Thermal degradation kinetics of the biodegradable aliphatic polyester, poly(propylene succinate)

The preparation of the biodegradable aliphatic polyester poly(propylene succinate) (PPSu) using 1,3-propanediol and succinic acid is presented. Its synthesis was performed by two-stage melt polycondensation in a glass batch reactor. The polyester was characterized by gel permeation chromatography, ¹H NMR spectroscopy and differential scanning calorimetry (DSC). It has a number average molecular weight 6880 g/mol, peak temperature of melting at 44 °C for heating rate 20 °C/min and glass transition temperature at −36 °C. After melt quenching it can be made completely amorphous due to its low crystallization rate. According to thermogravimetric measurements, PPSu shows a very high thermal stability as its major decomposition rate is at 404 °C (heating rate 10 °C/min). This is very high compared with aliphatic polyesters and can be compared to the decomposition temperature of aromatic polyesters. TG and Differential TG (DTG) thermograms revealed that PPSu degradation takes place in two stages, the first being at low temperatures that corresponds to a very small mass loss of about 7%, the second at elevated temperatures being the main degradation stage. Both stages are attributed to different decomposition mechanisms as is verified from activation energy determined with isoconversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures is auto-catalysis with activation energy E = 157 kJ/mol while the second mechanism is a first-order reaction with E = 221 kJ/mol, as calculated by the fitting of experimental measurements.     

Effect of different nanoparticles on thermal decomposition of poly(propylene sebacate)/nanocomposites: Evaluation of mechanisms using TGA and TG–FTIR–GC/MS

In the present study poly(propylene sebacate) (PPSeb) nanocomposites containing 2 wt% of fumed silica nanoparticles (SiO₂) or multiwalled carbon nanotubes (MWCNTs), or montmorillonite (MMT) were prepared by in situ polymerization. The thermal degradation of nanocomposites was studied using thermogravimetric analysis (TGA). It was found that the addition of MWCNTs and MMT enhances the thermal stability of the polymer, while SiO₂ nanoparticles do not affect it. From the variation of the activation energy (E) with increasing degree of conversion it was found that the decomposition of nanocomposites proceeded with a complex reaction mechanism with the participation of at least two different steps. To evaluate the thermal decomposition mechanisms and mainly the effect of nanoparticles on the thermal decomposition of PPSeb, TGA/FTIR and a combination of TG-gas chromatography–mass spectrometry (TG/GC–MS) were used. From mass ions detection of the formed decomposition compounds it was found that the decomposition of PPSeb and its nanocomposites, takes place mainly through β-hydrogen bond scission and, secondarily, through α-hydrogen bond scission. The main decomposition products were aldehydes, alcohols, allyl, diallyl, and carboxylic acids.     

Investigation of thermal degradation mechanism of an aliphatic polyester using pyrolysis-gas chromatography-mass spectrometry and a kinetic study of the effect of the amount of polymerisation catalyst

The thermal degradation mechanism of the aliphatic biodegradable polyester poly(propylene succinate) (PPSu) and the effect of the polymerisation catalyst (tetrabutyl titanate, TBT) were studied using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and TGA analysis. It is found from mass ions detection, that the decomposition takes place, mainly, through β-hydrogen bond scission and secondarily by α-hydrogen bond scission. At low pyrolysis temperatures (360 and 385 °C) gases as well as succinic anhydride, succinic acid and propanoic acid are mainly produced while allyl and diallyl succinates are formed in smaller quantities. At high temperatures (450 °C) the behaviour is inverted. Using the isoconversional methods of Ozawa and Friedman it is founded that PPSu degrades by two consecutive mechanisms. According to this analysis the first mechanism that takes place at low temperatures is autocatalysis with an activation energy of about E = 110-120 kJ/mol. The second mechanism is a first-order reaction with E of 220 kJ/mol, and corresponds to the extended β- and α-hydrogen bond scissions. These activation energies are slightly dependent on the catalyst amount and are shifted towards lower values with an increase of TBT content from 3 × 10⁻⁴ to 3 × 10⁻¹ mol TBT/mol succinic acid (SA).     

