Thermal Crystallization of Polytetrahydrofuran Networks

1991 ◽  
Vol 64 (1) ◽  
pp. 74-82 ◽  
Author(s):  
C. Michael Roland ◽  
Gary S. Buckley
Keyword(s):  
Melting Point ◽  
Crystallization Behavior ◽  
Degree Of Crystallinity ◽  
Melting Point Depression ◽  
Network Architectures ◽  
Experimental Conditions ◽  
Thermal Crystallization ◽  
Melting Temperatures ◽  
Equilibrium Melting Point ◽  
The Degree Of Crystallinity

Abstract The formation of a network in PTHF inhibits the crystallization of chain units in proximity to the crosslinks. From melting-point-depression measurements, it is estimated that the suppression in crystallizability extends to as much as 8 chain units away from a network junction. This estimate is consistent with the degree of crystallinity measured in various crosslinked PTHF rubbers. The equilibrium melting point for linear PTHF was determined to be 361°K. Although this is significantly higher than previously reported values, the present result is congruent with the melting temperatures measured for crosslinked PTHF, and its use leads to satisfactory predictions of their melting-point depression. The distribution in the lengths of network chains exerted a trivial influence on thermal crystallization behavior. Although this distribution must in principle influence crystallization behavior in so far as it governs crystallizable sequence lengths, differences between uni- and bi-modal network architectures were moderate under the present experimental conditions.

Thermodynamics of Shrinkage of Fibrous (Racked) Rubber

1958 ◽  
Vol 31 (3) ◽  
pp. 485-498
Author(s):  
J. F. M. Oth ◽  
P. J. Flory
Keyword(s):  
Tensile Force ◽  
The Other ◽  
Degree Of Crystallinity ◽  
Melting Point Depression ◽  
Heat Of Fusion ◽  
Γ Radiation ◽  
Melting Temperatures ◽  
The Degree Of Crystallinity ◽  
Heat Of Transformation

Abstract Highly oriented natural rubber samples of Roberts and Mandelkern, prepared by racking and subsequently crosslinked using γ-radiation, undergo a spontaneous shrinkage upon melting which closely resembles the shrinkage of collagen. If the transformation is arrested by application of a tensile force, a state of equilibrium may be established between two distinct zones, or phases, one being totally amorphous (shrunken) and the other unchanged (i.e., racked). Determination of the stress τeq required for phase equilibrium at various temperatures is described. Extrapolation to τeq=0 gives equilibrium melting temperatures Tmi, which are about 8° below the temperatures Tsi for spontaneous shrinkage. The heat of transformation of racked to amorphous rubber calculated from the dependence of τeq on T is 4.5 cal g−1. Since the degree of crystallinity is only 0.24, the heat of fusion calculated for 1 g of crystalline rubber is ca. 19 cal, which agrees satisfactorily with the value 15.3 cal, deduced by Roberts and Mandelkern through use of the melting point depression method. The shrinkage of racked rubber displays all of the important features associated with the similar contraction of fibrous proteins.

scholarly journals Impact of environmental agents on non-woven polylactide/natural rubber agrofiber

2021 ◽  
Vol 285 ◽  
pp. 07034
Author(s):  
Yulia Tertyshnaya ◽  
Maksim Zakharov ◽  
Alina Ivanitskikh ◽  
Anatoliy Popov
Keyword(s):  
Natural Rubber ◽  
Uv Irradiation ◽  
Thermal Characteristics ◽  
Degree Of Crystallinity ◽  
Distilled Water ◽  
Fibrous Materials ◽  
Scanning Calorimetry ◽  
Melting Temperatures ◽  
Environmental Agents ◽  
The Degree Of Crystallinity

In the work an eco-friendly non-woven fiber made of polylactide and natural rubber with a rubber content from 0 to 15 wt.% was obtained by electrospinning. The influence of distilled water and UV irradiation on the agrofibers has been investigated. The water sorption test showed that the addition of natural rubber into the polylactide matrix does not significantly affect the degree of water absorption of the fibrous materials, which is in the range of 49-50.6%. Thermal characteristics after 180 days of degradation in distilled water at 22±2 oC and UV irradiation at a wavelength of 365 nm during 100 hours were determined using the differential scanning calorimetry. Changes in the values for glass transition and melting temperatures, and the degree of crystallinity were determined.

