ROSIN POLYMER

Liu X and Zhang J (2010), High-performance biobased epoxy derived from rosin , Polym Int 59, 607-609. DOI 10.1002/pi.2781. 

Characteristic IR absorption bands of PAI-l(Fig.4), PAI-2 (Fig. 5.) and PAI-3 (Fig. 6) were observed near 1785 cm , 1715 cm and 725 cm"l due to imide groups and near 1630 cm" and 1530 cm" due to amide groups. Because of the complex structure of the polymer, characteristic IR bands observed were not so sharp due to overlapping of different bands of various chromophore groups present in the rosin polymer molecule. 

We have found that RMA appears to be a suitable substitute for TMA as a raw material for polymers. Rosin polymers such as polyeste-rimides via RMA or RMID or its derivative possess similar solubility and other characteristics to those synthesized from TMA. The thermal behavior of a polyesterimide (PEI-2) from rosin has been compared with that of TMA-based polyesterimides (Table 4). It is found from Table 4 that the thermal stability of the polyesterimide from RMA is similar to that of TMA. The glass transition temperature,... 

Tg, of PEI-2 is 180 C, which is also similar to the Tg s of polymers from TMA. Rosin polymers may, therefore, be regarded as a new class of processable heat resistant polymer from a renewable resource. 

The rosin moiety of the polymer, polyesterimides and polyamidei-mides alike, offers interesting possibilities which may be explored further. One such possibility is the utilization of the residual unsaturation in the hydrophenanthrene ring structure of the rosin moiety. Although this unsaturation site is sterically very much hindered and therefore stable, attempts may be made to exploit it for crosslinking or other reactions by free radical processes. If this is successful, rosin polymers may be used for fabrication of void-free high temperature laminates and composites with suitable formulation. 

Rosin is compatible with many materials because of its polar functionaUty, cycloaUphatic stmcture, and its low molecular weight. It has an acid number of ca 165 and a saponification number of ca 170. It is soluble in aUphatic, aromatic, and chlorinated hydrocarbons, as well as esters and ethers. Because of its solubiUty and compatibiUty characteristics, it is useful for modifying the properties of many polymers. 

Rosin ester resins are used extensively in pressure-sensitive adhesives as tackifiers. The adhesive is formulated by blending the resin with a polymer in solution or as aqueous emulsions. Typical compositions may contain about 50% resin. The glycerol or pentaerythritol esters of stabilized rosins are often used because they are stable on aging. 

Rosin, modified rosins, and derivatives are used in hot-melt adhesives. They are based primarily on ethylene—vinyl acetate copolymers. The rosin derivative is used in approximately a 1 1 1 concentration with the polymer and a wax. The resin provides specific adhesion to the substrates and reduces the viscosity at elevated temperatures, allowing the adhesive to be appHed as a molten material. 

Rosin ester resins are used as modifiers in the formulation of chewing gum. The rosin derivative modifies the physical properties of the polymer used, providing the desired masticatory properties. The glycerol ester of hydrogenated rosin is the predominant choice, because stabilized materials have improved aging resistance, which extends the shelf life of the gum. 

The most commonly used emulsifiers are sodium, potassium, or ammonium salts of oleic acid, stearic acid, or rosin acids, or disproportionate rosin acids, either singly or in mixture. An aLkylsulfate or aLkylarenesulfonate can also be used or be present as a stabilizer. A useful stabilizer of this class is the condensation product of formaldehyde with the sodium salt of P-naphthalenesulfonic acid. AH these primary emulsifiers and stabilizers are anionic and on adsorption they confer a negative charge to the polymer particles. Latices stabilized with cationic or nonionic surfactants have been developed for special apphcations. Despite the high concentration of emulsifiers in most synthetic latices, only a small proportion is present in the aqueous phase nearly all of it is adsorbed on the polymer particles. 