Thermal degradation mechanism of poly(ethylene succinate) and poly(butylene succinate): Comparative study

Two aliphatic polyesters that consisted from succinic acid, ethylene glycol and butylene glycol, —poly(ethylene succinate) (PESu) and poly(butylene succinate) (PBSu)—, were prepared by melt polycondensation process in a glass batch reactor. These polyesters were characterized by DSC, ¹H NMR and molecular weight distribution. Their number average molecular weight is almost identical in both polyesters, close to 7000 g/mol, as well as their carboxyl end groups (80 eq/10⁶ g). From TG and Differential TG (DTG) thermograms it was found that the decomposition step appears at a temperature 399 °C for PBSu and 413 °C for PESu. This is an indication that PESu is more stable than PBSu and that chemical structure plays an important role in the thermal decomposition process. In both polyesters degradation takes place in two stages, the first that corresponds to a very small mass loss, and the second at elevated temperatures being the main degradation stage. The two stages are attributed to different decomposition mechanisms as is verified from the values of activation energy determined with iso-conversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures, is auto-catalysis with activation energy E = 128 and E = 182 kJ/mol and reaction order n = 0.75 and 1.84 for PBSu and PESu, respectively. The second mechanism is nth-order reaction with E = 189 and 256 kJ/mol and reaction order n = 0.68 and 0.96 for PBSu and PESu, respectively, as they were calculated from the fitting of experimental results.     

Influence of chemical structure on physicochemical properties and thermal decomposition of the fully bio-based poly(propylene succinate-co-butylene succinate)s

In this work, two polyesters and four copolyesters were studied. All materials were synthesized to obtain the monomers dedicated for thermoplastic polyurethane elastomers. For this type of PUR, the monomers should characterize by appropriate selected physicochemical properties and macromolecular structure distribution, which depends on synthesis conditions. The study of chemical structure with extensive and knowledgeable analysis of formed macromolecules of synthesized bio-based copolyesters was conducted with the use of FTIR and ¹H NMR spectroscopy and MALDI-ToF mass spectrometry. The results allowed to propose the majority of probable chemical structures of macromolecules formed during synthesis. Moreover, the impact of the structure on the thermal stability of the obtained copolyesters was also determined with the use of thermogravimetric analysis. The temperature of the beginning of thermal decomposition equaled even 330 °C. Furthermore, the results of DSC-TG/QMS coupled method confirmed that all prepared polyesters degraded by α and β-hydrogen bond scission mechanisms.     

Novel random poly(propylene isophthalate/adipate) copolyesters: Synthesis and characterization

Poly(propylene adipate) (PPA) and poly(propylene isophthalate/adipate) (PPI-PPA) random copolymers of various compositions were synthesized in bulk and characterized in terms of chemical structure and molecular weight. Furthermore, the thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All the polymers showed a good thermal stability. At room temperature they appeared as semicrystalline materials, except the copolymers containing 20 and 30 mol% of PI units: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to homopolymers. The crystalline phase of PPI and PPA was evidenced at high content of propylene isophthalate or propylene adipate units, respectively. Amorphous samples were obtained after melt quenching and an increment of T_g as the content of PI units is increased was observed. This behavior was explained as due to the stiff phenylene groups in the polymeric chain. The Wood equation was found to describe well T_g-composition data. Lastly, the presence of a rigid-amorphous phase was evidenced in the copolymers, differently from PPA homopolymer.     

