Wood sizing agents for PVC composites
Disclosed herein is a process for improving mechanical properties and thermal stability of composites of poly(vinyl chloride) and at least one natural fiber comprising including in said composite an agent comprising a polymer or copolymer comprising at least one alkali metal salt of at least one polymerized ethylenically unsaturated carboxylic acid. Articles of manufacture comprising the stabilized PVC are also disclosed.
1. A process for providing composites of PVC and wood fiber having improved mechanical properties and thermal stability comprising the steps of:
(A) dissolving a sizing agent comprising a polymer or copolymer comprising at least one alkali metal salt of at least one polymerized ethylenically unsaturated carboxylic acid in water to form an aqueous solution of the sizing agent;
(B) adding wood fibers to the aqueous solution formed in (A);
(C) separating and drying the wood fiber to a water content below 1%, whereby a coating of the water soluble sizing agent is formed on the surface of the wood fibers;
(D) combining the sized wood fibers of (C) with PVC at elevated temperature to form composites comprising the sized wood fiber dispersed in a matrix of PVC having improved mechanical properties and thermal stability;
wherein said polymer or copolymer is selected from the group consisting of alkali metal salts of:
(1) poly(acrylic acid), poly(methacrylic acid), poly(crotonic acid), poly(maleic acid), or mixtures thereof; and
(2) copolymers of acrylic acid, methacrylic acid, crotonic acid, or maleic acid with a comonomer selected from the group consisting of acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, acrylic acid esters, methacrylic acid esters, and styrene.
2. The process of claim 1 wherein the polymer or copolymer is selected from the group consisting of alkali metal salts of poly(acrylic acid), poly(methacrylic acid), poly(crotonic acid), poly(maleic acid), and mixtures thereof.
3. The process of claim 1 wherein the sizing agent is a copolymer of an alkali metal salt of acrylic acid, methacrylic acid, crotonic acid, or maleic acid with a comonomer selected from the group consisting of acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, acrylic acid esters, methacrylic acid esters, and styrene.
4. The process of claim 1 wherein the wood fiber is selected from the group consisting of wood flour and sawdust.
5. The process of claim 4 wherein the wood fiber is wood flour.
6. The process of claim 1 wherein the polymer or copolymer is selected from the group consisting of alkali metal salts of poly(acrylic acid), poly(methacrylic acid), and poly(acrylamide co acrylic acid).