Document:

<PAGE>
                                                                Exhibit 10.20(b)

                                                                  CONFORMED COPY

                                 FIRST AMENDMENT
                                       TO
                           RECEIVABLES SALE AGREEMENT

            THIS FIRST AMENDMENT TO RECEIVABLES SALE AGREEMENT, dated as of
March 18, 2003 (this "Amendment") is entered into by and among ARCH CHEMICALS,
INC. ("Arch") and certain affiliates of Arch listed on the signature pages
hereto (each such affiliate, together with Arch, being the "Originators") and
ARCH CHEMICALS RECEIVABLES CORP. (the "Buyer").

                                    RECITALS:

            WHEREAS, the Originators and Buyer have entered into the Receivables
Sale Agreement (the "Agreement") dated as of March 19, 2002;

            WHEREAS, the parties hereto desire to amend the Agreement in certain
respects as provided herein;

            NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein, the Originators and Buyer hereby agree as follows:

      SECTION 1. Amendments.

The Agreement is hereby amended as follows:

            The definition of "Receivable" in Exhibit I to the Agreement is
hereby amended by adding the following phrase at the end of the first sentence
thereof and before the period:

                        "; provided, however, that in each case the Obligor of
            such indebtedness or other obligation is domiciled in the United
            States of America or in Canada (excluding the Provinces of Quebec,
            New Brunswick, Nova Scotia and Newfoundland)"

      SECTION 2. Reference to and Effect on the Agreement and the Related
Documents.

      Upon the effectiveness of this Amendment, (i) each of the Seller Parties
hereby reaffirms all representations and warranties made by it in Article II of
the Agreement (as amended hereby) and agrees that all such covenants,
representations and warranties shall be deemed to have been remade as of the
effective date of this Amendment, (ii) each of the Seller Parties hereby
represents and warrants that no Termination Event, Amortization Event or
Unmatured Amortization Event shall have occurred and be continuing and (iii)
each reference in the Agreement to "this Agreement", "hereunder", "hereof",
"herein" or words of like import shall mean and be, and any references to the
Agreement in any other document, instrument or

<PAGE>

agreement executed and/or delivered in connection with the Agreement shall mean
and be, a reference to the Agreement as amended hereby.

      The Seller hereby agrees that in addition to any costs otherwise required
to be paid pursuant to the Transaction Documents, the Seller shall pay all
reasonable legal fees and out-of-pocket expenses of the Agent's counsel, Hunton
& Williams, and all audit fees and due diligence costs incurred by the Agent in
connection with the consummation of this Amendment.

      SECTION 3. Effectiveness and Effect.

      This Amendment shall be effective on the day (the "Amendment Effective
Date") on which the last to occur of the following: (i) execution by the Seller
Parties of this Amendment; (ii) execution of the Third Amendment to the
Receivables Purchase Agreement, dated as of the date hereof, by each of the
parties thereto; (iii) execution of the Amended and Restated Fee Letter, dated
the date hereof, by each of the Seller Parties and (iv) payment of all amounts
required to be paid to the Agent on the Amendment Effective Date under the
Amended and Restated Fee Letter. Except as otherwise amended by this Amendment,
the Agreement shall continue in full force and effect and is hereby ratified and
confirmed.

      SECTION 4. Governing Law.

      This Amendment will be governed by and construed in accordance with the
laws of the State of New York.

      SECTION 5. Severability.

      Each provision of this Amendment shall be severable from every other
provision of this Amendment for the purpose of determining the legal
enforceability of any provision hereof, and the unenforceability of one or more
provisions of this Amendment in one jurisdiction shall not have the effect of
rendering such provision or provisions unenforceable in any other jurisdiction.

      SECTION 6. Counterparts.

      This Amendment may be executed in one or more counterparts, each of which
shall be deemed to be an original, but all of which together shall constitute
one and the same instrument. Delivery of an executed counterpart of a signature
page by facsimile shall be effective as delivery of a manually executed
counterpart of this Amendment.

                                       -2-

<PAGE>

        IN WITNESS WHEREOF, the parties have caused this Agreement to be
executed by their respective officers thereunto duly authorized, as of the date
first above written.

                                        ARCH CHEMICALS RECEIVABLES CORP.,
                                        as the Buyer

                                        By: /s/ W. Paul Bush
                                            ----------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH CHEMICALS, INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                            ----------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH SPECIALTY CHEMICALS, INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                            -----------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH CHEMICALS SPECIALTY PRODUCTS, INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                           ------------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH ELECTRONIC CHEMICALS, INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                           -----------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

<PAGE>

                                        ARCH WOOD PROTECTION INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                           -----------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH PERSONAL CARE PRODUCTS, L.P.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                           -----------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        [end of signatures]<PAGE>
                                                                Exhibit 10.20(j)

                                                                  CONFORMED COPY

                             OMNIBUS AMENDMENT NO. 1
                                       TO
                         RECEIVABLES SALE AGREEMENT AND
                         RECEIVABLES PURCHASE AGREEMENT
                       (Arch Chemicals Receivables Corp.)