Neopenthyl glycol containing poly(propylene azelate)s: Synthesis and thermal properties

Poly(neopenthyl azelate) (PNAz) and poly(propylene/neopenthyl azelate) random copolymers (PPAz-PNAz) (NAz unit content from 5 to 20 mol%) were synthesized and characterized in terms of chemical structure and molecular weight. Afterwards, the polyesters were examined by TGA, DSC and X-ray diffractometry. Good thermal stability was found for each sample. The thermal analysis showed that the T_m of the copolymers decreased with the increment in NAz unit content, differently from T_g, which on the contrary increased. X-ray diffraction measurements allowed the identification of the PPAz crystalline structure in all the copolymers. Multiple endotherms were shown in the PPAz-PNAz samples, due to melting and recrystallization processes, similarly to PPAz. The of the copolymers was derived from the application of the Hoffman-Weeks’ method. Baur’s equation described well the T_m-composition data. The isothermal crystallization kinetics were analyzed according to Avrami’s treatment. The introduction of NAz units decreased the crystallization rate compared to pure PPAz. Values of the Avrami’s exponent n close to 3 were obtained in all cases, regardless of T_c, in agreement with a crystallization process originating from predeterminated nuclei and characterized by a three dimensional spherulitic growth.     

Decomposition of poly(propylene carbonate) with UV sensitive iodonium salts

The decomposition characteristics of poly(propylene carbonate) containing a photoacid generator have been studied. The influence of casting solvent, photoacid concentration and type, UV exposure dose, substrate surface, and ambient gas were included in this study. Dynamic thermogravimetric analysis was used to analyze the decomposition characteristics. Kinetic parameters were extracted using the Kissinger method and the Coats-Redfern method. Fourier Transform Infrared Spectroscopy was used to analyze effects of casting solvent. The highest thermal stability was found to occur in high molecular weight, high-purity poly(propylene carbonate) samples. Cyclohexanone and trichloroethylene solvents were found to increase the thermal stability. Photoacid generators based on diphenyliodonium salts lowered the onset decomposition temperature and activation energy.     

Miscibility and enzymatic degradation studies of poly(ε-caprolactone)/poly(propylene succinate) blends

In the present study the miscibility behaviour and the biodegradability of poly(ε-caprolactone)/poly(propylene succinate) (PCL/PPSu) blends were investigated. Both of these aliphatic polyesters were laboratory synthesized. For the polymer characterization DSC, ¹H NMR, WAXD and molecular weight measurements were performed. Blends of the polymers with compositions 90/10, 80/20, 70/30 and 60/40 w/w were prepared by solution-casting. DSC analysis of the prepared blends indicated only a very limited miscibility in the melt phase since the polymer-polymer interaction parameter χ₁₂ was −0.11. In the case of crystallized specimens two distinct phases existed in all studied compositions as it was found by SEM micrographs and the particle size distribution of PPSu dispersed phase increased with increasing PPSu content. Enzymatic hydrolysis for several days of the prepared blends was performed using Rhizopus delemar lipase at pH 7.2 and 30 °C. SEM micrographs of thin film surfaces revealed that hydrolysis affected mainly the PPSu polymer as well as the amorphous phase of PCL. For all polymer blends an increase of the melting temperatures and the heat of fusions was recorded after the hydrolysis. The biodegradation rates as expressed in terms of weight loss were faster for the blends with higher PPSu content. Finally, a simple theoretical kinetic model was developed to describe the enzymatic hydrolysis of the blends and the Michaelis-Menten parameters were estimated.     

Miscibility of biodegradable poly(propylene succinate)/poly(propylene adipate) blends: Effect of the transesterification reactions

The miscibility of poly(propylene succinate)/poly(propylene adipate) blends was investigated by means of DSC, WAXS and NMR techniques. Poly(propylene succinate) and poly(propylene adipate) were found to be completely immiscible in as blended-state. The miscibility changes upon extended mixing at elevated temperature: for enough long mixing time, the original two phases gradually merged into a single one because of transesterification reactions. The NMR analysis showed that the transesterifications led to block copolymers whose average sequence length decreased as the mixing time is increased at a fixed temperature. Upon very long mixing time (150 min), all PPS and PPA chains are fully transformed into a random copolymer characterized by a single amorphous phase.     

