<PAGE>
                                                                   Exhibit 10.36

                                                                  EXECUTION COPY

                                SEVENTH AMENDMENT
                                 WITH RESPECT TO
                             NOTE PURCHASE AGREEMENT

         THIS SEVENTH AMENDMENT WITH RESPECT TO NOTE PURCHASE AGREEMENT is
entered into as of July 17, 2001 among HERCULES INCORPORATED, a Delaware
corporation (the "Company"), which is successor to BetzDearborn Inc.
("BetzDearborn") under the Note Agreement referred to below, PUTNAM FIDUCIARY
TRUST COMPANY ("Putnam"), in its capacity as successor Trustee (the "Trustee")
of The BetzDearborn Inc. Employee Stock Ownership and 401(k) Trust (the "ESOT")
of the BetzDearborn Inc. Employee Stock Ownership and 401(k) Plan (the "Plan"),
the undersigned subsidiaries of the Company and THE PRUDENTIAL INSURANCE COMPANY
OF AMERICA ("Prudential").

                              W I T N E S S E T H:

         WHEREAS, BetzDearborn adopted the Betz Laboratories, Inc. Employee
Stock Ownership Plan (the "Plan") effective January 1,1989, changed the name of
the Plan to the name shown above and most recently amended and restated the Plan
effective January 1,1994; and

         WHEREAS, pursuant to the Plan and effective January 1,1989,
BetzDearborn entered into an Agreement of Trust with Mellon Bank, N.A.
("Mellon") as trustee ("Trustee"), thereby establishing the ESOT; and

         WHEREAS, as of June 19,1989, the ESOT and BetzDearborn entered into a
Note Purchase Agreement with Prudential whereby the ESOT sold and Prudential
purchased $100,000,000 principal amount of the ESOT's Notes (guaranteed by
BetzDearborn), approximately $75,461,000 of which are still outstanding and held
by Prudential, which Purchase Agreement was amended by a First Amendment thereto
as of June 25,1996 and a Second Amendment thereto as of June 25,1998 and which
was supplemented and amended by a Consent and Waiver and Assumption (the
"Consent and Assumption") effective October 15, 1998 executed by and among
BetzDearborn, the Company and Prudential and further amended by a Third
Amendment and Assumption Agreement (the "Third Amendment") dated as of December
31,1998 executed by and among BetzDearborn the Company and Prudential, a Fourth
Amendment dated as of April 19,1999 among the parties hereto, a Fifth Amendment
dated as of July 26, 2000 among the parties thereto and a Sixth Amendment dated
as of November 14, 2000 among the parties hereto (as so amended and supplemented
by said Amendment and the Consent and Assumption being herein called the "Note
Agreement"); and

         WHEREAS, as of October 1, 1992, BetzDearborn removed Mellon as Trustee,
appointed Putnam as successor Trustee and amended and restated the foregoing
Agreement of Trust, retitling it as "Trust Agreement for Betz Laboratories Inc.
Employee Stock Ownership and 401 (k) Plan," and continued the ESOT with the
successor Trustee; and
<PAGE>
         WHEREAS, pursuant to an Agreement and Plan of Merger dated as of July
30, 1998 among the Company, Water Acquisition Co. and BetzDearborn, BetzDearborn
became a wholly-owned subsidiary of the Company on October 15, 1998 (the
"Merger"); and


         WHEREAS, pursuant to the Consent and Amendment and the Third Amendment
(i) the Company has assumed all of the obligations of BetzDearborn under the
Note Agreement and in respect of the ESOT Notes and BetzDearborn has been
released from all such obligations (except insofar as BetzDearborn shall have
obligations as a Guarantor under the Note Agreement), and (ii) the Company has
succeeded to, and been substituted for, and is entitled to exercise every right
and power of, "the Company" under the Note Agreement; and


         WHEREAS, the parties hereto desire to amend certain provisions of the
Note Agreement, as provided for herein.

