+ Epoxy Systems for Improved Thermal and Aging Stability
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Macromol. Symp. 2016, 365, 239–245 DOI: 10.1002/masy.201650023 | 239 Modification of Poly(Vinyl Chloride) Epoxy Systems for Improved Thermal and Agingþ Stability Bogdana Bashta,*1,2 Witold Brostow,*2 Gregory Granowski,2 Nathalie Hnatchuk2 Summary: Functional oligomers were synthesized via a reaction of ED-24 epoxy resin or a peroxy derivative of that resin with free peroxy and epoxy groups with adipic acid and via interaction between derivative of pyromellitic dianhydride and peroxy derivative of the same resin in the presence of benzyl triethylammonium chloride. The effects of oligomer presence, oligomer nature and amount on the crosslinking of poly(vinyl chloride) (PVC) mixtures were investigated. The thermal stability of synthesized oligomers and PVC mixtures based on them were determined, as was resistance to aging. Schematics of cross-linking reactions of modified mixtures are proposed. Higher thermal stability and better resistance to aging have been achieved. Keywords: aging stability; cross-linking; functional oligomers; poly(vinyl chloride); thermogravimetric analysis (TGA) Introduction cross-linked structure contributes to the improvement of the thermal stability of Polyvinyl chloride (PVC) is one of the most PVC, what in turn greatly increases its range widely produced polymers. Global produc- of applications. Crosslinking can be achieved tion of PVC resins is estimated as about by introduction of epoxy resins. 50 million tons/year.[1] Approximately 70 % The stability can be conferred by of this amount are consumed by China, opening of the epoxy rings and consequent North America and Western European stabilization of labile chlorine atoms, countries. PVC can be considered one of avoiding the generation of HCl created the most versatile plastics, with high flexibil- during the degradation of the chain. ity or stiffness by incorporating additives to We created PVC mixtures by incorpo- meet a wide range of properties, depending rating chemical modifiers such as poly- on the application.[2] Among the various functional epoxy resins in the presence or types of PVC compounds, plastisols and without an amino accelerator. We evalu- organosols are among the most versatile, as ated the effects of the functional epoxy they offer several possibilities that yield new resins and amino hardener content on the products. The technology used to obtain crosslinking process of PVC mixtures. Our these materials includes a large variety of objectives were improvement of thermal molding and coating processes.[3] Karmalm stability and mitigation of aging. and his colleagues[4] reported that forming a Experimental Section 1 Department of Polymer Chemistry & Technology, Lvivska Polytechnika National University, 12, St. Bandera Street, 79013 Lviv, Ukraine Materials E-mail: [email protected] The PVC grade is called SE1300 N provided 2 Department of Materials Science & Engineering, by Shintech Inc, Houston, TX, USA, and was University of North Texas, 3940 North Elm Street, Denton, TX 76207, USA used as the main polymer matrix. It contains E-mail: [email protected] vinyl chloride monomer up to 10 ppm by ß 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 240 | Macromol. Symp. 2016, 365, 239–245 weight and was used without further purifi- CPO has M 560 g/mol, X 8.8 %, n ¼ COOH ¼ cation. Thermal stabilization of formulation e.n. 0%,andО 2.0 %. ¼ аct. ¼ was achieved by incorporating a Ca/Zn PCOS was synthesized in accordance commercial salt. As plasticizer we have used to the method described in,[8] with the ditridecyl phthalate (DTDP) and triisononyl formula: trimellitate (TINTM) at the 2:3 ratio. PCOS has M 1890 g/mol, X n ¼ COOH ¼ AsmodifiersofPVCmixtures,weapplied 6.5 %, e.n. 0 %, and Оаct. 1.4 %. ¼ ¼ an epoxy resin mixture of diglycidyl ether As the crosslinking agent, we have used of bisphenol A (70–80 %) and alkylglycidyl polyethylene polyamine (typically used in ether (20–30 %) and also oligomers with the chemical industry) (PEPA), with the carboxy and epoxy (CDER), peroxy and formula: epoxy (PO), peroxy and carboxy (CPO) or carboxy, peroxy and secondary hydroxyl (PCOS) functional groups. CDER is a carboxy derivative of ED-24 epoxy resin; it was synthesized in accor- dance to a method described in,[5] leading The mechanism usually accepted for to the formula: the crosslinking process of epoxy resins involves a reaction with amines: CDER has the molecular mass М n ¼ 450 g/mol, the carboxy groups content X 8.6 % and the epoxy number COOH ¼ Preparation of PVC Samples e.n. 7.9 %. fi ¼ At rst PVC powder was mixed with 1.0 % PO is a peroxy derivative of ED-24 Ca/Zn powder. Then a functional oligomer epoxy resin; it was synthesized as described and