Effect of poly(vinyl acetate) (PVAc) on thermal behavior and mechanical properties of poly(3-hydroxybutyrate)/poly(propylene carbonate) (PHB/PPC) blends

To assess the compatibility of blends of synthetic poly(propylene carbonate) (PPC), with a natural bacterial poly(3-hydroxybutyrate) (PHB), a simple casting procedure of blend was used. poly(3-hydroxybutyrate)/poly(propylene carbonate) blends are found to be incompatible according to DSC and DMA analysis. In order to improve the compatibility and mechanical properties of PHB/PPC blends, poly(vinyl acetate) (PVAc) was added as a compatibilizer. The effects of PVAc on the thermal behavior, morphology, and mechanical properties of 70PHB/30PPC blend were investigated. The results show that the melting point and the crystallization temperature of PHB in blends decrease with the increase of PVAc content in blends, the loss factor changes from two separate peaks of 70PHB/30PPC blend to one peak of 70PHB/30PPC/12PVAc blend. It is also found that adding PVAc into 70PHB/30PPC blend can decrease the size of dispersed phase from morphology analysis. The result of tensile properties shows that PVAc can increase the tensile strength and Young’s modulus of 70PHB/30PPC blend, and both the elongation at break and the tensile toughness increase significantly with PVAc added into 70PHB/30PPC.     

不同催化剂作用下聚乳酸/聚碳酸亚丙酯的酯交换反应

选用辛酸亚锡[Sn(Oct)₂]和钛酸四丁酯(TBT)作为聚乳酸(PLA)/聚碳酸亚丙酯(PPC)的酯交换反应催化剂, 研究了溶液条件下单一催化剂及复合催化剂对PLA/PPC酯交换反应的催化作用. 通过对反应产物的分子结构、 热力学及流变学行为进行分析, 结果发现, 无论在单一催化剂还是复合催化剂作用下, PLA与PPC分子间均发生了酯交换反应, 同时伴随着断链反应. 其中, 当Sn(Oct)₂作为单一催化剂或Sn(Oct)₂/TBT作为复合催化剂时, 样品更倾向发生断链反应而非显著的酯交换反应. 进一步分析纯样品在催化剂Sn(Oct)₂或TBT作用下的反应情况, 结果发现, PPC在反应最初阶段以高分子量的分子链断链为主, 且会发生明显的解拉链降解, 从而导致PLA/PPC在等质量比时酯交换反应程度不高, 这为今后更好地研究PLA/PPC酯交换反应提供了思路.     

Synthesis, characterization and thermal degradation mechanism of three poly(alkylene adipate)s: Comparative study

Three high molecular weight aliphatic polyesters derived from adipic acid and the appropriate diol - poly(ethylene adipate) (PEAd), poly(propylene adipate) (PPAd) and poly(butylene adipate) (PBAd) - were prepared by two-stage melt polycondensation method (esterification and polycondensation) in a glass batch reactor. Intrinsic viscosities, GPC, DSC, NMR and carboxylic end-group measurements were used for their characterization. Mechanical properties of the prepared polyesters showed that PPAd has similar tensile strength to low-density polyethylene while PEAd and PBAd are much higher. From TGA analysis it was found that PEAd and PPAd have lower thermal stability than poly(butylene adipate) (PBAd). The decomposition kinetic parameters of all polyesters were calculated while the activation energies were estimated using the Ozawa, Flynn and Wall (OFW) and Friedman methods. Thermal degradation of PEAd was found to be satisfactorily described by one mechanism, with activation energy 153 kJ/mol, while that of PPAd and PBAd by two mechanisms having different activation energies: the first corresponding to a small mass loss with activation energies 121 and 185 kJ/mol for PPAd and PBAd, respectively, while the second is attributed to the main decomposition mechanism, where substantial mass loss takes place, with activation energies 157 and 217 kJ/mol, respectively.     