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

SECTION 1. AMENDMENTS TO NOTE AGREEMENT


         (a) Subparagraph 5.2(a)(i) of the Note Agreement is hereby amended and
restated in its entirety to read as follows:


                  (i) Leverage Ratio. It will not permit, as of the last day of
         any fiscal quarter, the Leverage Ratio to exceed the ratio set forth
         below for the applicable period:


<TABLE>
<CAPTION>
               Period                                   Maximum Leverage Ratio
               ------                                   ----------------------
<S>                                                     <C>
October 1, 2000 through June 30, 2001                         4.75 to 1.0
July 1, 2001 through September 30, 2001                       5.25 to 1.0
October 1, 2001 through December 31, 2001                     5.00 to 1.0
January 1, 2002 through March 31, 2002                        4.75 to 1.0
April 1, 2002 through June 30, 2002                           4.50 to 1.0
July 1, 2002 and thereafter                                   4.25 to 1.0
</TABLE>



         (b) Subparagraph 5.2(a)(iii) of the Note Agreement is hereby amended
and restated in its entirety to read as follows:


                  (ii) Interest Coverage Ratio. It will not permit as of the
         last day of any fiscal quarter, the Interest Coverage Ratio to be less
         than the ratio set forth below for the applicable period:


<TABLE>
<CAPTION>
               Period                            Maximum Interest Coverage Ratio
               ------                            -------------------------------
<S>                                              <C>
October 1, 2000 through June 30, 2001                      1.75 to 1.0
July 1, 2001 through September 30, 2001                    1.65 to 1.0
October 1, 2001 through December 31, 2001                  1.75 to 1.0
January 1, 2002 and thereafter                             2.00 to 1.0
</TABLE>



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<PAGE>
         (c) The definition of "Asset Disposition" in Paragraph 12A of the Note
Agreement is hereby deleted in its entirety and the following substituted
therefor;


                  "Asset Disposition": the disposition of any or all of the
         assets (including without limitation the Capital Stock of a Subsidiary)
         of the Company or any of its Subsidiaries whether by sale, lease,
         transfer or otherwise (including a disposition pursuant to any casualty
         or condemnation event, but excluding a disposition pursuant to a
         Permitted Receivables Financing). The term "Asset Disposition" shall
         not include (i) the sale of inventory in the ordinary course of
         business, (ii) the sale or disposition of machinery and equipment no
         longer used of useful in the conduct of such Person's business, (iii)
         any Equity Issuance by the Company, (iv) intercompany transfers from a
         Credit Party of a wholly-owned Subsidiary of a Credit Party to a Credit
         Party, (v) intercompany transfers from any wholly-owned Subsidiary of a
         Credit Party (which Subsidiary is not itself a Credit Party or a First
         Tier Foreign Subsidiary) to any wholly-owned Subsidiary of a Credit
         Party or (vi) intercompany transfers from a First Tier Foreign
         Subsidiary to another First Tier Foreign Subsidiary as long as the
         Company can demonstrate pursuant to documentation reasonably
         satisfactory to the Collateral Agent that the Collateral Agent's
         security interest in the Pledged Shares (as defined in the Pledge
         Agreements) of such First Tier Foreign Subsidiary receiving the assets
         is as perfected as the Collateral Agent's security interest in the
         prior First Tier Foreign Subsidiary.


         (d) The definition of "Consolidated EBITDA" in Paragraph 12A of the
Note Agreement is hereby deleted in its entirety and the following substituted
therefor:


                  "Consolidated EBITDA": for any fiscal period, (i) Consolidated
         Net Income for such period, plus (ii) Consolidated Interest Expense for
         such period, plus (iii) to the extent deducted in computing such
         Consolidated Net Income, the sum of (a) taxes, (b) depreciation, (c)
         amortization, (d) any non-cash charges, (e) for the fiscal quarter
         ended June 30, 2001 through the fiscal quarter ended lime 30, 2002
         only, any non-recurring cash charges associated with the restructuring
         of the Company end its Subsidiaries initiated on or after April 1, 2001
         in an aggregate amount not to exceed $50 million and (f) any
         extraordinary, unusual or non-recurring cash losses or cash charges
         incurred in connection with (x) the Acquisition in an amount not to
         exceed $170 million after taxes in the aggregate for all such add-backs
         pursuant to this sublease (x) and (y) the settlement prior to the
         Closing Date of certain litigation in an amount not to exceed $63
         million after taxes in the aggregate for all such add-backs pursuant to
         this subclause (y), minus (iv) any extraordinary gains and noncash
         gains.


