A Re-examination of the Relation between the Melting Temperature and the Crystallization Temperature: Linear Polyethylene

1995 ◽  
Vol 28 (9) ◽  
pp. 3205-3213 ◽  
Author(s):  
Rufina G. Alamo ◽  
Brent D. Viers ◽  
L. Mandelkern
Keyword(s):  
Melting Temperature ◽  
Crystallization Temperature ◽  
Linear Polyethylene

On the morphology of melt-crystallized polyethylene - II. Lamellae and their crystallization conditions

1981 ◽  
Vol 377 (1768) ◽  
pp. 39-60 ◽  
Keyword(s):  
Molecular Mass ◽  
Crystallization Temperature ◽  
Lamellar Thickness ◽  
Kinetic Regime ◽  
Secondary Nucleation ◽  
Constant Multiple ◽  
Linear Polyethylene ◽  
Simple Assumption ◽  
Crystallization Conditions ◽  
Prevalent Form

The microstructure of melt-crystallized linear polyethylene has been correlated with the variables of crystallization for most readily attainable conditions. All samples are filled with well defined lamellae with an aver­age chain inclination of about 35° to lamellar normals. The lamellar thickness depends upon supercooling rather than directly on crystalliza­tion temperature, which indicates that it is a kinetically determined quantity. The simple assumption that it is a constant multiple of the height given by secondary nucleation is, however, incorrect. Lamellar profiles depend only upon the crystallization temperature and molecular mass of the polyethylene concerned. They are independent of the extent of spherulitic development and are not determined solely by the kinetic régime in which crystals grow. Dominant S-shaped lamellae (Ss) and their associated subsidiary platelets are, nevertheless, the prevalent form for crystallization within régime II, i. e. in most cases of practical import­ance. The distinction between dominant and subsidiary lamellae is linked to fractional crystallization. At low supercoolings it is shown that shorter molecules are concentrated within subsidiary lamellae, and the trend to separate later-crystallizing species is likely to persist, to a lesser degree, even to quenched samples. With the use of added branched molecules this has been demonstrated to occur. The consequences of spatial segre­gation are likely to include increased vulnerability to mechanical and environmentally induced failure.

scholarly journals Melting temperature versus crystallinity: new way for identification and analysis of multiple endotherms of poly(ethylene terephthalate)

2020 ◽  
Vol 27 (12) ◽  
Author(s):  
Ferenc Ronkay ◽  
Béla Molnár ◽  
Dóra Nagy ◽  
Györgyi Szarka ◽  
Béla Iván ◽  
...  
Keyword(s):  
Melting Temperature ◽  
Crystallization Temperature ◽  
Ethylene Terephthalate ◽  
Primary Crystallization ◽  
Crystallization Time ◽  
X Ray Diffraction ◽  
Molecular Weights ◽  
Poly Ethylene Terephthalate ◽  
Poly Ethylene ◽  
Peak Set

AbstractPoly(ethylene terephthalate) (PET) materials with different molecular weights were isothermally crystallized from melt by systematically varying the temperature and duration of the treatment performed in the differential scanning calorimeter (DSC). Multiple endotherm peaks were observed on the subsequent heating thermograms that were separated from each other on the basis of their melting temperature versus crystallization temperature and melting temperature versus crystallinity function. By this new approach five sub-peak sets were identified and then comprehensively characterised. Wide-Angle X-Ray Diffraction (WAXD) analyses revealed that the identified sub-peak sets do not differ in crystalline forms. By analysing the crystallinity and the melting temperature of the sub-peak sets as a function of crystallization time, crystallization temperature and intrinsic viscosity, it was concluded that below the crystallization temperature of 460 K the sub-peak sets that were formed during primary or secondary crystallization transform partially or completely to a third sub-peak set during the heating run of the measurement, while above this temperature, the sub-peak set formed during primary crystallization gradually transforms to a more stable structure, with higher melting temperature. These formations and transformations are described with mathematically defined parameters as well.

Grain Refinement Mechanism in Undercooled Cu30Ni70

1997 ◽  
Vol 12 (4) ◽  
pp. 873-876 ◽  
Author(s):  
J. Z. Xiao ◽  
K. K. Leung ◽  
H. W. Kui
Keyword(s):  
Grain Size ◽  
Grain Refinement ◽  
Melting Temperature ◽  
Crystallization Temperature ◽  
Rapid Decrease ◽  
Composition Analysis ◽  
Narrow Temperature Range ◽  
Ni Content ◽  
Refinement Mechanism ◽  
Kinetic Crystallization

When undercooled molten Cu30Ni70 crystallizes at an undercooling ΔT≅ 145 K (ΔT is defined as Tl – Tk where Tl is the liquidus of Cu30Ni70 and Tk is the kinetic crystallization temperature), its grain size undergoes a rapid decrease by as much as two orders of magnitude in a narrow temperature range. This phenomenon is termed grain refinement. It was found that grain refinement is brought about by multiplication of dendrites. Composition analysis of the dendrite indicates that it has the least Ni concentration at its axis. The Ni content then increases radially from the central axis. Therefore, the dendrite is unstable against melting since the melting temperature of Cu–Ni increases with Ni content. The origin of grain refinement is attributed to the remelting of these dendrites.