Thermal and weathering degradation of poly(propylene carbonate)

High molecular-weight poly(propylene carbonate) (PPC) can remain intact upon storage in ambient air or in water for 8 months once the catalyst is completely removed. Catalyst-free pure PPC is also thermally stable below 180 °C. At 200 °C, degradation occurs, mainly due to attack of the chain-ended hydroxyl group onto a carbonate linkage, through which the molecular weight distribution is broadened by simultaneous formation of low and high molecular weight fractions. Incomplete removal of hydrogen peroxide generated during the catalyst preparation results in a prepared polymer that contains a substantial amount of polymer chains grown biaxially from hydrogen peroxide, which gives rise to more severe thermal degradation. Experiments conducted in a weathering chamber at high temperature (63 °C) and high humidity (50%) revealed another degradation process involving chain scission through an attack of water molecules onto the carbonate linkage, which progressively and temporally lowers molecular weight.     

Thermal and dynamic mechanical properties of poly(propylene carbonate)

Summary Thermal and dynamic mechanical properties of carbon dioxide and propylene oxide alternative copolymer, poly(propylene carbonate) (PPC), and the end-capped PPC with maleic anhydride were investigated by means of TG and DMA. A master curve of the storage modulus vs. frequency can be deduced from the isochronal curves. Physical parameters of both plain and MA end-capped PPC were discussed. The results showed that for maleic anhydride (MA) end-capping PPC, an improvement of its thermal stability and mechanical properties accompanied with some modifications of the viscoelastic behavior were obtained.     

Thermal,mechanical and rheological properties of biodegradable poly(propylene carbonate) and poly(butylene carbonate) blends

Poly(propylene carbonate)(PPC) was melt blended in a batch mixer with poly(butylene carbonate)(PBC) in an effort to improve the toughness of the PPC without compromising its biodegradability and biocompatibility. DMA results showed that the PPC/PBC blends were an immiscible two-phase system. With the increase in PBC content, the PPC/PBC blends showed decreased tensile strength, however, the elongation at break was increased to 230% for the 50/50 PPC/PBC blend. From the tensile strength experiments, the Pukanszky model gave credit to the modest interfacial adhesion between PPC and PBC, although PPC/PBC was immscible. The impact strength increased significantly which indicated the toughening effects of the PBC on PPC. SEM examination showed that cavitation and shear yielding were the major toughening mechanisms in the blends subjected the impact tests. TGA measurements showed that the thermal stability of PPC decreased with the incorporation of PBC. Rheological investigation demonstrated that the addition of PBC reduced the value of storage modulus, loss modulus and complex viscosity of the PPC/PBC blends to some extent. Moreover, the addition of PBC was found to increase the processability of PPC in extrusion. The introduction of PBC provided an efficient and novel toughened method to extend the application area of PPC.     

Synthesis,thermal characterization,and tensile properties of alipharomatic polyesters derived from 1,3‐propanediol and terephthalic,isophthalic, and 2,6‐naphthalenedicarboxylic acid

In this work, three alipharomatic polyesters—poly(propylene terephthalate) (PPT), poly(propylene isophthalate) (PPI), and poly(propylene naphthalate) (PPN)—were prepared and studied with the aliphatic diol 1,3‐propanediol and the corresponding aromatic diacids. Their synthesis was performed by the two‐stage melt polycondensation method in a glass batch reactor. The thermal characterization of these polyesters was carried out with different thermal techniques such as simultaneous thermogravimetry/differential thermal analysis, thermomechanical analysis (TMA), and dynamic thermomechanical analysis. From the recorded values for the glass‐transition temperature (T_g) and melting temperature with all the aforementioned techniques, it could be said that they were in good agreement. According to the thermogravimetric results, PPT and PPI showed about the same thermal stability, whereas PPN seemed to be somewhere more thermostable. Remarkably, a transition existed immediately after T_g that was realized by the first derivative of TMA, and it was characterized as a midrange transition. For all polyesters, the average coefficient of linear thermal expansion was calculated with TMA. The secondary relaxations T_β and T_γ, recorded with dynamic mechanical thermal analysis, were mainly affected by the kinds of monomers. Concerning the mechanical properties, PPN had the highest tensile strength at break, whereas PPT had the highest elongation at break. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3998–4011, 2005     