         (e) The definition of "Consolidated Net Worth" in Paragraph 12A of the
Note Agreement is hereby deleted in its entirety and the following substituted
therefor:


                  "Consolidated Net Worth": as of the end of the most recently
         ended calendar month, the sum of (i) all items that would be included
         under stockholders' equity on a consolidated balance sheet of the
         Company and its



                                       3
<PAGE>
         Consolidated Subsidiaries plus, (ii) insurance reserves. Consolidated
         Net Worth shall be determined in accordance with generally accepted
         accounting principles substantially the same as those used by the
         Company in preparing the financial statements referred to in
         subparagraph 3.2 of the Third Amendment and on a consolidated basis
         substantially the same as that used by the Company in preparing such
         financial statements; provided however, that neither (A) foreign
         currency translation adjustments under Financial Accounting Standards
         Board Statement No. 52, "Foreign Currency Translation", (B) items
         reported in comprehensive income and accumulated other comprehensive
         income under Financial Accounting Standards Statement No. 130
         (including but not limited to gains or losses for derivatives
         designated as a hedge of exposure to variable cash flows of forecasted
         transactions and derivatives designated as a hedge of foreign currency
         exposure of a net investment in a foreign operation) nor (C) items and
         charges related to the impairment of goodwill in connection with the
         Acquisition to the extent, in the amount and only for so long as
         required by generally accepted accounting principals, shall in any case
         be taken into account in calculating Consolidated Net Worth.

SECTION 2. ACKNOWLEDGMENT AND AFFIRMATION BY CREDIT PARTIES

         Each Credit Patty affirms the liens and security interests created and
granted by it in the Credit Documents (including, but not limited to, the Pledge
Agreement, the Security Agreement and the Mortgages) and agrees that this
Amendment shall in no manner adversely affect or impair such liens and security
interests.

SECTION 3. REPRESENTATIONS AND WARRANTIES OF CREDIT PARTIES


         In order to induce Prudential to enter into this Amendment, each of the
Credit Parties makes the following representations, covenants and warranties
which shall survive the execution and delivery of the Credit Documents:


                  (i) It has taken necessary action to authorize the execution,
         delivery and performance of this Amendment.


                  (ii) This Amendment has been duly executed and delivered by
         such Credit Party and constitutes such Credit Party's legal, valid and
         binding obligation, enforceable in accordance with its terms, except as
         such enforceability may be limited (x) by general principles of equity
         and conflicts of laws of (y) by bankruptcy, reorganization, insolvency,
         moratorium or other laws of general application relating to or
         affecting the enforcement, of creditors' rights.



                  (iii) No consent, approval, authorization or order of, or
         filing, registration or qualification with, any court or governmental
         authority or third party is required in connection with the execution,
         delivery or performance by such Credit Party of this Amendment.


                  (iv) The execution and delivery of this Amendment does not
         diminish or reduce its obligations under the Credit Documents
         (including, without limitation, in the


                                       4
<PAGE>
         case of each Guarantor, such Guarantor's guaranty pursuant to paragraph
         6 of the Note Agreement) in any manner, except as specifically set
         forth herein.

                  (v) Such Credit Party has no claims, counterclaims, offsets,
         or defenses to the Credit Documents and the performance of its
         obligations thereunder, or if such Credit Party has any such claims,
         counterclaims, offsets, or defenses to the Credit Documents or any
         transaction related to the Credit Documents, the same are hereby
         waived, relinquished and released in consideration of Prudential's
         execution and delivery of this Amendment.