            THIS OMNIBUS AMENDMENT NO. 1 TO RECEIVABLES SALE AGREEMENT AND
RECEIVABLES PURCHASE AGREEMENT is entered into as of June 25, 2003, by and among
ARCH CHEMICALS, INC. ("Arch"), CERTAIN AFFILIATES OF ARCH LISTED ON THE
SIGNATURE PAGES HERETO (each such affiliate, together with Arch, being,
individually, an "Originator" and, collectively, the "Originators"), ARCH
CHEMICALS RECEIVABLES CORP. (the "Seller"), BLUE RIDGE ASSET FUNDING
CORPORATION, THE LIQUIDITY BANKS FROM TIME TO TIME PARTY TO THE CREDIT AND
SECURITY AGREEMENT and WACHOVIA BANK, NATIONAL ASSOCIATION. Capitalized terms
used, but not defined, herein shall have the meanings given to such terms in the
Purchase Agreement referred to below.

            WHEREAS, each Originator and the Seller entered into that certain
Receivables Sale Agreement, dated as of March 19, 2002 (as amended to the date
hereof, the "Original Sale Agreement", and as amended hereby, the "Sale
Agreement");

            WHEREAS, the Seller, Blue Ridge, each other Lender, the Servicer and
the Agent entered into that certain Receivables Purchase Agreement, dated as of
March 19, 2002 (as amended to the date hereof, the "Original Purchase
Agreement", as amended hereby, the "Purchase Agreement", the Original Purchase
Agreement, together with the Original Sale Agreement are referred to herein as
the "Original Agreements" and the Purchase Agreement and the Sale Agreement are
referred to herein as the "Agreements"); and

            WHEREAS, the parties hereto desire to amend each of the Original
Agreements;

            NOW THEREFORE, in consideration of the premises and the other mutual
covenants contained herein, the parties hereto agree as follows:

      SECTION 1. Sale of Sulfuric Acids Business.

      (a) Arch hereby represents and warrants as follows:

            (i) Arch plans to sell, prior to September 30, 2003, its sulfuric
acids business in North America, consisting of (i) the marketing, sale and
provision of sulfuric acid regeneration services, (ii) the manufacturing,
marketing, sale and distribution of virgin sulfuric acid, (iii) the marketing,
sale and provision of disposal services for waste fuels, and (iv) the
manufacturing, marketing, sale and distribution of sodium bisulfite solution,
but excluding the manufacturing, marketing, sale or distribution of any acid (or
substitute product) to the semiconductor or other electronic components
industries (collectively, the "Sulfuric Acids Business");

<PAGE>

            (ii) Arch and the Seller intend to sell all outstanding Receivables
and Related Security relating to the Sulfuric Acids Business, all of which are
currently, and as of the Sale Date (as defined below) will be, owned by the
Seller (the "Sulfuric Acids Business Receivables");

            (iii) Arch will not be able to notify, prior to the Sale Date,
Obligors of the Sulfuric Acids Business Receivables of the sale of the Sulfuric
Acids Business and/or cause such Obligors, prior to the Sale Date, to make
payments of such Receivables to a P.O. Box other than a Lock-Box or have
collections of such Receivables deposited to a bank account other than a
Collection Account; and

            (iv) for a period of no more than one hundred twenty (120) days
after the Sale Date (such period being the "Interim Period"), collections
relating to the Sulfuric Acids Business Receivables may be sent to a Lock-Box
and/or deposited in a Collection Account.

      (b) Arch hereby requests that:

            (i) on the Sale Date, the Seller be permitted to sell the Sulfuric
Acids Business Receivables to Arch on the date hereof for a repurchase price to
be determined by Arch and the Seller, subject to approval by the Agent (the
"Repurchase Price");

            (ii) on the Sale Date, the Agent, Blue Ridge and the Seller each
release their interests in the Sulfuric Acids Business Receivables, including
liens thereon;

            (iii) for the Interim Period, the Agent permit the collections of
the Sulfuric Acids Business Receivables to be made to the Lock-Boxes and the
Collection Accounts; and

            (iv) the Servicer be permitted, on the terms and conditions set
forth herein, to remove from the Collection Accounts upon identification by the
Servicer thereof all Collections received in respect of the Sulfuric Acids
Business Receivables.

      SECTION 2. Amendments to Agreements and Waivers Relating to the Sale of
Sulfuric Acids Business.