Effect of molecular weight on thermal degradation mechanism of the biodegradable polyester poly(ethylene succinate)

A series of aliphatic polyesters, in particular poly(ethylene succinate), having different molecular weights, were synthesized from succinic acid and ethylene glycol, following the melt polycondensation process. Intrinsic viscosities (IV), GPC, DSC, ¹H NMR and carboxylic end group measurements were used for their characterisation. From thermogravimetric analysis, it was concluded that the molecular weight of polyesters achieved during polycondensation are strongly related to thermal stabilities of initial oligomers. In order to synthesise high molecular weight polyesters, the number average molecular weight of oligomers must not be lower than 2300–3000 g/mol, since thermal decomposition begins at temperatures lower than 200 °C. However, even in that case, polycondensation temperatures must not exceed 230–240 °C. From TGA studies, it was found that sample having different molecular weights could be divided into two groups characterized by different thermal stability. In the first group, belong samples with intrinsic viscosity of IV = 0.08 dL/g and in the second one all the other samples (IV > 15 dL/g). From kinetic analysis of thermal degradation, it was found that degradation of all polyesters takes place in three stages, its one corresponding to a different mechanisms. Degradation of samples with low molecular weight is more complex that that of polyesters having high molecular weights. The values of the activation energy and the exponent n for the two groups of samples—with different molecular weight—are similar, regarding the first two mechanisms, while there is an alteration in the case of the third mechanism.     

Thermal stability and flame retardant effects of halloysite nanotubes on poly(propylene)

Naturally occurred halloysite nanotubes (HNTs) with hollow nanotubular structures were used as a new type filler for poly(propylene) (PP). Nanocomposites based on PP and HNTs were prepared by melt blending. Scanning electronic microscopy (SEM) results suggested HNTs were dispersed in PP matrix evenly at nanoscale after facile modification. Thermal stability of the nanocomposites was found remarkably enhanced by the incorporation of HNTs. Cone calorimetric data also showed the decrease of flammability of the nanocomposites. Entrapment mechanism of the decomposition products in HNTs was proposed to explain the enhancement of thermal stability of the nanocomposites. The barriers for heat and mass transport, the presence of iron in HNTs, are all responsible for the improvement in thermal stability and decrease in flammability. Those results suggested potential promising flame retardant application of HNTs in PP.     

Thermal degradation behaviour of aromatic poly(ester-amide) with pendant phosphorus groups investigated by pyrolysis-GC/MS

The thermal stability of a novel phosphorus-containing aromatic poly(ester-amide) ODOP-PEA was investigated by thermogravimetric analysis (TGA). The weight of ODOP-PEA fell slightly at the temperature range of 300-400 °C in the TGA analysis, and the major weight loss occurred at 500 °C. The structural identification of the volatile products resulted from the ODOP-PEA pyrolysis at different temperatures was performed by pyrolysis-gas chromatography/mass spectrometry (pyrolysis-GC/MS). The P-C bond linked between the pendant DOPO group and the polymer chain disconnected first at approximately 275 °C, indicating that it is the weakest bond in the ODOP-PEA. The P-O bond in the pendant DOPO group was stable up to 300 °C. The cleavage of the ester linkage within the polymer main chain initiated at 400 °C, and the amide bond scission occurred at greater than 400 °C. The structures of the decomposition products were used to propose the degradation processes happening during the pyrolysis of the polymer.