scholarly journals Effect of Heterogeneous Deacetylation on the Properties of Northern Shrimp Chitin and Chitosan

2020 ◽  
Author(s):  
Nataliia Dolgopiatova ◽  
Yuliya Kuchina ◽  
Tatiana Dyakina ◽  
Tatiana Volkova
Keyword(s):  
Molecular Weight ◽  
Shear Stress ◽  
Alkaline Treatment ◽  
Degree Of Crystallinity ◽  
Repeated Treatment ◽  
Experimental Conditions ◽  
Northern Shrimp ◽  
Chitin And Chitosan ◽  
Chitosan Deacetylation ◽  
The Degree Of Crystallinity

The effect of alkaline treatment of shrimp chitin on the molecular weight, the degree of deacetylation and degree of crystallinity of the resulting chitosan is studied. The viscosity of chitosan solutions from repeatedly deacetylated chitin is studied. It is shown that repeated treatment of chitin/chitosan with alkali causes the destruction of polysaccharide macromolecules. After four-time deacetylation and one-time deacetylation of chitin/chitosan for four hours, the molecular weight of the polysaccharide decreases by ten times. The maximum degree of chitosan deacetylation under experimental conditions was 92.0 -92.5%. The diffractograms of chitin and chitosan from the Northern shrimp are of the form typical for samples containing an amorphous phase in addition to a crystalline phase. The degree of crystallinity of chitin from Northern shrimp was 40.8%, of chitosan samples after one-, two-, and three-time deacetylation was 62-65%. For a sample of chitosan obtained after four-time deacetylation, recrystallization, and drying in a freeze dryer, the degree of crystallinity is close to the degree of crystallinity of shrimp chitin. The investigated acetic acid chitosan solutions with a concentration of 5% (wt.) and the chitosan molecular weight of 250, 160 and 130 kDa in their rheological properties are liquid-like non-Newtonian systems, their viscosity decreasing with increasing shear stress. After four-time deacetylation of chitin, the viscosity of chitosan solutions practically does not change with increasing shear stress, which apparently can be due to a significant decrease in the molecular weight of chitosan under these conditions.

Investigating the Effect of Nanoclay Loadings and Re-Processing on the Melting and Crystallization Behavior of PP/Clay Nanocomposites

2019 ◽  
Vol 951 ◽  
pp. 21-25
Author(s):  
Achmad Chafidz ◽  
Sholeh Ma'mun ◽  
Haryanto ◽  
Wara Dyah Pita Rengga ◽  
Prima A. Handayani ◽  
...  
Keyword(s):  
Crystallization Behavior ◽  
Crystallization Process ◽  
The Other ◽  
Degree Of Crystallinity ◽  
Clay Nanocomposites ◽  
Scanning Calorimetry ◽  
Onset Crystallization Temperature ◽  
Significant Difference ◽  
The Degree Of Crystallinity ◽  
Melting And Crystallization

In this study, PP/clay nanocomposites have been fabricated at different nanoclay loadings, i.e. 0, 5, 10, and 5 wt% for the 1stcycle and 2ndcycle (re-processing). The prepared nanocomposites were then characterized by a Differential Scanning Calorimetry (DSC) to investigate the effects of nanoclay loadings and re-processing on the melting and crystallization of the nanocomposites. The DSC results showed that the melting temperature,Tmwas not significantly affected by the nanoclay loadings and re-processing. In the other hand, the degree of crystallinity,Xcof the nanocomposites was higher than that of neat PP, but only reached a maximum at nanoclay loading of 5 wt% (i.e. 51.2% for NC-5-I and 48.3% for NC-5-II). Thereafter, theXcdecreased at higher nanoclay loadings. There was no significant difference inXcbetween 1stcycle and 2ndcycle. Additionally, in all nanocomposites samples for both cycles, there were two crystallization temperatures, i.e.Tc1andTc2. In the overall crystallization process, theTcof nanocomposites increased by 11-12°C compared to that of neat PP. Whereas, the onset crystallization temperature,Tocalso increased by approx. 13°C. Apparently, there was no significant effect of nanoclay loadings and re-processing on theTcndTocof the nanocomposites.