Eatty acid soap was first used for ESBR. Its scarcity prompted the investigation of rosin acids from gum and wood as substitutes (1). The discovery of the disproportionation of rosin allowed rosin acid soaps to overcome the polymerization inhibition of untreated rosin acids. Rosin acid soaps gave the added benefit of tack to the finished polymer. In the 1990s, both fatty acid and rosin acid soaps, mainly derived from tall oil, are used in ESBR. 

Tackifiers are used to increase the tackiness and the setting speed of adhesives. They increase tackiness by softening the poly(vinyl acetate) polymer in the wet and the dry adhesive film. Tackifiers are usually rosin or its derivatives or phenoHc resins. Other additives frequently needed for specific apphcation and service conditions are antifoams, biocides, wetting agents, and humectants. 

Monomer conversion (79) is followed by measuring the specific gravity of the emulsion. The polymerization is stopped at 91% conversion (sp gr 1.069) by adding a xylene solution of tetraethylthiuram disulfide. The emulsion is cooled to 20°C and aged at this temperature for about 8 hours to peptize the polymer. During this process, the disulfide reacts with and cleaves polysulfide chain segments. Thiuram disulfide also serves to retard formation of gel polymer in the finished dry product. After aging, the alkaline latex is acidified to pH 5.5—5.8 with 10% acetic acid. This effectively stops the peptization reaction and neutralizes the rosin soap (80). 

Latex Types. Latexes are differentiated both by the nature of the coUoidal system and by the type of polymer present. Nearly aU of the coUoidal systems are similar to those used in the manufacture of dry types. That is, they are anionic and contain either a sodium or potassium salt of a rosin acid or derivative. In addition, they may also contain a strong acid soap to provide additional stabUity. Those having polymer soUds around 60% contain a very finely tuned soap system to avoid excessive emulsion viscosity during polymeri2ation (162—164). Du Pont also offers a carboxylated nonionic latex stabili2ed with poly(vinyl alcohol). This latex type is especiaUy resistant to flocculation by electrolytes, heat, and mechanical shear, surviving conditions which would easUy flocculate ionic latexes. The differences between anionic and nonionic latexes are outlined in Table 11. 

Rosin and its derivates have shown wide compatibility with a broad range of acrylics and other PSA polymer precursors. This property has made them one of the most common tackifiers in the industry. 

Adhesion depends on a number of factors. Good adhesion is defined by most customers as substrate failure. The major adhesive manufacturers possess equipment that allows them to make bonds with customer substrates under conditions that closely simulate actual packaging lines. These bonds are peeled either automatically or by hand to gauge adhesion. The most important factors influencing adhesion are the wet-out of the substrate, partieularly by the polymer component of the adhesive system, and the specific adhesion with the substrate. Choice of resin is critical for both. Rosin, rosin esters and terpene phenolics are eommonly added for these purposes in EVA and EnBA-based systems. Adhesion at low temperatures is also influenced by the overall toughness of the system at the test temperature. 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

AKDs are waxy, water-insoluble solids with melting points around 50 °C, and ASAs are viscous water-insoluble liquids at room temperature. It is necessary to prepare them as stabilised emulsions by dispersion in a cationic polymer (normally cationic starch). Small amounts of retention aid and surfactants may also be present. Particle size distributions are around 1 fim, and addition levels around 0.1% (of pure AKD or ASA) by weight of dry fibre. This is an order of magnitude lower than the amount of rosin used in rosin-alum sizing (1-2%). Emulsions of AKD are more hydrolytically stable than ASA, and the latter must be emulsified on-site and used within a few hours. 

As in the case of rosin sizing, the first step is to retain the emulsified size particle in the wet web. The mechanism of retention is probably by heterocoagulation of the cationic size particles to the negatively charged fibre surface. The charge characteristics of the stabilising polymer become important as demonstrated by the effect of pH on the retention of AKD emulsion particles stabilised with a tertiary cationic starch (Figure 7.17). 

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