                  (vi) The representation and warranties of the Credit Parties
         set forth in Section 3 of the Third Amendment are true and correct as
         of the date hereof (except those that relate to an earlier date) and
         all of the provisions of the Credit Documents, except as amended
         hereby, are in full force and effect.


                  (vii) Subsequent to the execution and delivery of this
         Amendment and after giving effect hereto, no unwaived event has
         occurred and is continuing which constitutes a Default or an Event of
         Default.


         The Credit Parties hereby incorporate the representations and
warranties contained in Section 1 of the Credit Agreement (together with all
related defined terms) as in effect on the date hereof (and after giving effect
to the Fourth Amendment to Amended and Restated Revolving Credit Agreement,
executed on or about the date hereof by the Company, certain subsidiaries of the
Company, BetzDearborn Canada, Inc., Bank of America, N.A., Bank of America
Canada, and the several banks and financial institutions identified on the
signature pages thereto) by reference herein to the same extent as if set forth
at length herein (the "Incorporated Provisions") and each hereby makes such
representations and warranties (to the knowledge of the Company, when applicable
under the Credit Agreement) for the benefit of Prudential as of the date hereof
in connection with the execution and delivery of this Amendment; provided, that
references in the Incorporated Provisions to "this Agreement" and "Notes" shall
be taken as references to the Note Agreement as amended hereby and to the Notes
outstanding thereunder. The Company represents and warrants to Prudential that
no Default or Event of Default exists under the Note Agreement, both before and
after giving effect to the provisions of this Amendment.


SECTION 4. EFFECTIVENESS OF AMENDMENTS

         The provisions of this Amendment shall become effective upon the
execution and delivery of a counterpart of this Amendment by all of the parties
hereto and the satisfaction of the following additional conditions precedent:


         (a) Prudential shall have received counterparts of this Amendment, of
the Fourth Amendment With Respect to Note Purchase Agreement, dated as of April
19, 1999, and of the Waiver, dated as of April 5, 2001, among the parties
hereto, duty executed and delivered by each of the Credit Parties and by the
Trustee;


         (b) no Default or Event of Default shall have occurred and be
continuing;


                                       5
<PAGE>
         (c) Prudential shall have received an amendment fee in an amount equal
to $75,461;

         (d) Prudential shall have received from a Responsible Officer of the
Company a certificate to the effect that as of the date of the effectiveness of
this Amendment all representations and warranties made by the Company and each
other Credit Party in this Amendment and each other Credit Document are true and
correct in all material respects.

SECTION 5. MISCELLANEOUS

         Section 5.1. Defined Terms. Capitalized terms not otherwise defined
herein shall have the meanings ascribed thereto in the Note Agreement.


         Section 5.2. References. On and after the effective date of this
Amendment, each reference in the Note Agreement and the Notes shall mean and be
a reference to the Note Agreement as amended by this Amendment.



         Section 5.3. Expenses. The Company agrees to pay all reasonable costs
and expenses incurred by Prudential in connection with the preparation,
execution and delivery of this Amendment, and the consummation of the
transactions contemplated hereby, including the reasonable fees and expenses of
Prudential's counsel.


         Section 5.4. Ratification The Note Agreement, as amended by this
Amendment, is and shall continue to be in full force and effect and is hereby in
all respects modified and confirmed. Except as expressly modified and amended in
this Amendment, all of the terms, provisions end conditions of the Credit
Documents shall remain unchanged and in full force and effect.


         Section 3.5. Counterparts. This Amendment may be executed in any number
of counterparts and by any combination of the parties hereto is separate
counterparts, each of which counter shall be an original and all of which taken
together shall constitute one and the same agreement.



         Section 5.6. Governing Law. THIS AGREEMENT AND THE RIGHTS AND
OBLIGATIONS OF THE PARTIES UNDER THIS AGREEMENT SHALL BE GOVERNED BY, AND
CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK.



                                       6
<PAGE>
         IN WITNESS WHEREOF, the parties have caused this Amendment to be
executed and delivered by their respective officers thereunto duly authorized as
of the date first above written.