Crystallization Behavior of Polypropylene/Syndiotactic1,2-Polybutadiene Blends

2012 ◽  
Vol 531-532 ◽  
pp. 182-185
Author(s):  
Xiao Feng He ◽  
Shuai Wang ◽  
Tie Jun Ge ◽  
Xue Quan Zhang ◽  
Chun Yu Zhang
Keyword(s):  
High Temperature ◽  
Melting Temperature ◽  
Crystallization Temperature ◽  
Crystallization Behavior ◽  
Strong Impact ◽  
Crystallization Behaviors ◽  
Supercooling Temperature ◽  
Melting And Crystallization

The melting and crystallization behaviors of Polypropylene/Syndiotactic1,2-polybutadiene (PP/s-PB) blends and neat PP were studied by using DSC, the results showed that the presence of s-PB in PP would have a strong impact on the crystallization capacity of PP. The presence of s-PB in PP could increase the crystallization temperature(Tc) of PP, and the s-PB could obviously lower supercooling temperature(Tm-Tc) of PP, but the s-PB in PP have a Slightly influence on the melting temperature(Tm) of PP. The proposed reason for those are that the crosslinking s-PB in high temperature is a nucleator for PP’s crystallization and increases PP’s crystalline rate. However, the s-PB lowers PP’s crystallinity. At the same time, the presence of PP in blends lowers s-PB’s crystallinity, but the PP in blends have a Slightly influence on the melting temperature(Tm) and crystallization temperature(Tc) of s-PB.

scholarly journals Effect of 1,4-Naphthalenedicarboxylic Acid Derivative on Crystallization and Performances of Poly(L-lactide)

2021 ◽  
Vol 58 (1) ◽  
pp. 57-68
Author(s):  
Lisha Zhao ◽  
Jun Qiao ◽  
Xueling Shan ◽  
Yanhua Cai ◽  
Jie Zhang
Keyword(s):  
Thermal Decomposition ◽  
Melting Temperature ◽  
Crystallization Temperature ◽  
Crystallization Rate ◽  
Decomposition Temperature ◽  
Organic Additive ◽  
Onset Crystallization Temperature ◽  
Nucleation Sites ◽  
Biodegradable Poly

In this work, biodegradable Poly(L-lactide) (PLLA) was modified through adding a new organic additive N, N -bis(benzoyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NABH). A comparison on crystallization of the pure PLLA and PLLA/NABH revealed that the NABH as effective heterogeneous nucleation sites enhanced PLLA𠏋 crystallization, and an increase of NABH loading was able to further accelerate crystallization rate of PLLA; whereas a faster cooling rate was not conducive to PLLA𠏋 crystallization, but the appearance of obvious crystallization peak upon cooling at 30şC/min confirmed the advanced enhancing role of NABH for PLLA crystallization again. The investigation on influence of the final melting temperature on the crystallization behavior of PLLA showed that the 170 şC was optimum final melting temperature for enhancing crystallization, even the onset crystallization temperature of PLLA/NABH were higher than 150şC. The melting processes of PLLA/NABH after different crystallization not only could reflect the previous crystallization, but also depended on crystallization temperature and heating rate. Thermal decomposition results showed that the existence of NABH slightly weakened thermal stability of PLLA, and the maximum difference in onset thermal decomposition temperature was only 9.4şC comparing with the pure PLLA. However, the presence of NABH in PLLA matrix seriously weakened optical property.

Investigation of the Thermal Properties of Different Grades Polyamide 12 (PA12) in Improving Laser Sintering Process (SLS)

2014 ◽  
Vol 548-549 ◽  
pp. 294-296 ◽  
Author(s):  
Yusoff Way ◽  
D.T. Pham ◽  
K.D. Dotchev
Keyword(s):  
Glass Transition ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Melting Temperature ◽  
Crystallization Temperature ◽  
Selective Laser Sintering ◽  
Laser Sintering ◽  
Sintering Process ◽  
Melt Flow Rate

Selective Laser Sintering (SLS) is a combined technology of computer and laser to produce complex 3D prototypes directly from CAD modeling. One of the main advantages of employing this technology is that the non-sintered powder can be recycled and reused for another fabrication. However, the fabricated part could be affected by rough and unacceptable surface texture. As a result, the parts may have to be scrapped and the build has to be repeated with a higher ratio of new material. This paper presents an experimental study of the thermal properties of new and recycled of PA12 powder in the Laser Sintering process. The influence of melting temperature, glass transition temperature and crystallization temperature on these properties is investigated. The experimental results have shown that PA12 powder with high melt flow rate, low melting temperature, low glass transition temperature and low degree of crystallization temperature could improve the sintering process.

scholarly journals Thermal Properties of Wood-Plastic Composites with Different Compositions

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 881 ◽  
Author(s):  
Yong Guo ◽  
Shiliu Zhu ◽  
Yuxia Chen ◽  
Dagang Li
Keyword(s):  
Low Temperature ◽  
Melting Temperature ◽  
Dimensional Stability ◽  
Crystallization Temperature ◽  
Wood Fiber ◽  
Linear Thermal Expansion ◽  
Fiber Content ◽  
Wood Plastic Composites ◽  
Degradation Temperature ◽  
Plastic Composites

The thermal performance of wood–plastic composites (WPCs) with different fiber, different fiber contents, and different lubricants were investigated in this paper. The results show that the thermal degradation temperature, melting temperature, crystallization temperature, crystallinity, and viscosity of WPCs with wood fiber were slightly higher than those of WPCs with floor sanding powder and rice husk. As the wood fiber content increased, the melting temperature and crystallinity of WPCs decreased while the crystallization temperature, viscosity, and pseudoplasticity increased. When the wood fiber content was increased to 60%, the dimensional stability of WPCs tended to be constant, and a higher wood fiber content was not conducive for processing of WPCs. WPCs had a small coefficient of linear thermal expansion at low temperature and demonstrated a good dimensional stability. The presence of lubricant reduced the viscosity and increased the pseudoplasticity of the WPCs, which is advantageous for the dimensional stability of WPCs at low temperature while making it worse for high temperatures.

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