Research of Polyethylene in Products of Autocomponents

2019 ◽  
Vol 946 ◽  
pp. 103-108
Author(s):  
Lenar N. Shafigullin ◽  
Natalia V. Romanova ◽  
Azat T. Gabdrakhmanov
Keyword(s):  
Melting Point ◽  
Quality Assessment ◽  
Automotive Industry ◽  
Complex Geometry ◽  
Performance Characteristics ◽  
Degree Of Crystallinity ◽  
Dsc Analysis ◽  
Modifying Additives ◽  
The Difference ◽  
The Degree Of Crystallinity

Polyethylene is widely used in the production of products for the automotive industry, due to the unique properties and the possibility of manufacturing hollow products of complex geometry. In this work the thermal research of polyethylene in finished productsand the quality assessment of autocomponents materials, depending on the type of polyethylene were conducted. An assessment methodologyof the material of products is suggested, which indicates the difference between the batches of autocomponents products for the acceptance or rejection thisbatch by conducting DSC-analysis. It was found that the products of autocomponents, in particular, "splash-absorbing shield", based on LDPE with a melting point above 110 °C have unsatisfactory performance characteristics. It is shown that modifying additives to improve the elasticity of the LDPE lead to partial the amorphization of PE, that is, a decrease in the degree of crystallinity by 4% relative to the LDPE without additives.

scholarly journals Biodegradable polyesters based on succinic acid

2003 ◽  
Vol 57 (11) ◽  
pp. 526-535
Author(s):  
Marija Nikolic ◽  
Dejan Poleti ◽  
Jasna Djonlagic
Keyword(s):  
Succinic Acid ◽  
Adipic Acid ◽  
Enzymatic Degradation ◽  
Degree Of Crystallinity ◽  
Candida Cylindracea ◽  
Candida Cylindracea Lipase ◽  
Unsaturated Polyesters ◽  
Melting Temperatures ◽  
Degradation Tests ◽  
The Degree Of Crystallinity

Two series of aliphatic polyesters based on succinic acid were synthesized by copolymerization with adipic acid for the first series of saturated polyesters, and with fumaric acid for the second series. Polyesters were prepared starting from the corresponding dimethyl esters and 1,4-butanediol by melt transesterification in the presence of a highly effective catalyst tetra-n-butyl-titanate, Ti(0Bu)4. The molecular structure and composition of the copolyesters was determined by 1H NMR spectroscopy. The effect of copolymer composition on the physical and thermal properties of these random polyesters were investigated using differential scanning calorimetry. The degree of crystallinity was determined by DSC and wide angle X-ray. The degrees of crystallinity of the saturated and unsaturated copolyesters were generally reduced with respect to poly(butylene succinate), PBS. The melting temperatures of the saturated polyesters were lower, while the melting temperatures of the unsaturated copolyesters were higher than the melting temperature of PBS. The biodegradability of the polyesters was investigated by enzymatic degradation tests. The enzymatic degradation tests were performed in a buffer solution with Candida cylindracea lipase and for the unsaturated polyesters with Rhizopus arrhizus lipase. The extent of biodegradation was quantified as the weight loss of polyester films. Also the surface of the polyester films after degradation was observed using optical microscopy. It could be concluded that the biodegradability depended strongly on the degree of crystallinity, but also on the flexibility of the chain backbone. The highest biodegradation was observed for copolyesters containing 50 mol.% of adipic acid units, and in the series of unsaturated polyesters for copolyesters containing 5 and 10 mol.% of fumarate units. Although the degree of crystallinity of the unsaturated polyesters decreased slightly with increasing unsaturation, the biodegradation was not enhanced suggesting that not only the chemical structure and molecular stiffness but also the morphology of the spherulites influenced the biodegradation properties.

scholarly journals Investigation of Thermal Behavior of Layered Double Hydroxides Intercalated with Carboxymethylcellulose Aiming Bio-Carbon Based Nanocomposites

2019 ◽  
Vol 3 (2) ◽  
pp. 55
Author(s):  
Vagner R. Magri ◽  
Alfredo Duarte ◽  
Gustavo F. Perotti ◽  
Vera R.L. Constantino
Keyword(s):  
Layered Double Hydroxides ◽  
Mixed Oxides ◽  
Degree Of Crystallinity ◽  
X Ray Diffraction ◽  
Experimental Conditions ◽  
X Ray ◽  
Vibrational Spectroscopies ◽  
Xrd Patterns ◽  
Double Hydroxides ◽  
The Degree Of Crystallinity

