Polymer Degradation and Stability (v.81, #1)

In this study, titanium alkoxide catalyst dependences of condensation polymerization, thermal degradation and stability were examined for a biodegradable aliphatic poly(tetramethylene succinate) (PTMS). A series of aliphatic PTMSs were synthesized through polycondensation of 1,4-butanediol and succinic acid in bulk with various amounts of titanium tetraisopropoxide (TTiPO) as the catalyst, and were further characterized by gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. To reveal the presence and effect of catalyst residues, the crude product PTMS samples were precipitated in methanol from their chloroform solution, and were further refluxed in an acid solution to selectively hydrolyse the weak metal alkoxide moieties formed. Results of GPC analysis indicated that the original precipitated polyesters exhibited remarkably increasing molecular weights with a decrease in the catalyst/succinic acid feed molar ratio, and strong catalyst dependence of molecular weight and distribution were detected for the product polyesters. As for the acid deactivated samples, it was found that the higher the catalyst concentration used for polyester synthesis, the more remarkable was the decrease in molecular weight observed as compared with the corresponding original precipitated polyesters. Hence, a weak chain linker structure, such as (RO) n Ti(OP) m with m> 1 was reasonably suggested to be included in the macromolecular architecture of polyester, where RO and P respectively express the alkoxyl moiety and polyester chain. Thermal analysis showed similar melting points and glass transition temperatures for all polyester samples. In contrast, a strong catalyst dependence of thermal degradation and stability was found for the TTiPO catalysed polyesters, and can be interpreted for the formed weak (RO) n Ti(OP) m structures.
Keywords: Biodegradable aliphatic PTMS; TTiPO catalyst; Condensation polymerisation; Thermal stability;

Antioxidant properties of lignin in polypropylene by C. Pouteau; P. Dole; B. Cathala; L. Averous; N. Boquillon (9-18).
The non-linear relation between Kraft lignin activity and its concentration in the blend has been explained by molecular weight polydispersity, and correlated to activities of Kraft fractions.
Keywords: Polypropylene; Antioxidant; Ageing; Lignin; Solubility;

New formulations of waterborne polyurethanes (wPU) and poly(urethane-urea)s (wPUU) were produced based on hydroxy-terminated polybutadiene (HTPB), poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), and three different types of aliphatic diisocyanates—isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (HMDI) and hexamethylene diisocyanate (HDI)—and the aromatic tolylene diisocyanate (TDI). Three types of chain extender were used in some of the formulations: ethylene glycol (EG), forming polyurethanes, and hydrazine (HYD) or ethylenediamine (EDA), resulting in poly(urethane-urea)s. In the formulations, HTPB content and NCO/OH ratio were varied. The thermal stability of the materials, obtained as cast films prepared from aqueous dispersions was evaluated by thermogravimetry (TG). It was observed that initial degradation temperatures were above 200 °C, with two- or three-step degradation profiles. An increase in HTPB content, the presence of urea linkages, and HMDI as diisocyanate in the formulations led to materials with higher thermal stability. DTG curves exhibited stages not perceptible in the curves of weight loss, which were mainly influenced by the differences in the formulations.
Keywords: Polyurethanes; Aqueous dispersions; Hydroxyl-terminated polybutadiene; TG; DTG;

Many PVC materials deteriorate only 5 years after manufacture. The extent, rate and mechanisms of deterioration of model and naturally aged PVC containing di (2-ethylhexyl) phthalate (DEHP), have been examined during thermal ageing in various environments. Weight loss was used to quantify loss of DEHP, attenuated total reflection Fourier transform infrared spectroscopy to quantify concentration of DEHP at surfaces and optical densitometry to examine darkening of samples. The rate and extent of deterioration of plasticized PVC and the migration and loss of DEHP plasticizer were related. DEHP inhibited degradation of the PVC polymer, therefore when it was lost, discolouration, tackiness and embrittlement resulted. Less plasticized materials degraded more rapidly than those more highly plasticized. Degradation was inhibited in both model sheets and naturally aged materials by enclosing them in a non-adsorbent material such as glass, containing non-agitated air or storing them in a freezer.
Keywords: PVC; Plasticizer; Phthalate; ATR-FTIR; DEHP; Museum; Indoor climate;

