scholarly journals The structure and glass transition behavior of PLLA under the influence of gamma radiation

2010 ◽  
Vol 64 (4) ◽  
pp. 275-281
Author(s):  
Dejan Milicevic ◽  
Sasa Trifunovic ◽  
Tihana Mudrinic ◽  
Andreja Leskovac ◽  
Nenad Ignjatovic ◽  
...  
Keyword(s):  
Activation Energy ◽  
Molecular Weight ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Gamma Radiation ◽  
Apparent Activation Energy ◽  
Absorbed Dose ◽  
Chain Scission ◽  
Transition Behaviour

The influence of gamma radiation on the structure and glass transition behavior of poly-L-lactide (PLLA) has been studied. Since PLLA exposed to high-energy radiation in the presence of air is prone to chain scission reactions and large degradation, changes in molecular weight were obtained by the gel permeation chromatography (GPC). Alterations in the glass transition behaviour were investigated by differential scanning calorimetry (DSC). The apparent activation energy, ?H*, for the glass transition was determined on the basis of the heating rate dependence of the glass transition temperature, Tg. Our findings support the fact that chain scission is the main reason for the decrease of Tg and ?H* with the absorbed dose. At low doses, despite large changes in molecular weight, only small alterations are observed in the glass transition temperature and apparent activation energy. Further increase in the absorbed dose introduces not only significant changes in the molecular weight but also in the glass transition temperature and the activation energy. Such glass transition behaviour is a manifestation of a well-known effect of molecular weight on Tg, postulated by the Fox-Flory equation. However, all the observed alterations are small and tolerable at absorbed doses required for sterilization (up to 25 kGy in most circumstances). Furthermore, this study reveals that the radiation-induced changes in the molecular weight and the glass transition temperature occur in a predictable and fairly accurate manner. Therefore, gamma radiation can be used not only for sterilization but also for tailoring desirable end-use properties of PLLA based implants.

The Influence of Gamma Radiation on the Glass Transition of Hydroxyapatite/Poly L-Lactide Composite

2007 ◽  
Vol 555 ◽  
pp. 497-502
Author(s):  
Dejan Miličević ◽  
S. Trifunović ◽  
N. Ignjatović ◽  
E. Suljovrujić
Keyword(s):  
Activation Energy ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Structural Relaxation ◽  
Absorbed Dose ◽  
Gel Permeation Chromatography ◽  
Chain Scission ◽  
Scanning Calorimetry ◽  
Dsc Measurements

Hydroxyapatite/poly L-lactide (HAp/PLLA) is a composite biomaterial which has been widely utilized for substitution and reparation of the hard bone tissue. It is well known that gamma irradiation has been successfully employed in the modification/sterilization of such porous composites and that it has advantages over other procedures. In this study, differential scanning calorimetry (DSC) measurements were made to investigate the influence of the radiation on glass transition behavior and structural relaxation, as well as to estimate the activation energy for this process. The apparent activation energy ΔH* for structural relaxation in the glass transition region was determined on the basis of the heating rate dependence of the glass transition temperature Tg. Furthermore, the results were correlated with those obtained by gel permeation chromatography (GPC). Our findings support the fact that the radiation-induced chain scission in the PLLA phase is the main reason for the decrease of the glass transition temperature and/or activation energy with the absorbed dose.

The damping properties of dealloyed porous copper and its PMMA composite

1994 ◽  
Vol 9 (11) ◽  
pp. 2884-2890
Author(s):  
Un-Sig Min ◽  
James C.M. Li
Keyword(s):  
Activation Energy ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Apparent Activation Energy ◽  
Volume Fraction ◽  
Pure Copper ◽  
Damping Properties ◽  
Young’S Moduli ◽  
Porous Copper

Incramute Cu-Mn alloys were dealloyed to remove Mn by selective electrolytic separation. The porous dealloyed specimens were compressed at 0.17-14 GPa, resulting in densities of 55-88% of the density of pure copper. Some porous copper specimens before compression were soaked in a mixture of monomer (MMA) and the initiator (AIBN), compressed, and then polymerized by heating. Young's moduli of both the dealloyed porous copper and its PMMA composite were found to decrease exponentially with porosity and volume fraction of PMMA, respectively. The apparent activation energy for damping of Cu-PMMA composite near the glass transition temperature of PMMA was found to increase with decreasing volume fraction of PMMA.