      The parties hereto agree that the Agreements shall be amended, modified
and supplemented by the following amendments, agreements and waivers,
notwithstanding any provision of any of the Agreements to the contrary:

      (a) Arch agrees that at least two (2) Business Days prior to the day on
which it closes the sale of the Sulfuric Acids Business (the "Sale Date") it
will provide written notice thereof to the Seller and the Agent, which notice
shall set forth the Sale Date, the proposed Repurchase Price and the aggregate
Outstanding Balance of the Sulfuric Acids Business Receivables as of the date of
such notice.

      (b) On the Sale Date (i) each of the Seller Parties shall be deemed to
reaffirm all representations and warranties made by it in Article V of the
Purchase Agreement and to agree that all such covenants, representations and
warranties shall be deemed to have been remade as of the Sale Date, (ii) each of
the Seller Parties shall be deemed to represent and warrant that no

                                        2

<PAGE>

Amortization Event or Unmatured Amortization Event has occurred and be
continuing as of the Sale Date, (iii) each of the Originators shall be deemed to
reaffirm all representations and warranties made by it in Article II of the Sale
Agreement and to agree that all such covenants, representations and warranties
shall be deemed to have been remade as of the Sale Date and (iv) each of the
Originators shall be deemed to represent and warrant that no Termination Event
or Unmatured Termination Event shall have occurred and be continuing as of the
Sale Date.

      (c) On the Sale Date, unless the Agent shall have notified Arch not later
than 2:00 p.m. (New York City time) on the Business Day immediately preceding
the Sale Date, that the Agent disagrees with the Repurchase Price, the Seller
shall, without further action, irrevocably sell, transfer and assign to Arch,
upon receipt by the Seller of the Repurchase Price in accordance with the terms
hereof, without recourse, representation or warranty, all right, title and
interest of the Seller in, to and under all of the Sulfuric Acids Business
Receivables outstanding on the Sale Date, together with all Related Security
related thereto.

      (d) On the Sale Date, Arch shall pay the Repurchase Price to the Agent's
Account by wire transfer in immediately available funds and the Agent shall
apply such amount to the reduction of the Aggregate Invested Amount, accrued
Yield on such amount of the Aggregate Invested Amount so repaid and accrued Fees
on such amount of the Aggregate Invested Amount so repaid.

      (e) Upon receipt by the Agent of the Repurchase Price in the Agent's
Account in the manner provided for herein, the Agent, the Seller and Blue Ridge
and their respective successors and assigns shall, without further action,
irrevocably release in full each of their respective interests in all of the
Sulfuric Acids Business Receivables and all Related Security related thereto,
including but not limited to any security interests therein. The Agent and Blue
Ridge each agree to take such further actions, at Arch's sole cost and expense,
that Arch may reasonably request to evidence or confirm such releases.

      (f) Arch, in its capacity as Servicer, shall (i) as soon as reasonably
practicable after the Sale Date (but in no event later than the second Business
Day after the Sale Date), provide written notice to the Seller and the Agent of
the final aggregate Outstanding Balance of all Sulfuric Acids Receivables sold
on the Sale Date (the "Sale Date Sulfuric Acids Receivables Balance") and (ii)
from and after the Sale Date, identify within two (2) Business Days after
receipt, all collections received in any Collection Account constituting
collections received in respect of the Sulfuric Acids Business Receivables.

      (g) Immediately upon identification of any Collections received in respect
of the Sulfuric Acids Business Receivables, Arch, as Servicer, shall remove such
collections received in respect of the Sulfuric Acids Business Receivables from
the related Collection Account, up to an aggregate amount at any time not to
exceed the Sale Date Sulfuric Acids Receivables Balance.

      (h) Arch, as Servicer, agrees that it will provide to the Agent on the
first Business Day of each week for each week following the Sale Date through
and including the earlier of (i) the week in which the last Sulfuric Acids
Business Receivable is paid in full and (ii) the week in which the 120th day
after the Sale Date occurs, additional written reporting satisfactory to the

                                        3

<PAGE>

Agent relating to the Collections received in respect of the Sulfuric Acids
Business Receivables during the preceding week.

      (i) Arch agrees that, if the Sulfuric Acids Business Receivables have not
been paid in full by the 120th day after the Sale Date, it will send notices to
each obligor of any unpaid Sulfuric Acids Business Receivable instructing such
obligor to make all payments on such Sulfuric Acids Business Receivables to such
other lock-box or post office box that is not owned by the Seller as Arch may
choose.

      (j) Arch and the Seller each hereby agrees to indemnify (and pay upon
demand to) each Indemnified Party (as defined in the Purchase Agreement) and its
assigns, officers, directors, agents and employees from and against any and all
damages, losses, claims, taxes, liabilities, costs, expenses and for ail other
amounts payable, including reasonable attorneys' fees and disbursements awarded
against or incurred by any such Indemnified Party arising out of or related to
any Sulfuric Acids Business Receivables and any Collection relating to any
Sulfuric Acids Business Receivables.

