Polymer graft modification

Free radical polymerization is a modification technique called “polymer graft modification” that adds polar or functional side groups to the polymer chain. After graft modification, the polymer has exceptionally high polarity or has unique functional groups, which can enhance the polymer’s adhesiveness and printability. It can also be employed as a compatibilizer, a toughener, and a variety of functional materials, among other things.
Melt method, solution method, suspension method, solid phase method, etc. are all examples of polymer graft modification. The melt method is the most popular among them since it can be employed in a twin-screw extruder, costs less money, and is more easily executed.

Polymer graft modification’s function

Numerous novel effects will manifest after the polar functional groups are graft-modified into the polymer. The primary categories of consequences are described below.

1.  Effect of flame retardants 

The main chain or side chains of the polymer are grafted with elements or groups that have flame-retardant properties, converting the polymer into an intrinsic flame-retardant resin.
For instance, adding boron, silicon, sulfur, metal, etc. to the resin can enhance its ability to withstand flames. As an illustration, the oxygen index of PS with a silane graft grew from 18.3% to 20.6%, PS with a boron graft increased from 18.3% to 25.6%, and EVOH with a silane graft increased from 21.8% to 2.1%. When EVOH was grafted with 2.01% boron, the oxygen index rose from 21.8% to 33.2%.

2. The compatibilizer’s function

To increase the resin’s compatibility with other polymers, reactive functional groups are added by a chemical process known as grafting. For polymer alloys, such as polyethylene grafted with maleic anhydride, it can be employed as a compatibilizer. HDPE/PA compatibilizer.

3. Effect of a toughening agent

Although many elastomers themselves have excellent toughening properties, it is challenging to achieve the appropriate toughening effect due to poor compatibility with the toughening matrix resin. This type of elastomer’s compatibility with the toughened matrix resin and toughening efficiency can both be significantly enhanced after graft modification.
For instance, pure POE has a good toughening impact on PP but not so much on PA, mostly due to the poor compatibility between POE and PA; the toughening effect will be enhanced if maleic anhydride is employed for graft modification to generate POE-g-MAH. It becomes the greatest toughening agent for PA and enhances compatibility with PA.
Another illustration is the average toughening impact of pure SEBS on PET and PBT. Because of their poor compatibility, this is the cause. When graft modification with glycidyl methacrylate (GMA) is utilized to create SEBS-g-GMA, PET and PBT are good toughening agents.

Polymer graft modification formula composition

Resin, grafting monomer, initiator, and antioxidant are the main components of the polymer’s grafting formula.

(1) Resin

The fundamental component of grafting is resin, and popular types include PP, HDPE, LDPE, LLDPE, EVA, PS, and EPDM.

2) Creating monomer

This graft is the monomer. They are usually organic substances that are acidic or alkaline, such as methane, maleic anhydride (MAH), acrylic acid (AA), and its derivatives, methacrylic acid (MMA), unsaturated fatty acids, and methylene succinic acid. The following substances are waiting: vinyl silane, unsaturated silane, butyl acrylate, ethyl acrylate, glycidyl acrylate, oleic acid, and vinyl acetate.
The grafting efficiency often decreases with the length of the grafting monomer’s chain. Maleic anhydride, which possesses highly reactive double bonds and does not easily self-polymerize under processing conditions, is the most widely employed grafting monomer. The amount of monomer added is typically around 1%, although it can potentially be raised to meet the needs of the specific application. The maximum amount of addition is 20%.
It is occasionally required to add a second monomer to boost grafting rate and decrease risk of side effects. Styrene, acrylamide, acrylate, etc. are among the components of the second monomer. The grafting efficacy of a single monomer is particularly low for GMA grafting, necessitating the addition of a second styrene monomer and occasionally an electron donor, such as dimethylsulfoxide, dimethylacetamide, etc.

(3)Initiator

The function of the initiator is to initiate the reaction between the grafting monomer and the resin, specifically benzoyl peroxide (BPO), dicumyl peroxide (DCP), 2,3-dimethyl 2,3-diphenylbutane alkane (DMDPB), acrylamide (AM), 2,5-di-tert-butyl peroxy-2,5-dimethyl 3-acetylene (LPO) and 1.3-di-tert-butyl peroxyisoacene, etc. Typically, the addition amounts to 0.1%.
A novel class of initiator is DMDPB. Although its starting effectiveness is lower than that of BPO and DCP, it has the advantages of a high decomposition temperature and relatively stable free radicals, which lessen the likelihood that grafts may cross-link to produce macromolecular gels. During processing, the grafted product won’t appear gel-like or contain little gel.
The use of composite initiators has been researched recently. The grafting rate, for instance, doubles when DCP:BPO=1:1 is applied. For instance, the grafting effect is substantially better when undecanoic acid is double-initiated with DCP and BPO than when it is used alone.
Different resins are suited for different initiators in the given selection. For instance, when DCP is employed as the initiator for PP, there are significant side effects and a high level of degradation. However, PP will only degrade somewhat if BPO is employed as the initiator, and it will change significantly as the initiator concentration rises. few. In general, DCP initiator is utilized while grafting GMA monomer.

(4)Antioxidants

Antioxidants are mostly added to readily degradable resins like PP and ABS in order to inhibit degradation reactions during the grafting reaction. Antioxidant 1010 and other specific types are included, and the addition is roughly 0.5%.
Composite grafting technology, which includes attaching two or more monomers to a resin to create a multi-monomer graft with improved performance, has been developed recently. For instance, introducing the second monomer styrene can efficiently limit the degradation of PP and increase the grafting effect of MAH or GMA when grafting PP with MAG or GMA.