Non-isothermal crystallization, melting behavior and polymorphism of polypropylene in β-nucleated polypropylene/recycled poly(ethylene terephthalate) blends

β-Nucleated polypropylene (PP), non-compatibilized and compatibilized β-nucleated PP/recycled poly(ethylene terephthalate) (r-PET) blends were prepared on a twin-screw extruder. The compatibilizers were maleic anhydride grafted PP (PP-g-MA), glycidyl methacrylate grafted PP (PP-g-GMA), maleic anhydride grafted polyethylene-octene (POE-g-MA) and polyethylene-vinyl acetate (EVA-g-MA) elastomers. Effects of r-PET content, compatibilizer type and content, pre-melting temperature and time on the non-isothermal crystallization and melting behavior, and polymorphism of PP in the blends were investigated by differential scanning calorimeter (DSC). DSC results show that the crystallization temperature of PP crystallized predominantly in β-modification was higher than that of neat PP. In the non-compatibilized blend, PP matrix crystallized mainly in α-modification even if r-PET content was only 10 wt%. However, PP-g-MA compatibilization made PP matrix crystallize mainly in β-modification, but PP-g-GMA, POE-g-MA and EVA-g-MA did not improve the β-modification content distinctly. The α-crystal melting peak temperature of PP decreased with increasing pre-melting temperature, but r-PET content, compatibilizer type and content as well as pre-melting time had no obvious effect on the melting temperature of PP. The increase in PP-g-MA content, pre-melting temperature and time was benefit for the formation of β-modification. It is suggested that the β-nucleating agent is encapsulated or dissolved in polar r-PET in β-nucleated PP/r-PET blend, addition of PP-g-MA to the non-compatibilized blend resulted in transferring β-nucleating agent from r-PET phase into PP phase, the increase in PP-g-MA content, melting temperature and time was benefit for transferring β-nucleating agent from r-PET phase into PP phase. The non-isothermal crystallization kinetics of PP in the blends were evaluated by Mo’s method.     

Selective fluorination of m-tyrosine by OF2

Fluorine-18 labeled aromatic amino acids are routinely used as tracers in positron emission tomography (PET) to study in vivo metabolic processes. The most versatile method for the production of such radiotracers is electrophilic fluorination of the aromatic amino acid with [¹⁸F]F₂, which is most commonly produced by the gas-phase nuclear reaction ¹⁸O(p, n)¹⁸F. Although [¹⁸F]F₂ is the major product, considerable amounts of [¹⁸F]OF₂ (up to 20%) are also produced. Electrophilic fluorination reactions of l-phenylalanine, 3-nitro-l-tyrosine, 4-nitro-dl-phenylalanine, 3,4-dihydroxyphenyl-l-alanine (l-DOPA), 3-O-methyl-l-DOPA, 3,4-dimethoxy-l-phenylalanine, p-tyrosine and o-tyrosine in H₂O and of m-tyrosine in anhydrous HF (aHF), CF₃SO₃H, CF₃COOH, CH₃COOH, HCOOH and H₂O using OF₂ were investigated. Although F₂ is an efficient fluorinating agent in aHF, electrophilic fluorination reactions using OF₂ were shown to be most efficient in less acidic media such as H₂O. In addition, and contrary to reports that OF₂ and F₂ have similar reactivities, m-tyrosine was the only aromatic system studied that was fluorinated by OF₂ and this was optimum in H₂O for the fluorinated m-tyrosine isomers (total yield, 4.35 ± 0.04%). The presence of [¹⁸F]OF₂ byproduct has no significant impact on the fluorination of aromatic amino acids investigated in this study and the subsequent production of their corresponding ¹⁸F-labeled radiotracers for patient use.     

Pyrene based Schiff base ligand: A highly selective fluorescence chemosensor for the detection of Cu2+ ions

A Schiff base ligand L has been designed and synthesized by the condensation of 1′-Hydroxy-2′-acetonaphthonehydrazide with pyrene aldehyde for the detection of Cu²⁺ ions. The ligand was spectroscopically characterized by all possible techniques. Among different metal ions, Cu²⁺ ions give a tremendous enhancement of fluorescence intensity in 20% water with THF. The “Turn-On” fluorescence for Cu²⁺ ions utilizes the Photo-induced Electron Transfer (PET) mechanism. It has been observed that the presence of relevant cations and anions did not affect the probe's fluorescence intensity. The stoichiometric binding mode of the complex is confirmed using Job's method. The low detection limit and reversibility make it cost-effective.     

Dual Photo-Responsive Diphenylacetylene Enables PET In-Situ Upcycling with Reverse Enhanced UV-Resistance and Strength

A novel in situ chemical upcycling strategy for plastic waste is proposed by the customized diphenylacetylene monomer with dual photo-response. That is, diphenylacetylene reactive monomers are in situ inserted into the macromolecular chain of polyethylene terephthalate (PET) plastics/fibers through one-pot transesterification of slight-depolymerization and re-polymerization. On the one hand, the diphenylacetylene group absorbs short-wave high-energy UV rays and then releases long-wave low-energy harmless fluorescence. On the other hand, the UV-induced photo-crosslinking reaction among diphenylacetylene groups produces extended π-conjugated structure, resulting in a red-shift (due to decreased HOMO–LUMO separation) in the UV absorption band and locked crosslink points between PET chains. Therefore, with increasing UV exposure time, the upcycled PET plastics exhibit reverse enhanced UV resistance and mechanical strength (superior to original performance), instead of serious UV-photodegradation and damaged performance. This upcycling strategy at oligomer-scale not only provides a new idea for traditional plastic recycling, but also solves the common problem of gradual degradation of polymer performance during use.     

