Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2000-07-11
2002-08-20
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000, C324S312000
Reexamination Certificate
active
06437565
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining a physical property of a material, particularly of an impact-modified plastic.
Rapid determination of a physical property of a plastic is an important capability for developing new materials, for monitoring manufacturing processes and for trouble-shooting customer service problems. Glass transition temperature, tensile strength, flexural modulus, flexural strength, notched IZOD and heat distortion temperature (HDT) are typically used to characterize performance and applicability of a plastic for a particular use. A number of features pertaining to the molecular structure of a plastic, including molecular weight, composition and chemical bonding affect these physical properties.
For this reason, considerable effort has been applied to develop methods to measure plastic molecular characteristics, particularly of rubber-modified plastics. These plastics are composite materials that comprise a rigid matrix characterized by a relatively high T
g
with a dispersed low T
g
rubbery phase. Composition of matrix and rubber, amount of dispersed rubber, particle size and particle size distribution of the rubber, strength of rubber-matrix adhesion and mechanical relaxation behavior of the rubber all influence the physical properties of these complex materials.
Mechanical relaxation is considered a key variable for optimizing effectiveness of a rubber as an impact modifier. Mechanical relaxation is strongly affected by crosslink density. Crosslink density is a quantitative measure of the number of crosslinks that exist in a given volume in a thermosetting polymer. Insufficiently crosslinked rubbers do not favorably impart toughness to a sufficient level, while over crosslinked rubbers are ineffective at retarding crack propagation.
Crosslink density in a polymer can be determined by pulsed Nuclear Magnetic Resonance (NMR) spectroscopy. Pulsed NMR techniques are used in instruments for the measurement of the type, property and quantity of lattice bound and free, magnetically active nuclei within a sample. Some of the substances and properties that have been measured by NMR techniques are: polymers and copolymers, oils, fats, crystalline materials and moisture, density and melt indices.
Pulsed NMR uses a burst or pulse of energy that is designed to excite the nuclei of a particular species of a sample being measured. the protons, or the like, of such sample having first been preprocessed in an essentially static magnetic field. In other words a precession is modified by the pulse. After the application of the pulse there occurs a free induction decay (FID) of the magnetization associated with the excited nuclei. That is, the transverse magnetization associated with the excited nuclei relaxes back to its equilibrium value of zero.
Several NMR procedures based on spin-spin relaxation time (T
2
) have been developed for this purpose. A. Guthausen et al., “Analysis of Polymer Materials by Surface NMR via the MOUSE,” Journal of Magnetic Resonance 130, 1-7 (1998) used T
2
to measure curing time and aging characteristics of a polyvinylidene difluoride. Füillber et al., “The effect of crosslinking in elastomers investigated by NMR analysis of
13
C edited transverse
1
H NMR relaxation,” Macromolecular Chemistry 197, 581-583 (1996) correlated ′H spin—spin relaxation rate (1/T
2
) to vulcameter torque.
There is a need for a method to measure crosslink density and other material properties in which little or no sample manipulation is required and that can be used at any stage of a manufacturing process
BRIEF SUMMARY OF THE INVENTION
According to the invention, a method is provided that can be used at any stage of a manufacturing process to determine a physical property such as crosslink density. The method requires little or no sample manipulation. The method is independent of rubber particle size and matrix composition. In the method, a physical property of a material is determined by NMR measurement. The method comprises measuring a T
1
(spin lattice relaxation time) for a material, measuring a T
2
(spin-spin relaxation time) for the material and calculating a value T
1
/T
2
representative of a physical property of the material.
In another embodiment, the invention is a method to determine a physical property of a material, comprising deriving a model of a relationship between a physical property and a value T
1
/T
2
of the material, detecting a signal T
1
and a signal T
2
of a sample of the material by NMR and comparing a quotient T
1
/T
2
of the sample to the model to determine a physical property of the material.
In a final embodiment, the invention relates to a system to control a process to synthesize a material. The system comprises a processor, a detector and a comparator. The processor stores a model of a relationship between a physical property and a value T
1
/T
2
of the material. The detector detects a signal T
1
and a signal T
2
of a sample of the material by NMR. The comparator compares a quotient T
1
/T
2
of the sample to the model to determine a physical property of the material.
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patent: 4694252 (1987-09-01), Riederer et al.
patent: 4894416 (1990-01-01), Gallucci
patent: 5375569 (1994-12-01), Santella
patent: 5519319 (1996-05-01), Smith et al.
patent: 5786411 (1998-07-01), Barren et al.
patent: 5994442 (1999-11-01), Fujiguchi et al.
Beall et al (chapter 4) in NMR Data Handbook for Biomedical Applications. Pergamon Press (1984), pp. 32-39.*
“A Guthausen et al., Analysis of Polymer Materials by Surface NMR via the Mouse”, by A. Guthausen et al., Journal of Magnetic Resonance 130, 1-7 (1998).
“The Effect of Crosslinking in Elastomers Investigated by NMR Analysis of 13C Edited Transverse 1H NMR Relaxation, Macromolecular Chemistry, 197, 581-592 (1996)”, Fullber et al,.
Bennett Bernadette Mondragon
Early Thomas Alan
Williams Elizabeth Anne
General Electric Company
Johnson Noreen C.
Lefkowitz Edward
Shrivastav Brij B.
Vo Toan P.
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