Imide Oligomers Containing Pendent and Terminal Phenylethynyl Groups—II

1998 ◽  
Vol 10 (3) ◽  
pp. 273-283 ◽  
Author(s):  
J W Connell ◽  
J G Smith ◽  
P M Hergenrother
Keyword(s):  
Molecular Weight ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Average Molecular Weight ◽  
Adhesive Tape ◽  
High Glass Transition Temperature ◽  
Compressive Properties ◽  
Compression Moulding ◽  
Imide Oligomers

As part of a programme to develop high-performance/high-temperature structural resins for aeronautical applications, imide oligomers containing pendent and terminal phenylethynyl groups were prepared, characterized and the cured resins evaluated as composite matrices. The oligomers were prepared at a calculated number-average molecular weight of 5000 g mol−1 and contained 15–20 mol% pendent phenylethynyl groups. In previous work, an oligomer containing pendent and terminal phenylethynyl groups exhibited a high glass transition temperature (∼313 °C), and laminates therefrom exhibited high compressive properties, but processability, fracture toughness, microcrack resistance and damage tolerance were less than desired. In an attempt to improve these deficiencies, modifications in the oligomeric backbone involving the incorporation of 1,3-bis(3-aminophenoxy)benzene were investigated as a means of improving processability and toughness without detracting from the high glass transition temperature and high compressive properties. The amide acid oligomeric solutions were prepared in N-methyl-2-pyrrolidinone and were subsequently processed into imide powder, thin films, adhesive tape and carbon fibre prepreg. Neat resin plaques were fabricated from imide powder by compression moulding. The maximum processing pressure was 1.4 MPa and the cure temperature ranged from 350 to 371 °C for 1 h for the mouldings, adhesives, films and composites. The properties of the 1,3-bis(3-aminophenoxy)benzene modified cured imide oligomers containing pendent and terminal phenylethynyl groups are compared with those of previously prepared oligomers containing pendent and terminal phenylethynyl groups of similar composition and molecular weight.

Study on the Crystallization Activation Energy of Poly (L-lactic acid) Nucleated with P-tert-butylcalix[8]arene

2018 ◽  
Vol 26 (2) ◽  
pp. 169-175
Author(s):  
Yaoqi Shi ◽  
Liang Wen ◽  
Zhong Xin
Keyword(s):  
Activation Energy ◽  
Lactic Acid ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Crystallization Temperature ◽  
Nucleating Agent ◽  
Crystallization Activation Energy ◽  
Temperature Range ◽  
Chain Mobility

The crystallization activation energy (Δ E) of a polymer comprises the nucleation activation energy Δ F and the transport activation energy Δ E*. In this paper, the Δ E of poly (L-lactic acid) (PLLA) nucleated with nucleating agent p- tert-butylcalix[8]arene (tBC8) was calculated. The results showed that the Δ E of nucleated PLLA was 165.97 kJ/mol, which is higher than that of pure PLLA. The reason why Δ E of PLLA increased when incorporating nucleating agent was studied. The increment of glass transition temperature ( Tg) for nucleated PLLA revealed that the polymer chain mobility was restricted by tBC8, which was considered as the reason for the increase of Δ E*. Further, polyethylene glycol (PEG) was added to improve the chain mobility, thus eliminated the variation of the transport activation energy Δ E* caused by tBC8. Then the effect of the increment of crystallization temperature range on the increase of Δ F was also taken into consideration. It was concluded that both decreasing the mobility of chain segments and increasing the crystallization temperature range caused an increase of Δ E for PLLA/tBC8.

Properties of Hyperbranched Polyglycidol’s Derivatives

2020 ◽  
Vol 869 ◽  
pp. 190-195
Author(s):  
Yuri Mikhailov ◽  
Ludmila Romanova ◽  
Anna Darovskikh ◽  
Nilson Garifullin
Keyword(s):  
Molecular Weight ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Functional Groups ◽  
Enthalpy Of Formation ◽  
Rheological Parameters ◽  
Weight Composition ◽  
Composition And Structure

Some properties (enthalpy of formation, glass transition temperature and rheological parameters) of hyperbranched polyglycidol derivatives containing nitrate and azide functional groups were investigated. The dependence of the found properties on the molecular weight, composition and structure of the investigated substances was determined.

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