Phenylurea and phenylthiourea derivatives have been investigated as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. The results reveal the higher stabilizing potency of the investigated organic stabilizers as compared with commercial reference stabilizers, which is proved by their greater induction period values, but with higher dehydrochlorination rate at the later stages of degradation. Complexation of these materials with the chlorides of Ni2+ and Cd2+ greatly improved the induction period values, however the dehydrochlorination rate is only slightly improved. On the other hand, blending the investigated thermal stabilizers with some of the commercially known reference stabilizers in different proportions leads to a true synergistic effect. The induction period values and the degradation rate were remarkably improved. A probable mechanism for the stabilizing action of phenylurea and phenylthiourea derivatives has been proposed.
Keywords: Poly(vinyl chloride); Thermal degradation; Stabilization; Organic stabilizers; Phenylurea and phenylthiourea derivatives;

Thermal degradation behavior of polyamide 6/clay nanocomposites by K.P Pramoda; Tianxi Liu; Zhehui Liu; Chaobin He; Hung-Jue Sue (47-56).
This paper focuses on the study of thermal degradation and evolved gas analysis using thermogravimetric analysis (TGA) coupled to Fourier transform infrared (FTIR) spectroscopy, i.e., TG–IR, to study polyamide 6 (PA6) and PA6-clay nanocomposites prepared by melt compounding. The thermal decomposition of PA6 and its clay nanocomposites takes place with the evolution of the cyclic monomer (caprolactam) first, followed by other volatile gases like CO2 and NH3, which are characterized by the presence of oligomeric products with nitrile and vinyl chain ends in the infrared (IR) spectra. The onset temperature for degradation is 12 °C higher for PA6 with 2.5 wt.% of clay loading than that for neat PA6, whereas, the onset temperature for degradation remained almost unchanged for samples with higher clay loading (i.e. 5, 7.5 and 10 wt.% clay). The above findings are related to the morphological observations that show an optimal exfoliated structure only for the nanocomposite with 2.5 wt.% clay, and distinct clay agglomeration in those with higher clay loadings. Our study suggests that only exfoliated polymer/clay nanocomposites exhibit improved thermal stability. Agglomerated clay particles do not significantly affect thermal stability of the polymer matrix. The activation energies for degradation, E a, estimated by Kissinger method, for PA6 and PA6–2.5 wt.% clay nanocomposite were found to be 175 and 199 kJ/mol in N2, and 228 and 223 kJ/mol in air, respectively.
Keywords: Polyamide 6; Clay; Nanocomposite; Thermal degradation;

This paper presents the results of thermal analysis (TA) with simultaneous mass spectroscopy and FTIR investigations of Y–Ba–Cu-polymer and Bi–Sr–Ca–Cu-polymer precursors where the polymers are either novolak or poly(acrylic acid) (PAA). It is shown that the thermal degradation behaviour of precursors influences the quality of high temperature superconductor (HTSC) films, which were characterized by electrical measurements for determination of transition temperature and critical current density.
Keywords: Thermal degradation; Polymer precursor; High temperature superconductor preparation;