ESOT:

                                               BETZDEARBORN INC. EMPLOYEE STOCK
                                               OWNERSHIP AND 401(K) TRUST
                                               ESTABLISHED BY THE BETZDEARBORN
                                               INC. EMPLOYEE STOCK OWNERSHIP AND
                                               401(K) PLAN


                                               By:      PUTNAM FIDUCIARY TRUST
                                                        COMPANY as Trustee

                                               By:
                                                  ------------------------------
                                               Name:
                                                    ----------------------------
                                               Title:
                                                     ---------------------------


PRUDENTIAL:                                    THE PRUDENTIAL INSURANCE COMPANY
                                               OF AMERICA

                                               By:
                                                  ------------------------------
                                               Name:
                                                    ----------------------------
                                               Title:
                                                     ---------------------------


COMPANY:                                       HERCULES INCORPORATED, A DELAWARE
                                               CORPORATION

                                               By:
                                                  ------------------------------
                                               Name:
                                                    ----------------------------
                                               Title:
                                                     ---------------------------



                                       7
<PAGE>
SUBSIDIARY GUARANTORS
(list continues on the next page):

                                        BETZDEARBORN CANADA, INC.
                                          an Ontario corporation
                                        HERCULES CREDIT, INC.
                                          an Delaware corporation
                                        HERCULES FLAVOR, INC.,
                                          a Delaware corporation
                                        WSP, INC.
                                          a Delaware corporation
                                        AQUALON COMPANY,
                                          a Delaware corporation
                                        HERCULES FINANCE COMPANY,
                                          a Delaware partnership

                                        FIBERVISIONS, L.L.C.,
                                          a Delaware limited liability company

                                        FIBERVISIONS INCORPORATED,
                                          a Delaware corporation
                                        FIBERVISIONS PRODUCTS, INC.,
                                          a Georgia corporation
                                        BETZDEARBORN, INC.,
                                          a Pennsylvania corporation
                                        BETZDEARBORN EUROPE, INC.,
                                          a Delaware corporation
                                        DRC, LTD.,
                                          a Delaware corporation

                                        BL TECHNOLOGIES, INC.,
                                          a Delaware corporation

                                        BLI HOLDINGS CORP.
                                          a Delaware corporation
                                        HERCULES SHARED SERVICES
                                        CORPORATION, a Delaware corporation
                                        BETZDEARBORN INTERNATIONAL,
                                        INC., a Pennsylvania corporation

                                        (execution on behalf of the foregoing
                                        Subsidiary Guarantors is on the
                                        following page)


                                       8
<PAGE>
SUBSIDIARY GUARANTORS

(continued from previous page):


                                        ATHENS HOLDINGS, INC.,
                                          a Delaware corporation
                                        BETZDEARBORN CHINA, LTD.,
                                          a Delaware corporation
                                        BL CHEMICALS INC.,
                                          a Delaware corporation
                                        CHEMICAL TECHNOLOGIES INDIA, LTD.,
                                          a Delaware corporation
                                        COVINGTON HOLDINGS, INC.,
                                          a Delaware corporation
                                        EAST BAY REALTY SERVICES, INC.,
                                          a Delaware corporation
                                        FIBERVISIONS, L.P.,
                                          a Delaware partnership
                                        HERCULES CHEMICAL CORPORATION,
                                          a Delaware corporation
                                        HERCULES COUNTRY CLUB, INC.,
                                          a Delaware corporation
                                        HERCULES EURO HOLDINGS, LLC,
                                          a Delaware limited liability company

                                        HERCULES INTERNATIONAL LIMITED, L.L.C.,
                                          a Delaware limited liability company

                                        HERCULES INVESTMENTS, LLC,
                                          a Delaware Limited liability company
                                        HISPAN CORPORATION,
                                        a Delaware corporation

                                        By:
                                           -------------------------------------
                                        Name:
                                             -----------------------------------
                                        Title:
                                              ----------------------------------

                                        for each of the foregoing Subsidiary
                                        Guarantors listed on this page and the
                                        preceding page



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