Carboxylated Ethylene Polymer Blends via Solid-Phase Grafting
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Solution Overview
Problem
The existing methods for manufacturing carboxylated ethylene polymers as adhesion promoters in plastic-metal composites are costly due to high molecular weights and residual monomer removal challenges, especially in melt-grafting processes, which affect their performance and economic viability.
Innovation Solution
A two-step process involving solid-phase grafting of carboxyl monomers onto low-molecular-weight ethylene polymers followed by melt-grafting with unmodified high-molecular-weight ethylene polymers and olefinic elastomers, using specific radical initiators and reaction conditions to achieve a carboxylation degree of 0.5-1 wt.%, resulting in a blend suitable for adhesion promotion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If melt-grafting is used to manufacture carboxylated ethylene polymers, then adhesion promoter properties are achieved, but manufacturing costs increase due to high molecular weights and residual monomer removal challenges
Solution Approach 1:
The patent divides the manufacturing process into two distinct stages: (1) solid-phase grafting of carboxyl monomers onto low-molecular-weight ethylene polymer to achieve carboxylation degree of 0.5-1 wt.%, and (2) blending with unmodified high-molecular-weight ethylene polymers. This segmentation allows each stage to be optimized independently, reducing overall manufacturing complexity and cost while maintaining adhesion promoter properties.
Solution Approach 2:
The patent changes the molecular weight parameter of the polymer substrate by using low-molecular-weight ethylene polymer (MFR ≥ 20 g/10 min) for the grafting stage, which facilitates faster diffusion rates and higher graft polymerization rates. After carboxylation, the modified polymer is blended with high-molecular-weight ethylene polymers to achieve the desired final molecular weight and viscosity characteristics, thereby optimizing both manufacturing efficiency and product performance.
2Strength
If high-molecular-weight ethylene polymers are used in melt-grafting, then adhesion strength is improved, but residual monomer removal becomes more difficult and costly
Solution Approach 1:
The patent performs preliminary carboxylation of low-molecular-weight ethylene polymer in the solid phase before blending with high-molecular-weight polymers. This preliminary action ensures that the carboxyl groups are already attached to the polymer backbone, and subsequent blending does not introduce additional monomers that would require removal, thereby eliminating the residual monomer removal problem while maintaining high adhesion strength.
3Ease of manufacture
If solid-phase grafting is performed below melting point, then manufacturing cost is reduced, but polymer dissolution and solvent separation become costly
Solution Approach 1:
The patent extracts the solvent separation step entirely from the process by performing solid-phase grafting without adding solvents. The carboxyl monomers are grafted directly onto the solid ethylene polymer particles in the melt state, and the modified polymer is then blended with unmodified polymers. This extraction of the solvent step eliminates the need for costly polymer dissolution and solvent separation operations while maintaining manufacturing cost efficiency.
4Productivity
If low-molecular-weight ethylene polymers are used for carboxylation, then graft polymerization rate increases, but final blend viscosity may be insufficient
Solution Approach 1:
The patent merges two polymer components with complementary properties: low-molecular-weight carboxylated ethylene polymer (providing high graft polymerization rate and adhesion promoter functionality) and unmodified high-molecular-weight ethylene polymer (providing appropriate viscosity and processing characteristics). The synergistic combination of these components achieves both high productivity in the grafting stage and sufficient blend viscosity in the final product.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces costs and enhances the adhesion strength of the carboxylated ethylene polymer blends, maintaining high peel strengths even after long annealing, while optimizing molecular weights and simplifying the removal of residual monomers.
Implementation Method 1
graft-polymerizing at reaction temperatures of 30-120° C. for 5-120 min... in the presence of a radical-forming peroxidic initiator
Implementation Method 2
by grafting a carboxyl group-containing monomer such as acrylic acid, fumaric acid and especially, maleic acid anhydride, onto the olefinic backbone-polymer
Implementation Method 3
continuously feeding into a reaction extruder 100 pbw of the modified ethylene polymer obtained in the 1st, solid phase step, together with 150-4,000 pbw of an unmodified ethylene polymer or polymer blend
Data Source
AI summary
Procedure for the manufacture of carboxylated ethylene polymer blends, in which in a 1st step, in a fluid mixing reactor, to 100 pbw of a particulate ethylene polymer—chosen from among ethylene homopolymers (HDPE, LDPE) and/or linear ethylene copolymers with 2 to ≦̸20 wt.-% polymerized-in C3-12-olefin units (LLDPE, EOP), with a melt-flow rate MFR (190° C./2.16 kg)≧20 g/10 min—are added 0.05-15 pbw of a α,&bgr;-ethylenically unsaturated mono and/or dicarboxylic acid or its anhydride (carboxyl monomer), or a monomer mixture containing at least one carboxyl monomer and 0.01-10 pbw of a radical initiator or initiator mixture, and graft-polymerizing at reaction temperatures of 30-120° C., over a reaction time of 5-120 min and subsequently, in a 2nd step, reacting a mixture continuously fed into a reaction extruder of 100 pbw of the modified ethylene polymer obtained in the 1st solid phase step, 150-4,000 pbw of an ethylene polymer or polymer blend with a melt flow rate MFR (190° C., 2.16 kg)<20 g/10 min, as well as 0-4,000 pbw of an olefinic elastomer, at temperatures of 160-260° C. and continuously removing the graft-modified ethylene polymer blend that has a degree of carboxylation of 0.05-1 wt.-%. The products obtained are especially suitable as adhesion promoters and/or adhesives for numerous substrates, preferably on and between metallic surfaces.