin consolidant systems are acrylics, poly(vinyl acetates), poly(vinyl butyrals), and soluble nylon. Of these, soluble nylon has since been shown to be unsuitable because it inevitably cross-links and embrittles within as little time as a few weeks (iO). The others are known to have excellent longterm stability (9). Most likely the stability of polymers placed inside the wood may be even better, because they would be protected from light-catalyzed degradation reactions. Possible wood-polymer interactions, however, are unknown at this time. 

Methylmethoxy nylons in which about 33% of the amide groups have been substituted are commercially available. Such polymers are soluble in alcohols and may be cross-linked by heating at about 120°C in the presence of an acid... 

Many polymers are used in contact with water. The conditions may be made more extreme by heating the water (but see above), by changing the pH or dissolved salts, or by using alternating wet/dry periods. Polymers that react with water, often by hydrolysis, will be sensitive to changes in pH. A notable example reported in conservation is the cross-linking of soluble nylon in even mildly acidic conditions (Bockhoff et al., 1984). 

Various polymers have been successfully electrospun from solution, sol-gel suspension, or melt into ultrafine nanotibers. For example, as listed in Table 13.2, these polymers included nylon-6 [20, 21], polyacrylonitrile (PAN) [22, 23], polyethylene terephthalate (PET) [24], polyvinyl alcohol (PVA) [25], polystyrene (PS) [26, 27], polyvinylidene fluoride (PVDF) [28, 29], polyethersulfone (PES) [30], polyimides (PI) [31, 32], polyethylene oxide (PEO) [33], polyurethanes (PU) [34], polycarbonates (PC) [35], polycaprolactone (PCL) [36], polybenzimidazole (PBI) [37, 38], polyvinylpyrrolidone (PVP) [39], polytrimethylene terephthalate (PTT) [40], polyvinyl chloride (PVC) [41], polymethylmethacrylate (PMMA) [42], hydrox-ypropyl cellulose (HPC) [43], polyglycolic acid (PGA) [44], polyhydroxybutyrate (PHB) [45], cellulose acetate (CA) [46,47] and many more. To be used as filtration membranes, nanoflbers made of water-soluble polymers have to be further cross-linked after the electrospinning process. As polymers having different physical and... 

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