PEPA were dissolved in the plasticizer. [6] in, with the formula: After that, the organic solution was added to the mixture of PVC with Ca/Zn. All components were mixed at room tempera- ture; then the homogeneous composition was filled into a steel mold for 20 samples PO has M 420 g/mol, e.n. 9.0 %, with dimensions of 20Ã20Ã2 mm. Compres- n ¼ ¼ and active oxygen content О 2.9 %. sion molding process was carried out at аct. ¼ CPO is the carboxy derivative of PO 150 C and consisted of heating for 10 min was synthesized in accordance to method[7] before applying 3 cycles of 10 metric tons with the formula: of pressure for 2.5 min. Afterwards the pressure was released and the samples were cooled to the room temperature in 15 min. ß 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ms-journal.de Macromol. Symp. 2016, 365, 239–245 | 241 Figure 1. Thermogravimetric diagrams of several oligomers: PCOS (а), CDER (b), CPO (c) and PО (d). Thermogravimetric Analysis (TGA) The results are presented in Figure 1 and Thermal stability of all compositions was the respective numerical values reported in determined by TGA 7 machine from Perkin Table 1. The beginning of a weight loss Elmer, USA. The TGA technique is well period is defined by the loss of 0.5 % of the described by Menard,[9] Lucas and her original or previous weight. The end of a colleagues[10] or Gedde.[11] The measure- weight loss period is defined similarly, that ments were performed under nitrogen gas is changes in weight not exceeding 0.5 %. (commercial grade). The heating rates varied The second number pertaining to the end between 5 and 20 C/min. The maximum of a weight loss period provides the total temperature was 900 K. We have also consid- weight loss for that period. Thus, for instance ered DTG curves (first derivatives of TGA 743/85 means that at the temperature of curves), which describe the weight loss rate 743 K the total weight loss since the begin- (dm/dT) where m is the mass. ning of the run amounts to 85 %. We find that the most thermostable Aging Stability Investigation oligomer is CDER, with the highest begin- Aging stability of all compositions was ning temperature of the first region of determined by samples’ weight loss. The weight loss equal to 433 K; it is well stable samples obtained after compression mold- until 620 К or so; it can be used in polymeric ing process were kept in a thermal chamber at 422 K for 7 days. Every day all the Table 1. samples were weighed and the percentage Thermal stability of functional epoxides. of weight loss calculated. Weight loss temperature/К and amount/% The first period of The second period TGA Results weight loss of weight loss Oligomer Beginning End Beginning End Modifying Agents PCOS 393 743/85 743 949/90 Given our objectives, it was necessary to CDER 433 773/78 773 949/88 assure thermal stability of our additives. The CPO 403 763/85 763 873/89 technique used has been described above. PО 373 430/63 463 873/85 ß 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ms-journal.de 242 | Macromol. Symp. 2016, 365, 239–245 mixtures for creation of thermostable mate- (Figure 2b) we find it at 609 K. The second rials. Oligomers PCOS and CPO which peaks for these two compositions are closer contain in their structures labile –О–О– (763 and 769 K, respectively). Pure PVC bonds can be used in polymeric mixtures as powder starts to degrade at 573 К (Figure 2a) sources of free radicals. The formation of but mixture ІІ at 543 К. When we add the the radicals takes place by decomposition epoxy resin to the mixture (mixture III), of –О–О– bonds. Our results confirm the we observe a further reduction of the presence of –О–О– bonds in the molecules degradation peak until 598 K (Figure 2c). of synthesized PCOS and CPO oligomers. Simultaneously, the second peak remains Further, CDER contains oxirane groups almost the same (766 K). At the same time which can undergo radical formation lead- we observe increasing temperature of the ing to cross-linking. PO is similar to CDER beginning of degradation of the mixture in this respect, while it contains oxirane as with epoxy resin in the amount 2.5 mass well as peroxy groups. parts (mixture III) (548 K) as compared with the beginning of degradation for the PVC Mixtures mixture PVC plasticizer (533 K) (mixture þ For preparing of PVC mixtures we use the II) (Figure 2c and 2b and Table 3). PVC powder, the Ca/Zn thermal stabilizer, Adding to the mixture the crosslinking and a mixture of plasticizers: ditridecyl agent PEPA (mixture IV and mixtures VI À phthalate (DTDP) and triisononyl trimel- IX) results in lower beginning degradation litate (TINTM) in the 2:3 ratio. We have temperatures in comparison to the control used PCOS, CDER, CPO and PO as sample I; closest to that control sample is modification agents.