Handbook of Curatives and Crosslinkers

George Wypych

• Publisher: ChemTec Publishing
• Year: 2019
• Print ISBN:
  9781927885475
• eBook ISBN:
  9781927885482
• Topic: Physical Sciences
• Subtopic: Mechanics

Handbook of Curatives and Crosslinkers presents the mechanisms of action of these additives, methods of their use, their effects on properties of transformed products, and their applications. Chapters cover the common use of curatives in many industrial products manufactured in large scale, such as adhesives, sealants, coatings, inks, explosives, propellants and foams, and in emerging products, such as optoelectronics, shape-memory applications, light-emitting diodes, and more. In addition, crosslinkers used in typical industrial processing methods, such as solar cells, vulcanization, adhesives, foams and roofing are covered. Each section presents the effect of the additive, including an evaluation of its chemical and physical properties. - Covers the use of curatives in emerging products, such as optoelectronics, shape-memory applications, light-emitting diodes, liquid crystal displays, self-healing materials, etc. - Presents emerging applications, such as drug release, artificial muscles in microdevices, autonomous shape-memory actuators, hygienic textiles, membranes, scaffolds, recycling, sensors, tissue adhesives, wound dressing, and many more

1

INTRODUCTION

According to the standard definition, the crosslinker is an additive which links two polymer chains by the covalent or ionic bond. In polymer chemistry, the curing reaction changes mechanical properties or viscosity by increasing molecular weight of a polymer by reacting two different components. Components can be polymers, prepolymers, oligomers, or monomers. If the components to be linked are polymers, there is no visible difference between curing or crosslinking. For this reason, both terms are frequently interchangeable in meaning and application. If the components have lower molecular weight (e.g., monomer, oligomer) then two different kinds of curatives are typically used, namely chain extenders and/or crosslinkers.

The chain extender has two functional groups divided by a spacer which may be used to regulate hardness of the resultant material, and the crosslinker has the functionality of three or more by which it can react with more than two monomers or prepolymers thus forming a crosslink. Polyurethane chemistry provides still another useful example. Typically, hydroxyl or amine groups react with the isocyanate groups to build a high molecular weight polymer. But in this case, either group may become crosslinker (either isocyanate, or amine, or hydroxyl containing moiety may have more than two functional groups thus playing a role of crosslinker).

In the area of commercial curatives and crosslinkers, the chemical composition of the product is usually unknown as well as the curing mechanism is frequently not disclosed, therefore distinguishing between curatives and crosslinkers is generally difficult if possible and often does not provide any benefits for the selection of these additives. The commercial additives are targeted by their manufacturers to perform under specific compositional constraints. Mainly, the reactivity of components (the material to be cured and the curing moiety) has the primary importance in their selection. For this reason, throughout Databook of Curatives and Crosslinkers, which is a companion book containing information on the commercial products used to increase the molecular weight of polymers, the terms curative and crosslinker are used interchangeably mostly to reflect the naming system adopted by their manufacturers. The curatives/crosslinkers were organized in Databook of Curatives and Crosslinkers according to the alphabetical order of their commercial or chemical names.

In this book, the goal is to discuss the scientific background of curing and crosslinking reactions, therefore, both types of reactions will be discussed in separate chapters including their chemical compositions and properties based on data provided by manufacturers and presented by the authors of scientific publications, their applications to different polymers and the best selection for particular polymer, conditions of reaction and their effect on final product, effect of various additives on the properties of different polymers, and applications in different manufactured products.

In spite of the fact that most scientists agree that the results of crosslinking and curing are similar in the sense that molecular weight of polymer increases and a network is formed, authors of the majority of scientific papers distinguish between both processes and indicate their naming preference. In this book, we will follow nomenclature suggestions of authors of published articles, even though it may sometimes lead to overlaps between applications as curatives or crosslinkers.

In this book, we will attempt to present objective scientific information on the mechanisms characterizing typical crosslinking and curing reactions and list a variety of available options for the modification of different resins showing potential benefits of the process and the effect of conditions under which reactions are performed.