In vitro degradation behaviour of biodegradable soy plastics: effects of crosslinking with glyoxal and thermal treatment by Cláudia M. Vaz; Leontine A. de Graaf; Rui L. Reis; António M. Cunha (65-74).
In-vitro degradation of soy-derived protein materials, non-crosslinked (SItp), crosslinked with glyoxal (X-SItp) or submitted to heat treatment (24TT-SItp), was studied with either an isotonic saline solution without enzymatic activity or containing bacterial collagenase. The changes in weight of the samples during the in-vitro degradation were studied and compared with the variations of the mechanical properties. The weight loss of SItp, X-SItp and 24TT-SItp were more pronounced when using collagenase. After 24 h of immersion, SItp lost 10.6% of its initial weight whereas 0.6X-SItp and 24TT-SItp lost 1.7 and 5.7%, respectively. In every case, the weight loss was found to be directly proportional to the respective crosslinking degree: 2.4% for SItp, 44% for 0.6X-SItp and 27.8% for 24TT-SItp. Consequently, the susceptibility of the soy materials towards enzymatic degradation could be controlled by varying the degree of crosslinking of the samples. The mechanical properties proved to be more sensitive to the loss of plasticiser (glycerol) during immersion than to the degradation of the polymeric matrices. After 24 h of immersion all the materials presented an increase in stiffness and brittleness due to the complete leaching of glycerol from the matrices. SItp, X-SItp and 24TT-SItp proved to be suitable materials for either load-bearing applications or temporary applications such as tissue engineering scaffolds or drug delivery systems.
Keywords: Soy; Soy-derived protein material; Crosslinking; Mechanical properties; In-vitro degradation;

Electron and proton irradiation of poly(vinylidene fluoride): characterization by electron paramagnetic resonance by E. Adem; G. Burillo; E. Muñoz; J. Rickards; L. Cota; M. Avalos-Borja (75-79).
Films of poly(vinylidene fluoride) (PVDF) were exposed to proton and electron beam irradiation at high doses, from 50 to 5000 kGy. Modifications induced in the samples were determined by electron paramagnetic resonance (EPR). Samples irradiated with electrons and protons showed similar behaviours, with the presence of several types of radicals. The number of radicals produced as a function of dose in the proton case is slightly below that of the electron case, indicating non-linear effects. The evolution of radical density and its decay in the dark and in normal light conditions at room temperature was studied, as well as its decay with increase in temperature. When kept in the dark for up to 180 days, no decay of radicals was observed.
Keywords: PVDF; Radiation; Electrons; Protons; EPR;

Microcalorimetry (MC) and chemiluminescence (CL) measurements have been used to study the oxidation of unstabilised polypropylene (PP) particles. The oxidation profiles obtained by the two techniques were found to be similar although a time shift between the profiles was observed, particularly at low temperatures. The similar shape suggests a close relation between the rate of the overall oxidation process as measured by MC and the rate of the CL emitting reactions. MC revealed that the energy evolved up to the maximum of the MC oxidation profile increased significantly above 110 °C indicating a change in the overall oxidation process, possibly associated with a more pronounced secondary oxidation. The results indicate that above 110 °C the maximum of an oxidation profiles (as measured either by MC or CL techniques) is not suitable for evaluating the temperature dependency of oxidation. FTIR was used to follow the formation of oxidation products. It was found that the oxidation profiles obtained by either MC or CL measurements did not reflect the carbonyl build-up but more likely the hydroperoxide build-up.
Keywords: Polypropylene; Oxidation; Degradation; Stability; Heat flow; Calorimetry; Microcalorimetry; Chemiluminescence; CL; Kinetic; 2277 TAM; Thermal activity monitor;

Thermal and catalytic degradation of poly(propylene)(PP)/poly(vinyl chloride)(PVC) at 380 °C, poly(ethylene)(PE)/PVC at 420 °C, and poly(styrene)(PS)/PVC at 360 °C into oil was carried out under atmospheric pressure by semibatch operation. The purpose of this study is to determine the boiling-point distribution of the products of the degradation of PVC mixed plastics and to remove chorine compounds from products with suitable sorbents. In the catalytic degradations, the Al–Zn composite catalyst was tested as both cracking and dechlorination catalyst. Compared to thermal degradation, the catalyst accelerated the degradation rate of polymers and lowered the boiling point of liquid products, and at the same time, it showed good effect on the fixation of evolved HCl and significantly decreased the chlorine content in the oil.
Keywords: PVC; Thermal degradation; Al–Zn composite catalyst; Dechlorination; Mixed plastics;