Carboxymethylcellulose (CMC), a polymer derived from biomass, was intercalated into layered double hydroxides (LDH) composed by M2+/Al3+ (M2Al-CMC, M = Mg or Zn) and evaluated as precursors for the preparation of biocarbon-based nanocomposites by pyrolysis. M2Al-CMC hybrids were obtained by coprecipitation and characterized by X ray diffraction (XRD), vibrational spectroscopies, chemical analysis, and thermal analysis coupled to mass spectrometry. Following, pyrolyzed materials obtained between 500–1000 °C were characterized by XRD, Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Above 600 °C, Raman spectra of all samples showed the presence of graphitic carbon, which plays a role in the degree of crystallinity of produced inorganic phases (for comparison purposes, M2Al-CO3 materials were investigated after calcination in the same experimental conditions). XRD patterns of Mg2Al-CMC pyrolyzed between 600–1000 °C showed poorly crystallized MgO and absence of spinel reflections, whereas for Zn2Al-CMC, it was observed well crystallized nanometric ZnO at 800 °C, and ZnAl2O4 and γ-Al2O3 phases at 1000 °C. Above 800 °C, the carbothermic reaction was noticed, transforming ZnO to zinc vapour. This study opens perspectives for nanocomposites preparation based on carbon and inorganic (mixed) oxides through precursors having organic-inorganic interactions at the nanoscale domain.

Influences of the Crystallization Behavior of n-HA Reinforced PA66 Biocomposite on Its Mechanical Properties

2006 ◽  
Vol 510-511 ◽  
pp. 898-901 ◽  
Author(s):  
Xiang Zhang ◽  
Yu Bao Li ◽  
Yi Zuo ◽  
Guo Yu Lv ◽  
Yuan Hua Mu
Keyword(s):  
Mechanical Properties ◽  
Crystallization Behavior ◽  
Annealing Temperature ◽  
Injection Pressure ◽  
Degree Of Crystallinity ◽  
Crystalline Degree ◽  
Close Relationship ◽  
The Degree Of Crystallinity

The crystallization behavior of n-HA/PA66 biocomposites at different processing pressure and annealing temperature were investigated by XRD and DSC. The results showed that increasing annealing temperature would weaken the crystalline intensities of pure PA66 and its composites. For n-HA/PA66 composites, the peaks of α1 crystals of PA66 disappeared, only α2 crystals existed, and with the increase of injection pressure and annealing temperature, the crystalline intensity of PA66 decreased. The degree of crystallinity (Xc) of PA66 in composites increased with the increase of injection pressure, however, annealing temperature had no obvious effects on crystalline degree. The mechanical properties had close relationship with the crystallization behavior of the materials.

Dynamic Mechanical Properties, Crystallization Behavior and Morphology of Nanoscale Tin Fluorophosphate Glass/Polyamide 66 Hybrid Materials

2016 ◽  
Vol 16 (4) ◽  
pp. 4147-4152 ◽  
Author(s):  
Huiwen Liu ◽  
Jing Yang ◽  
Honglin Yu ◽  
Xiaoxuan Zou ◽  
Bo Jing ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Hybrid Materials ◽  
Crystallization Behavior ◽  
Dynamic Mechanical Properties ◽  
Degree Of Crystallinity ◽  
Polyamide 66 ◽  
Dynamic Mechanical ◽  
Fluorophosphate Glass ◽  
Two Phases ◽  
The Degree Of Crystallinity

The dynamic mechanical properties, crystallization behavior and morphology of nanoscale Tg tin fluorophosphate glass (TFP glass)/polyamide 66 (PA66) hybrid materials were investigated by XRD, DSC and SEM. The experimental results showed that the Tg of TFP/PA66 hybrid decreased and the third relaxation in the highly filled hybrid appeared due to the interaction between the TFP glass and amide groups of PA66. The storage modulus of the hybrid materials increased with increase in the content of TFP at low temperatures but had little effect at high temperatures. This result was attributed to the stiffness depression of the TFP glass when the temperature rose above its Tg and the similar elasticity of the two phases because of the interaction between the components. The degree of crystallinity and α, γ crystal content of PA66 both decreased due to the interaction between the two phases. In addition, the phase defect, the size distribution and the compatibility of TFP in the PA66 matrix were discussed by SEM, the results showed that the TFP appeared aggregation partly, but had the favorable compatibility in the PA66 matrix.

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