剪刀型双卟啉锌配合物在Cu+离子和DABCO双客体调控下的荧光开关效应

设计了一个含有双包合功能的剪刀型双卟啉锌化合物1(1,8-二{4-[N-(N,N-锌-5,10,15,20-四苯基卟啉-4'-取代)-氨基羰基]苄氧基}蒽醌). 通过荧光、紫外-可见光谱和核磁共振谱滴定实验证实, 化合物1能分别与金属离子和含氮双齿客体作用, Cu+离子和游离DABCO(1,4-偶氮双环[2,2,2]辛烷)都能导致化合物1中卟啉发光团的荧光猝灭, 它们的荧光猝灭机制分别源于光诱导电子转移过程(PET)和配体交换引起的电荷转移过程. Cu+离子和游离DABCO两种客体在氯仿溶液中可以相互作为彼此的捕获剂, 通过循环地加入这两种客体, 可以构筑一个双客体调控的OFF/ON荧光开关.     

STUDY ON THE EFFECTS OF TLCP ON PYROLYSIS OF PET AND ITS RETARDANT MECHANISM

The flame retardancy of aromatic thermotropic liquid crystal phosphorus-containing copolyester,TLCP,on PET was investigated.The results show that the presence of TLCP promotes char formation of the substrate and enhances thermal stability of char,hence delay its decomposition.SEM pictures show that the char formed from PET/TLCP is more compact, therefore is more resistant to fire and heat than that from pure PET.Evolved gas analysis by I.R measurements indicates that TLCP would decompose to produce phosp...     

The role of crystalline, mobile amorphous and rigid amorphous fractions in the performance of recycled poly (ethylene terephthalate) (PET)

The action of thermo-mechanical degradation induced by mechanical recycling of poly(ethylene terephthalate) was simulated by successive injection moulding cycles. Degradation reactions provoked chain scissions and a reduction in molar mass mainly driven by the reduction of diethyleneglycol to ethylene glycol units in the flexible domain of the PET backbone, and the formation of -OH terminated species with shorter chain length. The consequent microstructural changes were quantified taking into account a three-fraction model involving crystalline, mobile amorphous (MAF) and rigid amorphous fractions (RAF). A remarkable increase of RAF, to a detriment of MAF was observed, while the percentage of crystalline fraction remained nearly constant. A deeper analysis of the melting behaviour, the segmental dynamics around the glass-rubber relaxation, and the macroscopic mechanical performance, showed the role of each fraction leading to a loss of thermal, viscoelastic and mechanical features, particularly remarkable after the first processing cycle.     

Triphenylamine-based novel PET sensors in selective recognition of dicarboxylic acids

The triphenylamine-based chemosensors 1 and 2 have been designed and synthesized, for the first time, for the selective recognition of dicarboxylic acids. Carboxylic acid binding takes place through charge neutral pyridyl amide receptor sites with concomitant quenching of fluorescence of the triphenylamine moiety. The bindings were examined using ¹H NMR, fluorescence and UV-vis spectroscopic methods. The receptor 1 was found to be selective for glutaric and adipic acids and the macrocycle 2 was specific for 2,2-dimethylmalonic acid.     

Improved syntheses of precursors for PET radioligands [F]XTRA and [F]AZAN

Improved syntheses of 7-methyl-2-exo-[3′-(2-bromopyridin-3-yl)-5′-pyridinyl]-7-azabicyclo[2.2.1]heptanes (3) and 7-methyl-2-exo-[3’-(6-bromopyridin-2-yl)-5′-pyridinyl]-7-azabicyclo[2.2.1]heptanes (4), precursors for PET radioligands [¹⁸F]XTRA (1) and [¹⁸F]AZAN (2), involving a key Stille coupling step followed by deprotection of Boc group and N-methylation are described. The new synthetic procedures provided the title compounds in more than 40% overall yields.     

Mechanism of stress cracking of poly(ethylene terephthalate) beverage bottles: A method for the prevention of stress cracking based on water hardness

A recently described bottle test method was used to evaluate the dependence of stress crack failure of poly(ethylene terephthalate) (PET) carbonated soft drink bottles on water hardness. Although the industry belief is that water hardness is irrelevant to stress cracking, it was found that hardness ions exert a tremendous positive impact by deactivating water alkalinity through precipitation as harmless carbonate minerals. This mitigating effect of hardness means that no complete understanding of stress cracking as a function of alkalinity is possible without also considering water hardness. A useful concept is that of excess alkalinity, which is defined as alkalinity that is not precipitated during solution evaporation. Limiting excess alkalinity by using water with sufficient hardness is an effective means of stress crack prevention in PET soft drink bottles. Evaluation of compositions which are typical of those used for lubricating PET bottles on production conveyors showed that the role of these compositions in stress cracking was that of spectators, that is, they neither cause failure if water does not otherwise cause it, nor stop failure if water otherwise causes it.