(2-Hydroxy-3-phenoxy)propyl methacrylate (PPMA) and (2-hydroxy-3-tetrahydrofurfuryloxy)propyl methacrylate (THPMA) were polymerised using benzoyl peroxide as initiator in 1,4-dioxane at 60 °C. The polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), IR, 1H and 13C NMR techniques. The thermal degradations of poly(THPMA) and poly(PPMA) were investigated by thermogravimetric analysis (TGA) and programmed heating of the polymers from ambient to 500 °C under vacuum, followed by product collection, and using IR spectra of partially degraded polymer. IR, GC–MS, 1H and 13C NMR techniques were used in product identification studies. Although the heating of poly(THPMA) to 330 °C gives the monomer in ratio 87.0%, it gives the monomer in ratio 47.7% between 330 and 500 °C, whereas poly(PPMA) gives the monomer in ratio 85.9% during heating from ambient to 500 °C. Activation energies of the degradations given the corresponding monomers in ratio 85% at least, and the mechanism of degradation given some other major products, are discussed.
Keywords: Methacrylate; Hydroxy and alkoxy (phenoxy) side chain; Thermal degradation;

The long-term weathering behavior of UV curable clearcoats by C.M. Seubert; M.E. Nichols; V.A. Cooper; J.L. Gerlock (103-115).
The long-term weathering behavior of two UV cure clearcoat systems, one a monocure, the other a dual cure system, was studied by infrared spectroscopy, UV spectroscopy, Raman spectroscopy, dynamic mechanical thermal analysis (DMTA), and fracture energy measurements. The photooxidation rate and consumption of residual acrylate double bonds during weathering was highly dependant on the presence of hindered amine light stabilizers (HALS) for both systems. Ultraviolet light absorbers (UVA) had little effect on the photooxidation rate or rate of consumption of acrylate double bonds during weathering. Changes in fracture energy (brittleness) of the clearcoats mirrored the changes found in the consumption of residual acrylate double bonds. DMTA analysis of both clearcoats indicated no increase in crosslink density as weathering progressed, suggesting the acrylate double bonds were not reacting to form additional crosslinks.
Keywords: UV curable clearcoats; Weathering; Photooxidation;

Polyvinyl alcohol(PVA)–Pt/TiO2 composite nanofiber aggregate was prepared by electrospinning method and the photocatalytic degradation of solid-phase PVA was investigated. The experimental results showed that the 150–350 nm PVA–Pt/TiO2 composite fiber could be obtained from the PVA–Pt/TiO2 sol-like system by the electrospinning method and the photocatalytic technique was effective for the degradation of solid-phase PVA in this fiber. The weight loss of PVA depended on the wavelength of UV light and the irradiation time; it reached 78.5 and 40.2%, respectively under average 250 and 360 nm UV light irradiation for 16 h. The degradation rate of PVA in composite fiber was higher than that in composite film under identical conditions. The samples were characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Ultraviolet–visible diffuse reflectance spectroscopy (UV–vis) and Fourier transform infrared (FT–IR) techniques. The possible mechanism of PVA degradation was also discussed in this paper.
Keywords: Polyvinyl alcohol; Nanosize fiber; Photocatalytic degradation; Pt/TiO2 photocatalyst;

Calculation of activation energy from fraction of bonds broken for thermal degradation of polyethylene by Zhiming Gao; Iwao Amasaki; Tsuyoshi Kaneko; Masahiro Nakada (125-130).
The fraction of bonds broken in thermal degradation of polyethylene was estimated. Activation energy of the degradation was then calculated from the fraction of bonds broken. It was found that the activation energy thus obtained is close to the values for β C–C bond scissions and β C–H bond scissions of hydrocarbon radicals. β C–H bond scission of radicals is proposed as part of the mechanism of thermal degradation of polyethylene, which provides an understanding of detail of hydrogen transfer in the polymer melt and provides a route for hydrogen gas formation in pyrolysis of polyethylene.
Keywords: Fraction of bonds broken; Beta scission; Boiling point; Activation energy; Polyethylene;