2

CROSSLINKERS

2.1

CHEMICAL COMPOSITION AND PROPERTIES

Table 2.1 shows the averages of the typical properties of crosslinkers based on data given by their manufacturers and presented in scientific publications.

Table 2.1

Typical properties of crosslinkers.

GENERAL INFORMATION
Chemical components: aziridine, carboxylic acids, dicumyl peroxide, fatty acid trimer, hydrogenpolysiloxane, isocyanate, modified inorganic fillers, N,N’-methylenebisacrylamide, organic peroxide, oxime silane, pentaerythritol derivative, peroxyketal, polyamide-epichlorohydrin, polyaziridine, polycarbodiimide, polydimethylsiloxane, polyrotaxane, polythiol, silane, sodium tetraborate, titanate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, trismaleimide, zirconate
Molecular weight: 148-1394	Average functionality: 2.5-3.3	Solids content, wt%: 12-100
Active oxygen content, %: 2.06-11.17		NCO content, %: 30.5-33.5
Ti content, %: 3.3-20.5
PHYSICAL DATA
Color: colorless, white, yellow, brown, blue, red		State: liquid, paste, or solid
Odor: odorless, amine, aromatic, ether, menthol, solvent
Acid number, mg KOH/g: 1-25		pH: 2-11.5
Activation energy, kcal/mol: 36.8-38.1		Density, kg/m^3: 800-1630
Boiling point, °C: 17->390	Melting/freezing point, °C: 235 to -70
Glass transition temperature, °C: -5 to -10		Vapor density: 1-11.7
Half life: 1 min/140-193°C to10 h/99-131°C
Refractive index: 1.384-1.5675
Solubility: acetone, benzene, butanol, chloroform, diethyl ether, dioxane, DMF, DSMO, ethanol, ethyl acetate, hydrocarbons, isopropanol, methanol, methyl ethyl ketone, n-heptane, toluene, water, xylene
Vapor pressure, kPa @20°C: 1.7E-07 to 3.86
Viscosity, mPa s @20°C: 5.7 to 9000
HEALTH & SAFETY
Autoignition temperature, °C: 220-600		Flash point, °C: 6-290
HMIS: Fire: 0-4; Health: 0-3; Reactivity: 0-3
NFPA: Flammability: 0-3; Health: 0-3; Reactivity: 0-2
Carcinogenicity: IARC, NTP, OSHA: No component of this product present at level greater than or equal to 0.1% is identified as probable, possible, or confirmed human carcinogen; to suspected carcinogen
Mutagenicity: none to suspected to category 1B
Teratogenicity: none to category 1A
Explosive concentration, %: LEL: 1.4-2; UEL: 7-19.9
LC50: Inhalation-rat, ppm: >5->800; Dermal-rabbit, mg/kg: >1000-12800; Oral-rat, mg/kg: 390->7000
UN/NA class: 1219, 1263, 1760, 1824, 1933, 3077, 3082, 3101, 3103, 3105, 3106, 3107, 3108, 3110, 3335
UN risk phrases: R10,R20,R21/22,R22,R36/38,R38, R41,R43,R52/53,R68
UN safety phrases: S7,S17,S26,S27,S35, S36/37/38,S44,S47
ECOLOGICAL PROPERTIES
Aquatic toxicity, EC50, mg/l: Algae: 0.8->100/72H, Bluegill sunfish: >603->1000; Daphnia magna: 0.31->1000/48H; Fathead minnow: 6.32-40; Zebra fish: 1.6->1000
Bioaccumulation: not expected to low
Bioconcentration factor, BCF: 6.49-839
Partition coefficient, log Kow: 2.2-7.3
APPLICATIONS
Recommended for resins: ABS, acrylamide, acrylics, alkyd, biopolymers, bromobutyl rubber, butyl rubber, carboxymethyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, chlorinated polyethylene, chloroprene, cyanoacrylate, epoxidized natural rubber, EPDM, epoxy, EVA, fluoroelastomers, guar, high impact polystyrene, hydrogenated nitrile rubber, natural rubber...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Chapter 1: INTRODUCTION
• Chapter 2: CROSSLINKERS
• Chapter 3: CURATIVES
• INDEX