      (k) Subject to the satisfaction of the above terms and conditions and
provided that no Amortization Event or Unmatured Amortization Event has
occurred, the Seller, Blue Ridge and Wachovia, upon receipt of the Repurchase
Price as provided above, shall, without further action, be deemed to waive any
default under the Transaction Documents that may result from the receipt of any
collections received in respect of the Sulfuric Acids Business Receivables in
any Collection Account during the Interim Period; provided, however, this waiver
shall not, except as expressly provided herein, operate as a waiver of any
right, power or remedy of the Agent, any Lender or any other Secured Party under
any of the Transaction Documents.

      SECTION 3. Agreements in Full Force and Effect as Amended.

      (a) Except as specifically amended hereby, each of the Original Agreements
shall remain in full force and effect. This Amendment shall not constitute a
novation of any or all of the Original Agreements, but shall constitute an
amendment of each such Original Agreement only. The parties hereto agree to be
bound by the terms and conditions of each Original Agreement, as amended by this
Amendment, as though such terms and conditions were set forth herein.

      (b) As of the date first set forth above, each reference in the Original
Agreements to "this Agreement", "hereunder", "hereof", "herein" or words of like
import shall mean and be, and any references to such Agreement in any other
document, instrument or agreement executed and/or delivered in connection with
the Original Purchase Agreement shall mean and be, a reference to such Original
Agreement as amended hereby.

      (c) The Seller hereby agrees that in addition to any costs otherwise
required to be paid pursuant to the Transaction Documents, the Seller shall pay
the reasonable legal fees and out-of-pocket expenses of the Agent's counsel,
Hunton & Williams, and all audit fees and due diligence costs incurred by the
Agent in connection with the consummation of this Amendment and the transactions
contemplated by this Amendment, including, without limitation, in connection
with the Sale Date and the Interim Period.

                                        4

<PAGE>

      SECTION 4. Conditions to Effectiveness of this Amendment.

The amendments set forth herein shall not be effective until the date on which
the Agent shall have received authorized signatures from each of the
Originators, the Servicer and the Seller.

      SECTION 5. Miscellaneous.

      (a) This Amendment may be executed in any number of counterparts, and by
the different parties hereto on the same or separate counterparts, each of which
shall be deemed to be an original instrument but all of which together shall
constitute one and the same agreement. Delivery of an executed counterpart of a
signature page to this Amendment by facsimile shall be as effective as delivery
of a manually executed counterpart of a signature page to this Amendment.

      (b) The descriptive headings of the various sections of this Amendment are
inserted for convenience of reference only and shall not be deemed to affect the
meaning or construction of any of the provisions hereof.

      (c) This Amendment may not be amended or otherwise modified except as
provided in the Agreement.

      (d) THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES UNDER
THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED AND ENFORCED IN ACCORDANCE
WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REFERENCE TO ITS CONFLICT OF LAWS
PROVISIONS (INCLUDING SECTION 5-1401 OF THE GENERAL OBLIGATIONS LAW BUT
OTHERWISE WITHOUT REGARD TO CONFLICTS OF LAW PRINCIPLES).

                   [Remainder of Page Intentionally Left Bank]

                                        5

<PAGE>

      IN WITNESS WHEREOF, the parties have caused this Agreement to be executed
by their respective officers thereunto duly authorized, as of the date first
above written.

                                        ARCH CHEMICALS RECEIVABLES CORP.,
                                        as the Seller

                                        By:  /s/ W. Paul Bush
                                             -----------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH CHEMICALS, INC.,
                                        as an Originator and as the Servicer

                                        By: /s/ W. Paul Bush
                                            ------------------------------
                                          Name: W. Paul Bush
                                          Title: VP & Treasurer

                                        ARCH SPECIALTY CHEMICALS, INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                            ------------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH CHEMICALS SPECIALTY PRODUCTS, INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                            ------------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH ELECTRONIC CHEMICALS, INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                            ------------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

<PAGE>

                                        ARCH WOOD PROTECTION INC.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                            ------------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

                                        ARCH PERSONAL CARE PRODUCTS, L.P.,
                                        as an Originator

                                        By: /s/ W. Paul Bush
                                            ------------------------------
                                          Name: W. Paul Bush
                                          Title: Treasurer

<PAGE>

                                        BLUE RIDGE ASSET FUNDING CORPORATION

                                        BY: Wachovia Securities, LLC
                                        as Attorney-in-Fact

                                        By: /s/ Douglas R. Wilson, Sr.
                                            ------------------------------
                                        Title: Vice President

                                        WACHOVIA BANK, NATIONAL ASSOCIATION
                                        as a Liquidity Bank and as Agent

                                        By: /s/ Gary G. Fleming, Jr.
                                           ------------------------------
                                        Title: Director

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