Morphological changes of lath-shaped single crystals of poly[(R)-3-hydroxybutyrate] (P(3HB)) during annealing were followed in situ by a temperature-controlled atomic force microscopy (TC-AFM) in order to elucidate thermal stability or chain-mobility within the individual single crystal. Two kinds of the solution-grown single crystals prepared under different crystallization conditions were used to also investigate the influence of crystallization temperature on the annealing behavior. The significant morphological changes during annealing were observed at temperatures above the original crystallization temperature. The TC-AFM observations have revealed that ridges on the lamellar surface running across the crystal width (parallel to the b-axis), and cracks along the long axis of the crystal (parallel to the a-axis) are occasionally formed by thermal treatment. At a higher annealing temperature, numerous notches along the b-axis were frequently formed at the lateral sides of crystal. The notch formation may be due to preferential melting of the defective or less perfect regions within the lamellar crystal. The whole crystal became narrow while the notches progressed along b-axis, and some cavities developed at the central portion of the crystal as annealing temperature was elevated. The isothermal annealing experiment has demonstrated that the melting of P(3HB) crystals gradually progresses from the lateral outer faces. On the basis of the results, it has been concluded that the less perfect regions along the a-axis and b-axis exist within the P(3HB) single crystal, and that melting of the regions at the lateral sides of crystal is more easily initiated.
Keywords: Poly[(R)-3-hydroxybutyrate]; Single crystal; Annealing; Melting; In situ AFM;

Morphology and the biomechanical properties of the fibrous nonwoven poly (glycolic acid) (PGA) scaffolds were studied over 8 weeks of in vitro degradation. Morphology of the PGA scaffold was examined using scanning electron microscopy (SEM). Results showed that at day 3 to day 14, the fibers in the scaffolds became more separated apparently due to the initial swelling effect of medium absorption. However, the samples shrank dimensionally by day 28 and some became disintegrated shortly afterwards. More fiber endings could apparently be found in samples with longer periods of degradation. As degradation time increased, some fiber end surfaces showed signs of further decays. During the degradation period, there were little changes in the chemical structures as determined by Fourier Transform Infrared Spectroscopy. Thermal studies by differential scanning calorimetry (DSC) showed that the melting temperatures of the scaffold material shifted lower, while the degree of crystallinity determined by both DSC and X-ray diffraction increased significantly during the initial degradation period and apparently decreased afterwards. Biomechanical tests of 10% compression and 14% shear were performed to study the structural properties of the scaffolds upon degradation. The results clearly showed that the fibrous non-woven PGA scaffolds lost their structural properties substantially over relatively short period of in-vitro degradation. Whether such a degradation speed is optimal or not should be carefully evaluated for different tissue engineering applications.
Keywords: Poly(glycolic acid); Scaffolds; Degradation; Morphology; Biomechanical properties;

A phenolic antioxidant trapping both alkyl and peroxy radicals by Yasukazu Ohkatsu; Takanori Matsuura; Mitsugu Yamato (151-156).
Phenolic antioxidants are well known for trapping peroxy radicals to prevent organic materials from oxidative degradation. It is also important, however, to trap alkyl radicals for prevention of such degradation, because autoxidation includes both peroxy and alkyl radicals as chain carriers. In this study, on the basis of new ortho-substituent effect, o-allylphenols were molecularly designed to enhance the number of peroxy radicals trapped. It has been found by chance that some o-allylphenols can trap both peroxy and alkyl radicals, depending on the oxygen concentration of the surrounding atmosphere. The alkyl radical trapping mechanism is discussed.
Keywords: Phenol; 2-Allylphenol; Antioxidant; Alkyl radical; Peroxy radical;

