新产品·新技术信息

胶粘剂和密封剂中所需要的绿色增塑剂

来源：林中祥胶粘剂技术信息网2011年06月15日

阅读次数：次

The Need for Green Plasticizers in Adhesives and Sealants

Extensive research is going on to find alternative plasticizers for medical and other commodity plastics. Several alternatives have been suggested which may eventually find their way into adhesive and sealant formulations. Some of these will offer better compatibility with certain polymers and some will show less migration and leaching tendency. However, the major driving factors for developing alternative plasticizers is greater sustainability through INSERT INTO [lzx].[dbo].[tb_new]([id],[type],[title],[source],[personal],[image],[contents],[time],[number]) VALUES (1) reduced toxicity and INSERT INTO [lzx].[dbo].[tb_new]([id],[type],[title],[source],[personal],[image],[contents],[time],[number]) VALUES (2) the elimination of the use of environmentally harmful raw materials. If successful, these new materials can certainly be considered "green".

This article will first review the requirements for plasticizers in adhesive and sealant formulations and identify the problems that result from the use of conventional plasticizers. The article will then examine some of the development trends toward green plasticizers and recognize new materials that have been or are about to be commercialized.

Mechanism of Plasticization

Plasticizers account for the single largest type of plastic additive. Plasticizers are organic liquids or solids that are incorporated into a compatible polymer to reduce interaction between molecules and improve its molecular mobility. This is primarily accomplished by a lowering of the glass transition temperature, Tg. Benefits of plasticizer incorporation include improvement in flexibility, low temperature performance, softness, and modification of a number of other properties. The various effects that plasticizers have on physical properties are summarized in Table 1.

Plasticizers Can Reduce:	Plasticizers Can Increase:
Modulus Tensile strength Hardness Density Melt viscosity Glass transition temperature Electrostatic chargeability Volume resistivity	Flexibility Elongation at break Toughness Dielectric constant and power factor Softness Impact resistance Low temperature properties

Table 1: Expectations of Plasticizers

The value proposition of using plasticizers depends very much on the type of polymer that is being modified, the form of the resulting product (e.g., waterborne, solvent based, solid, etc.) and the products end-use application. The current market offers numerous choices of plasticizers with a range of attributes that can be selected for specific applications to meet critical material requirements.

Plasticizers are low molecular weight materials that form secondary bonds to polymer chains and spread them apart. In this manner plasticizers reduce polymer to polymer chain attractions and provide more mobility of the polymeric chains. The glass transition temperature is generally lowered by the incorporation of plasticizers.

The degree of plasticization is largely dependent on the plasticizers chemical structure, including chemical composition, molecular weight, and functional groups. Plasticizers that have low molecular weight and a small number of polar groups generally provide higher flexibility and plasticization. Unfortunately, low molecular weight also corresponds to a high degree of migration and volatilization problems that could be associated with health or safety risks.

Almost all types of polymers can be plasticized. However, the plasticizer must be compatible with the base polymer in a formulation to function efficiently. The plasticizer and polymer should have similar polarity to produce compatibility. In addition to compatibility with the base polymer, selection criteria for plasticizers include performance, cost, food contact status, volatile organic emissions, migration potential, and regulatory labeling. Ideally plasticizers should be:

Highly compatible with polymers
Stable in both high and low temperature environments
Sufficiently lubricate over a wide temperature range
Insensitive to solar ultraviolet radiation
Leaching and migration resistant
Inexpensive
Fulfilling of health and safety regulations.

Plasticizers in Adhesives and Sealants

Plasticizers are incorporated into an adhesive formulation generally to provide it with flexibility and/or elongation. Plasticizers can be considered as nonvolatile solvents for the base resin. By being incorporated into the formulation, they separate the polymer chains and enable their movement relative to one another to be more easily accomplished.