The thermal decomposition behaviour of poly(propylene carbonate)s (PPC)s synthesized with varying molecular weights was studied at various pyrolysis temperatures by the combination of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analysis/infrared spectrometry (TG/IR) techniques. The pyrolysis products of PPCs with lower molecular weight of 26,900 and higher molecular weight of 144,600 at different pyrolysis temperatures were identified using Py-GC/MS. The dynamic decomposition was also explored with the TG/IR technique. The results showed that chain scission occurs at relatively lower temperature than for the unzipping reaction, and an increase in molecular weight can reduce the amount of the active terminal groups and restrict unzipping reaction to some extent. It was also observed that the backbone structure plays a great role in thermal decomposition behaviour of PPC. The same perfectly alternating structure leads to the same decomposition mechanism whereas unzipping needs a high activation energy and takes place at high decomposition temperature. The final pyrolysates are cyclic propylene carbonate, and 1,2 propanediol. Low molecular weight PPC undergoes a one-stage pyrolysis and high molecular weight PPC pyrolysis obeys two-step pyrolysis mechanism, viz. main chain random scission and unzipping. The thermal decomposition behaviour of PPC in the absence and presence of a metal complex catalyst was studied by TG/IR. It was further observed that the metal complex catalyst has little effect on the thermal decomposition of the PPC. The catalyst only slightly reduced the activation energy leading to the accelerated depolymerization reaction.
Keywords: Thermal decomposition; Polycarbonate; Carbon dioxide; Pyrolysis;

Degradation of poly(d-lactic acid) by a thermophile by Kosuke Tomita; Hideto Tsuji; Tomohiro Nakajima; Yumi Kikuchi; Kensaku Ikarashi; Noritoshi Ikeda (167-171).
A thermophile, which was isolated from soil as a microbe degrading poly(butylene succinate-co-butylene adipate) and identified as Bacillus stearothermophilus, was applied to degradation of poly(d-lactic acid) (PDLA) film. In the cultivation at 60 °C, the strain grew on PDLA and the dissolved total organic carbon (TOC) concentration in the medium changed according to the growth stage, i.e., after the TOC rapidly reached the minimum, it increased gradually. As for residual PDLA, gel permeation chromatograms showed a marked shift of the whole peak to low molecular weight region, and moreover, degree of crystallinity increased, while melting temperature decreased. PDLA was proved to be highly degraded by this strain.
Keywords: Poly(d-lactic acid); Biodegradation; Thermophile; Bacillus stearothermophilus;

Effect of novolac phenol and oligomeric aryl phosphate mixtures on flame retardance enhancement of ABS by Kunwoo Lee; Kangro Yoon; Jinhwan Kim; Jinyoung Bae; Jaeho Yang; Sanghyun Hong (173-179).
Tetra-2,6-dimethyl phenyl resorcinol diphosphate (DMP-RDP), which is one of the phosphorus flame retardants exhibiting higher evaporation temperature, and novolac phenol resin (NP) were employed to investigate whether the synergistic effect of using them together could be observed on the flame retardance of ABS. For this purpose, various NPs were incorporated into DMP-RDP as co-flame retardants and a series of ABS/DMP-RDP/NP compounds were manufactured and their flame retardancies were evaluated by measuring the limiting oxygen index (LOI) values and UL-94V classes. The results showed that the incorporation of DMP-RDP/NP mixture is very effective in enhancing the thermal stability of ABS and that the LOI value as high as 53 is obtained for a certain formulation. The reason for this finding was believed to be originated from the crosslinking reaction between –OH of NP and –OH generated from the combustion of DMP-RDP. Some direct evidences from FTIR experiments were presented. Moreover, optical microscopy analysis showed the formation of intumescent chars that were very dense. The effect of molecular weight of NP on the flame retardancies of the compounds is also discussed.
Keywords: ABS; Tetra-2,6-dimethyl phenyl resorcinol diphosphate; Novolac phenol; Flame retardance; Intumescence;

Calendar of events (183-185).